1. health and fitness
2. disease
3. cholesterol

CHARACTERIZATION OF PECTIC SUBSTANCES
EXTRACTED FROM ORANGE (Citrus sinensis) PEELS
By
Wisal El Musafa Elsiddig Mohamed
B.Sc. (Agric) Honours
University of Khartoum
1995
A dissertation Submitted In Partial Fulfillment of the Requirements
for the Degree of Master of Science in Food Science and Technology
Supervisor
Dr. Babiker Elwasila Mohamed
Department of Food Science and Technology
Faculty of Agriculture
University of Khartoum
June - 2005
DEDICATION
To the soul of my Father,
To my dear family..
Mother, brothers and
sisters
To my dear friends
and colleagues
With love and respect
j|átÄ
Acknowledgement
I would like to express my gratitude and thanks to my
supervisor Dr. Babiker El Wasila Mohamed for his helpful and
constructive supervision which was vital to the success of the
research.
My thanks and recognition are extended to Ustz. Huda Abdalla
Mohamed, Food Industries Department, Industrial Research and
Consultancy Centre. My thanks and appreciation are extended to
every body who helped me during this study.
Above all, my thanks and praise to Allah who gave me
patience and will to accomplish this work.
ABSTRACT
Pectic substance of two types of orange peels (yellow and
green) were investigated. Samples were obtained from the local
market. The orange fruits were washed, peeled and then the peels
dried and ground.
The study involved chemical composition, alcohol insoluble
solids of orange peels and isolation of orange peels pectic substances,
which were assayed and characterized for their moisture, ash,
alkalinity, protein, acetyl content, methoxyl content, total carboxyl
groups, anhydrogalacturonic acid, equivalent weight, calcium,
magnesium, degree of esterification, intrinsic viscosity and molecular
weight.
Results showed that yellow and green orange peels contained
6.72% and 7.92% moisture, 2.90% and1.85% ash, 5.84%and 6.65%
protein, 8.30% and 9.47% fibre, 3.08% and 2.75% oil, 0.43% and
0.40% titrable acidity, 60.09mg/100gm and 34.95mg/100gm ascorbic
acid, 11.01% and 5.03% reducing sugar, 16.62% and 7.77% total
sugars, 0.78mg/100g and 0.83mg/100gm calcium, 0.19mg/100g and
0.18mg/100gm magnesium and 50.55% and 60.74% alcohol insoluble
solids respectively.
The results showed that alcohol insoluble solids of the two
types contained 2.92% and 5.63% moisture, 4.09% and 4.48% ash,
7.65% and 7.49% protein, 14.84% and 16.06% pectin, 0.22mg/100gm
and 0.21mg/100gm calcium and 0.12mg/100gm and 0.11mg/100mg
magnesium respectively.
The results obtained, indicated that green orange peels contain
relatively higher percentage of pectin compared to yellow orange
peels. Total pectin was found to be 14.48% for yellow type and
16.06% for green type. The methoxyl content was 8.95% and 8.87%
respectively. The acetyl content was found to be 0.44%, for yellow
peels and 0.46% for green type. The degree of esterification was
estimated to be 73.8% for yellow type and 72.47% for green type. The
total carboxyl groups were found to be 1.96meq/gm for yellow type
and 1.98meq/gm for green type. The anhydrogalacturonic acid content
was 68.99% and 69.49%, respectively. The equivalent weight was
estimated to be 974.60 and 920.73 respectively. The viscosity was
2.2/g/dl and 2.07g/dl respectively. The molecular weight was
estimated to be 4.2 × 104 for yellow type and 4.03 × 104 for green
type. The ash content was 3.14% and 3.37% respectively. The protein
content was 3.57% and 3.44% respectively. The calcium content was
found to be 0.28mg/100gm for yellow type and 0.3mg/100gm for
green type. The magnesium content was estimated to be
0.09mg/100gm and 0.07mg/100gm, respectively.
The results, obtained in this study, indicated that both quantity
and quality of pectin obtained from orange peels (yellow and green)
are suitable for the commercial production of pectins.
‫ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ‬
‫ﺧﻼﺻﺔ اﻷﻃﺮوﺣﺔ‬
‫ﺃﺠﺭﻴﺕ ﺍﻟﺩﺭﺍﺴﺔ ﻋﻠﻰ ﻨﻭﻋﻴﻥ ﻤﻥ ﻗﺸﻭﺭ ﺍﻟﺒﺭﺘﻘﺎل ﻫﻤﺎ‪ :‬ﺍﻷﺼـﻔﺭ ﻭﺍﻷﺨـﻀﺭ ﻭﻗـﺩ‬
‫ﺃﺴﺘﺠﻠﺒﺕ ﺍﻟﻌﻴﻨﺎﺕ ﻤﻥ ﺍﻟﺴﻭﻕ ﺍﻟﻤﺤﻠﻲ ﻟﺘﻘﻴﻴﻡ ﺍﻟﻤﻭﺍﺩ ﺍﻟﺒﻜﺘﻴﻨﻴﺔ‪ .‬ﻏﺴﻠﺕ ﺜﻤﺎﺭ ﺍﻟﺒﺭﺘﻘﺎل ﻭﺠﻔﻔـﺕ‬
‫ﺍﻟﻘﺸﺭﺓ ﺜﻡ ﺴﺤﻨﺕ‪.‬‬
‫ﺸﻤﻠﺕ ﺍﻟﺩﺭﺍﺴﺔ ﺘﺤﺩﻴﺩ ﺍﻟﻤﻜﻭﻨﺎﺕ ﺍﻟﻜﻴﻤﻴﺎﺌﻴﺔ ﻭﺍﻟﻤﻜﻭﻨﺎﺕ ﻏﻴﺭ ﺍﻟﺫﺍﺌﺒـﺔ ﻓـﻲ ﺍﻟﻜﺤـﻭل‬
‫ﻟﻘﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل ﻭﺇﺴﺘﺨﻼﺹ ﺍﻟﻤﻭﺍﺩ ﺍﻟﺒﻜﺘﻴﻨﻴﺔ ﻤﻥ ﻗﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل ﻟﻤﻌﺭﻓﺔ ﺨﺼﺎﺌﺼﻬﺎ ﺍﻟﻜﻴﻤﻴﺎﺌﻴﺔ‬
‫ﻤﻥ ﺤﻴﺙ ﺍﻟﻤﺤﺘﻭﻱ ﺍﻟﻤﻴﺜﻭﻜﺴﻴﻠﻲ‪ ،‬ﺍﻟﻤﺤﺘﻭﻯ ﺍﻷﺴﺘﻴﻠﻲ‪ ،‬ﺩﺭﺠﺔ ﺍﻷﺴـﺘﺭﺓ‪ ،‬ﻤﺤﺘـﻭﻯ ﺤﻤـﺽ‬
‫ﺍﻷﻨﻬﻴﺩﺭﻭﻴﻭﺭﻭﻨﻙ‪ ،‬ﺍﻟﻌﺩﺩ ﺍﻟﻜﻠﻲ ﻟﻤﺠﻤﻭﻋﺔ ﺍﻟﻜﺎﺭﺒﻭﻜﺴﻴل‪ ،‬ﺍﻟﻭﺯﻥ ﺍﻟﻤﻜﺎﻓﺊ‪ ،‬ﺍﻟﻠﺯﻭﺠﺔ‪ ،‬ﺍﻟـﻭﺯﻥ‬
‫ﺍﻟﺠﺯﻴﺌﻲ‪ ،‬ﺍﻟﻜﺎﻟﺴﻴﻭﻡ‪ ،‬ﺍﻟﻤﺎﻏﻨﺯﻴﻭﻡ‪ ،‬ﻨﺴﺒﺔ ﺍﻟﺭﻤﺎﺩ ﻭﻨﺴﺒﺔ ﺍﻟﺒﺭﻭﺘﻴﻥ‪.‬‬
‫ﺃﻅﻬﺭﺕ ﺍﻟﺩﺭﺍﺴﺔ ﺃﻥ ﺍﻟﻨﻭﻋﻴﻥ )ﺍﻷﺼﻔﺭ ﻭﺍﻷﺨﻀﺭ( ﻤﻥ ﻗﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل ﻴﺤﺘﻭﻱ ﻋﻠﻰ‬
‫‪ %6.72‬ﻭ‪ %7.92‬ﺭﻁﻭﺒﺔ‪ %2.9 ،‬ﻭ‪ %1.85‬ﺭﻤﺎﺩ‪ %5.84 ،‬ﻭ‪ %6.65‬ﺒﺭﻭﺘﻴﻥ‪%8.30 ،‬‬
‫ﻭ‪ %9.47‬ﺃﻟﻴــﺎﻑ‪ %3.08 ،‬ﻭ‪ %2.75‬ﺯﻴــﺕ‪ %0.43 ،‬ﻭ‪%0.4‬ﺍﻟﺤﻤﻭﻀــﺔ‪60.09 ،‬‬
‫ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻭ ‪ 34.95‬ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻓﻴﺘﺎﻤﻴﻥ‪ %11.01 ،C‬ﻭ ‪ %5.03‬ﺴﻜﺭﻴﺎﺕ ﻤﺨﺘﺯﻟﺔ‪،‬‬
‫‪ %16.62‬ﻭ‪ %7.77‬ﺴﻜﺭﻴﺎﺕ‪ 0.78 ،‬ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻭ‪ 0.83‬ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻜﺎﻟﺴﻴﻭﻡ‪0.19 ،‬‬
‫ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻭ‪ 0.18‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ ﻤﺎﻏﻨﺯﻴﻭﻡ ﻭ‪ %50.55‬ﻭ ‪ %60.74‬ﻤﻭﺍﺩ ﻏﻴﺭ ﺫﺍﺌﺒـﺔ‬
‫ﻓﻲ ﺍﻟﻜﺤﻭل ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ‪.‬‬
‫ﻜﻤﺎ ﺃﻭﻀﺤﺕ ﺍﻟﻨﺘﺎﺌﺞ ﺃﻥ ﺍﻟﺠﺯﺀ ﻏﻴﺭ ﺍﻟـﺫﺍﺌﺏ ﻓـﻲ ﺍﻟﻜﺤـﻭل ﻟﻠﻨـﻭﻋﻴﻥ ﺍﻷﺼـﻔﺭ‬
‫ﻭﺍﻷﺨﻀﺭ ﻴﺤﺘﻭﻯ ﻋﻠﻰ ‪ %2.92‬ﻭ‪ %5.63‬ﺭﻁﻭﺒﺔ‪ %4.09 ،‬ﻭ‪ %4.48‬ﺭﻤـﺎﺩ‪%7.55 ،‬‬
‫ﻭ‪ %7.49‬ﺒــﺭﻭﺘﻴﻥ‪ %14.48 ،‬ﻭ‪ %16.06‬ﺒﻜﺘــﻴﻥ‪ 0.22 ،‬ﻤﻠﺠــﻡ‪100/‬ﺠــﻡ‪0.21 ،‬‬
‫ﻤﻠﺠﻡ‪100/‬ﺠﻡ ﻜﺎﻟﺴﻴﻭﻡ ﻭ‪ 0.12‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ ﻭ‪ 0.11‬ﻤﻠﺠﻡ‪ 100/‬ﺠـﻡ ﻤـﺎﻏﻨﺯﻴﻭﻡ ﻋﻠـﻰ‬
‫ﺍﻟﺘﻭﺍﻟﻲ‪.‬‬
‫ﻜﻤﺎ ﺩﻟﺕ ﺍﻟﻨﺘﺎﺌﺞ ﺃﻥ ﻗﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل ﺍﻷﺨﻀﺭ ﺘﺤﺘﻭﻯ ﻋﻠﻰ ﻨﺴﺒﺔ ﺃﻋﻠﻰ ﻤﻥ ﺍﻟﺒﻜﺘـﻴﻥ‬
‫ﻤﻘﺎﺭﻨﺔ ﺒﻘﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل ﺍﻷﺼﻔﺭ‪ .‬ﻭﻟﻘﺩ ﻭﺠﺩ ﺃﻥ ﻤﺤﺘﻭﻯ ﺍﻟﺒﺭﺘﻘـﺎل ﺍﻷﺼـﻔﺭ ﻤـﻥ ﺍﻟﺒﻜﺘـﻴﻥ‬
‫‪ %14.48‬ﺒﻴﻨﻤﺎ ﺍﻟﺒﺭﺘﻘﺎل ﺍﻷﺨﻀﺭ ‪) %16.06‬ﻋﻠﻰ ﺃﺴﺎﺱ ﺍﻟﻭﺯﻥ ﺍﻟﺠﺎﻑ(‪ .‬ﺃﻤـﺎ ﺍﻟﻤﺤﺘـﻭﻯ‬
‫ﺍﻟﻤﻴﺜﻭﻜﺴﻴﻠﻲ ‪ %8.95‬ﻭ‪ 8.87‬ﻟﻠﺒﻜﺘﻴﻥ ﻤﻥ ﺍﻟﻌﻴﻨﺘﻴﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ ﻭﻟﻘﺩ ﻭﺠـﺩ ﺃﻥ ﺍﻟﻤﺤﺘـﻭﻱ‬
‫ﺍﻷﺴﺘﻴﻠﻲ ‪ %0.44‬ﻟﻠﻨﻭﻉ ﺍﻷﺼﻔﺭ ﻭ‪ %0.46‬ﻟﻠﻨﻭﻉ ﺍﻷﺨـﻀﺭ‪ .‬ﻗـﺩﺭﺕ ﺩﺭﺠـﺔ ﺍﻷﺴـﺘﺭﺓ‬
‫ﺒـ‪ %73.8‬ﻭ‪ %72.47‬ﻟﻠﻌﻴﻨﺘﻴﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ‪ .‬ﺍﻟﻌﺩﺩ ﺍﻟﻜﻠﻲ ﻟﻤﺠﻤﻭﻋﺔ ﺍﻟﻜﺎﺭﺒﻭﻜـﺴﻴل ﻓﻬـﻭ‬
‫‪ 1.96‬ﻤﻠﻡ ﻤﻜﺎﻓﻲ ﻟﻜل ﺠﺭﺍﻡ ﻟﻠﻨﻭﻉ ﺍﻷﺼﻔﺭ ﻭ ‪ 1.98‬ﻤﻠﻡ ﻤﻜﺎﻓﻲ ﻟﻜل ﺠﺭﺍﻡ ﻟﻠﻨﻭﻉ ﺍﻷﺨـﻀﺭ‬
‫ﻭﻭﺠﺩ ﺃﻥ ﻤﺤﺘﻭﻯ ﺤﻤﺽ ﺍﻷﻨﻬﻴﺩﺭﻭﻴﻭﺭﻭﻨﻙ ‪ %68.99‬ﻭ ‪ %69.49‬ﻟﻠﻨﻭﻋﻴﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ‪.‬‬
‫ﻗﺩﺭ ﺍﻟﻭﺯﻥ ﺍﻟﻤﻜﺎﻓﺊ ﺒـ ‪ 974.60‬ﻟﻠﻨﻭﻉ ﺍﻷﺼﻔﺭ ﻭ‪ 920.73‬ﻟﻠﻨﻭﻉ ﺍﻷﺨﻀﺭ‪ ،‬ﺃﻤﺎ ﺍﻟﻠﺯﻭﺠـﺔ‬
‫ﻓﻬﻲ ‪ 2.21‬ﺠﻡ‪/‬ﺩﻴﺴﻠﺘﺭ ﻭ‪2.09‬ﺠﻡ‪/‬ﺩﻴﺴﻠﺘﺭ ﻟﻠﻌﻴﻨﺘﻴﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ ﻭﻗﺩﺭ ﺍﻟﻭﺯﻥ ﺍﻟﺠﺯﺌـﻲ ﺒــ‬
‫‪ 4.2 x 104‬ﻟﻠﻨﻭﻉ ﺍﻷﺼﻔﺭ ﻭ ‪ 4.03 x 104‬ﻟﻠﻨﻭﻉ ﺍﻷﺨﻀﺭ‪ .‬ﻜﺎﻨﺕ ﻨـﺴﺒﺔ ﺍﻟﺭﻤـﺎﺩ ﺘﻌـﺎﺩل‬
‫‪ %3.14‬ﻭ ‪ 3.37‬ﻟﻠﻨﻭﻋﻴﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ ﻭﻨﺴﺒﺔ ﺍﻟﺒﺭﻭﺘﻴﻥ ‪ %3.57‬ﻭ‪ %3.44‬ﻋﻠﻰ ﺍﻟﺘـﻭﺍﻟﻲ‪.‬‬
‫ﻜﻤﺎ ﻭﺠﺩ ﺃﻥ ﻤﺴﺘﻭﻯ ﺍﻟﻜﺎﻟﺴﻴﻭﻡ ‪ 0.28‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ ﻟﻠﻨﻭﻉ ﺍﻷﺼﻔﺭ ﻭ‪ 0.30‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ‬
‫ﻟﻠﻨﻭﻉ ﺍﻷﺨﻀﺭ ﻭﻗﺩﺭ ﻤﺤﺘﻭﻯ ﺍﻟﻤﺎﻏﻨﺯﻴﻭﻡ ﺒـ ‪ 0.09‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ ﻭ ‪ 0.07‬ﻤﻠﺠﻡ‪ 100/‬ﺠﻡ‬
‫ﻟﻠﻨﻭﻋﻴﻥ ﺍﻷﺼﻔﺭ ﻭﺍﻷﺨﻀﺭ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ‪ .‬ﻴﺘﻀﺢ ﻤﻥ ﺘﻠﻙ ﺍﻟﻨﺘـﺎﺌﺞ ﺍﻟﻤﺘﺤـﺼل ﻋﻠﻴﻬـﺎ ﺃﻥ‬
‫ﺍﻟﺒﻜﺘﻴﻥ ﺍﻟﻤﺴﺘﺨﻠﺹ ﻤﻥ ﻗﺸﺭﺓ ﺍﻟﺒﺭﺘﻘﺎل )ﺍﻷﺼﻔﺭ ﻭﺍﻷﺨﻀﺭ( ﻤﻨﺎﺴﺏ ﻹﻨﺘﺎﺝ ﺍﻟﺒﻜﺘﻴﻥ ﺍﻟﺘﺠﺎﺭﻱ‬
‫ﻤﻥ ﺤﻴﺙ ﺍﻟﻜﻤﻴﺔ ﻭﺍﻟﻨﻭﻋﻴﺔ‪.‬‬
LIST OF CONTENTS
Page
Dedication…………………………………………………………………………………..
i
Acknowledgement ………………………….……………………………………………
ii
Abstract ………………………………………………………………………………………
iii
Arabic Abstract …………………………...………………………………………………
iv
List of Contents ………………………..…………………………………………………
v
List of Tables………………………………….……………………………………………
ix
CHAPTER ONE: INTRODUCTION………...………………………………
1
CHAPTER TWO: LITERATURE
REVIEW…….………………………
4
2.1 History of citrus culture………..…………………………………………………
4
2.2. Origin and history of orange………..…………………………………………
5
3.2 Characteristics of some orange varieties………..…………………………
7
2.4 Uses of orange fruit………..……………………….………………………………
8
2.5 Chemical composition of orange peel………..……………………………
10
2.6. Pectic substance………..……………………………………………………………
12
2.6.1 Structure and composition of pectic substances……………………
15
2.6.2. Properties of pectic substances………..……..……………………………
16
2.6.3. Extraction of pectic substance………..……………………………………
19
2.6.4. Uses of pectin………..……………………………………..……………………
21
2.6.5. Sources of the pectin substances………..…………………………………
23
2.6.6. Properties of orange peel pectin………..…………………………………
24
CHAPTER THREE: MATERIALS AND METHODS……..………
26
3.1. Materials………..…………………………….………………………………………
26
3.1.1. Chemicals………………………………..…………………………………………
26
3.1.2. Raw material…………………………....…………………………………………
26
3.2. Analysis of orange peels………….…..…………………………………………
26
3.2.1. Proximate analysis………..………………….…………………………………
26
3.2.2. Alcohol insoluble solids (AIS) ………..…………………………….……
26
3.2.3. Titrable acidity………..…………………….……………………………………
27
3.2.4. Ascorbic acid content…….….……..…………………………………………
28
3.2.5. Sugars………..………………………………………………………………………
29
3.2.5.1. Reducing sugars…………………….…………………………………………
29
3.2.5.2. Total sugar………..…………………………..…………………………………
29
3.2.6. Calcium and magnesium…………...…………………………………………
30
3.3. Preparation and analysis of alcohol insoluble solids………..………
31
3.3.1. Preparation of alcohol insoluble solids (AIS) ………..……………
31
3.3.2. Analysis of alcohol insoluble solids………..…………………………
31
3.3.2.1. Proximate analysis………..…………………………………………………
31
3.4. Isolation of orange peels pectins………..……………………………………
32
3.5. Quantitative analysis of the isolated pectin………...……………………
33
3.5.1. Moisture………..….…………………………..……………………………………
33
3.5.2.Ash………..……………………………………………………………………………
33
3.5.3. Ash alkalinity……………………….…..…………………………………………
34
3.5.4. Equivalent weight……………...……..…………………………………………
34
3.5.5. Methoxyl content………..………………………………………………………
35
3.5.6. Acetyl content………..………………………..…………………………………
36
3.5.7. Anhydrouronic acid (AUA) content………..……………………………
37
3.5.8. Viscosity………..…………….………………………..……………………………
37
3.6. Statistical analysis……………………….…………………………………………
39
CHAPTER FOUR: RESULTS AND DISCUSSIONS ………………
40
4.1 Chemical composition of orange peels………..………………..…………
40
4.2. Analysis of alcohol insoluble solids (AIS) ………..……………………
45
4.3. Properties of orange peels pectin substances……………………………
48
4.4. Conclusions and recommendations…………………………………………
58
4.4.1. Conclusions………..………….……………………………………………………
57
4.4.2 Recommendations……………………..…………………………………………
58
REFERENCES………………………...…………………………………………………
59
LIST OF TABLES
Table Title
1.
Analysis of orange peels grams/100 grams (on dry weight
basis) …………...……………………………….………………………………
2.
3.
No.
41
Analysis of alcohol insoluble solids (AIS) grams/100
grams (on dry weight basis) …………….…............……….…………
46
Properties of orange peels pectic substances……….……..……
51
LIST OF FIGURES
Fig.
Title
1.
The effect of party number and lactation stage on moisture
content of camel milk………………………………………………………
2.
45
The effect of party number and season on total solids content
of camel milk…………………………………………………………………
9.
44
The effect of lactation stage and season on moisture content
of camel milk……………………………………………………………
8.
36
The effect of party number and season on moisture content of
camel milk…………………………………..…………………………………
7.
33
The effect of party number and lactation stage on moisture
content of camel milk………………………………………………………
6.
31
The effect of party number and lactation stage on lactose
content of camel milk………………………………………………………
5.
28
The effect of party number and lactation stage on ash content
of camel milk…………………………………………………………………
4.
26
The effect of party number and lactation stage on total solid
content of camel milk………………………………………………………
3.
No.
47
The effect of lactation stage and season on total solid content
of camel milk…………………………………………………………………
48
CHAPTER ONE
INTRODUCTION
The sweet orange (Citrus sinensis) constitutes one of the world’s
most popular and recognizable fruit crops .Sweet oranges are regarded
as high source of ascorbic acid and other fruit acids. Physically, citrus
fruits consist of 40-50% juice, 20-40%rind and 20-35% pulp and
seeds. Chemically, they contain 86-92%water, 5-8% sugar and 1-2%
pectin lesser amounts of acids, protein, essential oils and
minerals(janick et al., 1981).
The global market for juice and juice product was estimated to be
about 50 billion liters in the late 1990 in the United State of America
alone, the retail commercial value of the 20 billion liters of juice and
juice products exceeded 18billion US$ (Bates et al.,2001). In
production of juices and concentrates large amounts of solid wastes
accumulate consisting of peels, pulp, seeds, stem, skin, cores and pits
(Tressler and joslyn, 1961). In fruit processing industry seeds and
peels are discarded as waste at present. The problems arising from
disposal of waste stress the needs of research
to
develop
an
acceptable commodity from waste (Srirangarajan and Shrikhande,
1979). However, researchers have explored possibilities of using these
components in other ways (Braddock and Crandall, 1981) for
examples, the pigmented part of peel has been suggested as a potential
source of natural carotenoids (Wilson et al., 1971; Braddock and
Kesterson, 1974).
Over 400 by-products can be made from citrus in addition to
juice (Bates et al.,2001). The utilization of solid wastes either directly
as cattle feed or after drying or fermentation and either utilization for
production of various by-products is more economical (Tressler and
joslyn, 1961).
Pectin has been manufactured from citrus peel for more than 50
years. All citrus contain pectin and richest sources are lime, lemons,
oranges (Bates et al., 2001) and grapefruit (Mohamed, 1999). Tropical
developing countries may have a locally owned pectin in
manufacturing operation, but it is typically hard pressed to compete
imported pectin unless the native operation is given governmental
protection. Typically pectin are co-located with large-scale juice
operations that run at least30000 metric ton (MT) per year of fruit. A
handful of manufacturers make the majority of pectin. Curiously, all
of pectin used in the United States of America is imported, principally
from Europe, central and south America (Bates et al., 2001).
In the Sudan, citrus peels are normally thrown as waste during
processing of citrus products since no pectin industry exist in the
Sudan the utilization of citrus peels as a source of pectin might be
economically sound and reduces its importation (Mohamed, 1999).
Previous work indicated that appreciable amounts of pectin can
be obtained from grapefruit peels (Mohamed, 1999) and therefore the
objective of this work is to extend the knowledge in this area of
research. This can be achieved through extraction and characterization
of pectic substances from orange peels.
CHAPTER TWO
LITERATURE REVIEW
2.1 History of citrus culture
Citrus is the largest fruit crop in the world with about
60.000.000 metric ton (MT) grown (Bates et al., 2001). Citrus is
grown in two belts on both sides of Equator from about 20-40 degrees
of latitude (Soost and Roose, 1996; Bates et al., 2001). The place of
origin of nearly all species of citrus fruits was probably the southern
Himalaya mountain. Columbus brought citrus seeds to the western
hemisphere in 1493 and planted
them
first
on the island of
Hispaniola, now called Haiti (Bates et al., 2001).
Citrus became commercialized in Americans in the late 1800s.
In the early to mid 1900s the principal producing states were Florida,
Texas and California in United States(Bates et al., 2001). The total
area covered by citrus plantation is 2.9 million hectares. Fifty percent
of citrus growing occurs in northern and central America and
Mediterranean region. South America, the far east and southern
hemisphere, including South Africa and Australia are responsible for
25%, 50% and 5%, respectively (Soost and Roose, 1996). Citrus is
botanically a large family whose dominant members are the sweet
orange (Citrus sinensis), mandarin or tangerine orange (Citrus
reticulata), grapefruit (Citrus paradisi), lemon (Citrus limon) and lime
(Citrus aurantifolia)(Bates et al., 2001).
In the Sudan, the first records of citrus introduction are of the
Merowe garden in the old Dongla province as reported by Mohamed
(1999). Citrus production in the Sudan is mainly located along the
narrow strips of the alluvial soils of the main River Nile, Blue Nile,
White Nile, Gezira province, Kordofan, Gebal Marra and the Southern
region. Citrus crop at present constitute a good source of cash for
farmer, especially in the areas where relatively high population
intensities exist,
e.g. the central region and Khartoum province.
Consequently, both private and public sectors were stimulated to
expand citrus production (El-Hassan, 1989).
2.2. Origin and history of orange:
The location of the origin of the sweet orange is controversial
china, India, Bhutan, Burma and Malaysia are among the countries of
origin. The path of sweet orange culture may have first flowed from
Yunnan to upper Burma (Speigel- Roy and Goldschmidt, 1996). In the
sixth and seventh centuries, Muslim armies overran a vast territory
stretching from India to Spain, orange and other citrus trees decorate
trail. Arab traders introduced further varieties of citrus fruit to Europe
in the middle ages. The Portuguese introduced variety of sweet orange
from India which quickly replaced a bitter form (Mcphee, 1967).
The numerous health benifits of citrus become apparent to
Europeans during the age of exploration. Portuguese, Spanish, Arab
and Dutch sailors planted citrus trees along trade routes to prevent
scurvy (Mcphee, 1967; Soost and Roose, 1996; Solley, 1997). As an
order each sailor on a Spanish headed for the Americans had to
carry100seeds with him (Mcphee, 1967).
Orange and tangerines account for approximately 70% of global
citrus production (Janick et al., 1981). Orange production far outstrips
the production of all others citrus. Brazil leads the world’s orange
production with 19 million MT in 1996 to 1997 (Bates et al., 2001).
The orange plantings in the Sudan are primarily centred in
narrow strips of silt soils along the River Nile and its tributaries, the
Blue and white Niles and in Kassala area where the soils are deep and
fertile. The orange yield and quality in these soils are very
satisfactory. However, the small arable land hindered further
expansion of orange in these traditional orange production areas. At
present policy for the agricultural development in the Sudan, calls for
an active role of horticultural production in the national economy. The
policy has encouraged many citrus growers to look for high yielding
varieties that are adapted to the irrigated heavy clay soils of central
Sudan, which form the vast cultivable land of the country, to meet the
present and future expansion of orange plantings. To achieve these
goals, intensive research programmes on different citrus species have
been initiated in the central region of Sudan with its huge resources of
water and arable land (Hamid et al., 1999).
3.2 Characteristics of some orange varieties:
It has long known that there are three main groups of orange,
the sweet orange, the mandarin and sour orange. The most important
physical characteristic of orange to be considered are size, color,
shape, rind, seeds, flesh and falvour (Kotschevar, 1961).
The physical properties of Valencia orange were reported by
Kotschevar (1961). Valencia orange was reported to have a large size
and a pale to yellow orange colour with tendency to show green. The
shape is slightly oval and the rinds are smooth. The number of seeds
per fruit was found to be between 2 to 5 and the flavour was excellent.
The quality of citrus involves good tastes, good appearance,
high nutritive value and sufficient stamina to reach the consumer in
attractive condition. The factors governing these are width, rind
thickness, number of seeds, juice volume, acidity, total soluble solid
(TTS) and ascorbic acid content (Hamid et al., 1999). The properties
of specific cultivars of orange (Hamlin, Butter, Complall, Olinda,
Jaffa, Diller, Forst and Sinnari) were reported by Hamid et al. (1999).
The range of rind thickness was found between 4.1 and 6.5mm. One
of the main quality attributes in citrus fruit is amount of juice and its
composition. The volume of juice per fruit ranged from 64.4 to
78.4ml, where as the juice percentage by weight varied from 29-40%,
with Olinda and Sinnari leading and Jaffa Trailing in both aspects.
The taste of citrus correlates well with (TSS): Acid ratio. Forst had
highest ascorbic acid content.
The quantitative amount changed according to the fruit variety,
fertilizer applied, irrigation practices and region of growth (Nour et
al., 1981). The California Valencia orange juice contained the amino
acids alanine, asparagine, arginine, proline, serine and possibly lysine
and glutamine (Nour et al., 1981).
2.4 Uses of orange fruit:
Oranges are primarily eaten fresh or prepared as frozen juice
concentrate (Janick et al., 1981). The basic type of orange juice are
chilled orange juice, frozen concentrate orange juice and hot back
juice (Bates et al., 2001). Other products of orange are canned orange
juice for infants, powder orange juice (Tressler and Joslyn, 1961), Jam
and marmalade (EL-Mubarak et al, 1977; Fellows, 1997).
Orange juice powder is sold for use in food manufacturing,
adding flavour, colour and nutritive elements to bakery goods. Orange
slices and orange peel are candied as confection. Granted peel is much
use as flavouring and essential oil is employed commercially as food,
soft-drink and candy flvaour and for other purpose (Morton, 1987).
Citrus peel and other juice extractor residues have traditionally
been dried and marketed as cattle feed (Kesterson and Braddock,
1976; Janick et al., 1981) and molasses as well as flavouring
perfumes, pharmaceuticals and soap. The extract of rinds and seeds
include pectin and oil. When fermented, orange juice produce vinegar
(Janick et al., 1981). originally, citrus uses include beautification,
embalming, protection from poisons and
curing fever and colic
(Solley ,1997). Before Europeans viewed oranges as food, the people
use their trees, flowers and fruits as ornaments, seasoning and for
aromas (Mcphfee, 1967).
Orange peel albedo is a good source of dietary fiber (Branddock
and Crandall, 1981). Orange waste can be utilized for production of
fungal protein (Labeneiab et al., 1979) and could be used as source of
pectic substance (EL_Mubarak et al., 1977).
2.5 Chemical composition of orange peel:
The peel, which consist of an outer flavedo and inter albedo, serves to
protect edible portion or inner pulp of the fruit. Two flavedo
component which may indirectly affect the quality of juice are
chromaplasts and oil vesicles. The chromaplasts contain carotenoids
.Beneath the flavedo is white spongy layer called albedo. Within this
layer a number of important constituent namely flavanones, limonin,
pectin and fiber are present( Nelson and Tressler, 1980). The
composition of citrus fruit is affected by such factors as growing
conditions various treatments and practices, maturity, root stock and
variety (Tressler and Joslyn,1961).
The moisture content of fruit and vegetables varies from 6696% and its variable even in some variety depending upon locality
and other environmental factors. Protein contents depend on variety,
agricultural practices and availability of nitrogen in soil (Mohamed,
1999). Protein content of dry citrus peel is reported to be 6%
(Braddock and Crandall, 1981).
The free sugars in citrus peel are predominantly sucrose,
glucose and fructose although the xylose is present in trace amounts
(Ting and Attaway, 1971). The amounts of soluble carbohydrates of
peel and pulp of citrus fruit are correlated with stage of fruit maturity
(Mohamed, 1999). As the alcohol-soluble fraction of the peel increase,
there is a corresponding decrease of the alcohol-insoluble solids which
are mainly the cell wall and cytoplasmic constituents. Ting and
Attaway (1971) reported 6.81% total sugar content of sweet orange
peel and pith.
The proportion of some constituents of citrus are greatly
influenced by maturity e.g. the amount of water-soluble sugar and
water-soluble pectin increase with increasing maturity. Carbohydrate
separate into alcohol-soluble solids and alcohol insoluble solid. The
alcohol soluble solids (ASS) consisted largely of sugars, mainly
reducing sugars, together with small amount of low polymer
galacturonides and such substance as essential oils, waxes, organic
acids and flavonids. The alcohol insoluble solids (AIS) comprise the
cell wall component, principally pectic substance, hemicelluloses and
cellulose (Kefford, 1959).
Essential oils are contained in specialized gland, imbedded
mainly in the outer rind but also in extremely small amounts in juice
vesicles. The fat content of orange peel is 2.25% (Monselise, 1980).
The main acids of the citrus peel are oxalic, malic, malonic with
some citric (Ting and Attaway, 1971).The concentration of ascorbic
acid in citrus fruit is affected by a number of factors such growing
conditions, root stock, position of fruit on the tree and maturity,
(Tressler and Joslyn, 1961). Ascorbic acid is present in relatively high
amount in mature citrus fruit. Concentrations are much higher in rind
(Monselise, 1980).
2.6. Pectic substance:
According to Pilink and Voragen (1970) the American chemical
society has given the following definition:Pectic substance is a group designation for those complex,
colloidal carbohydrate derivatives which occur in, or are prepared
from plants and contain large proportion of anhydrogalacturonic acid
unit which are thought to exist in chain-like combination. The
carboxyl groups of polygalacturonic acid may be partly esterified by
methyl groups and partly or completely neutralized by one or more
bases.
The terms used in the field of pectin research are very general.
Protopectin is applied to the water insoluble parent pectic substance
which occurs in plants and which upon restricted hydrolysis yields
pectin or pectinic acid.
The term pectinic acid is used for colloidal poly galacturonic
acids containing more than a negligible proportion of methyl ester
groups. Pectinic acids under suitable condition are capable of forming
gels with sugar and acid or, if suitably low in methoxyl content, with
certain metalic ions.
The general term pectin designates those water-soluble pectin of
varying methyl ester content and degree of neutralization which are
capable of forming gels with sugar and acid under suitable conditions.
Pectic acids are pectic substance mostly composed of colloidal poly
galacturonic acid and essentially free from methyl ester groups. The
salts of pectic acid are either normal or acid pectates.
Physiological life of fruit processing and storage of fruit
products are accompainied by changes in pectin content and pectin
structure. These may involve degree of esterification, molecular
weight, neutral sugar component and acetylation. These changes may
be enzymic or chemical in nature (Pilink and Voragen, 1970).
Changes in pectic polymers have been described in many
process such as canning, lactic fermentation and heat treatment, but
very little is known about change due to alkaline treatment as shown
by Jimenez et al., (1996). From the literature reviewed by
Abdelrahman (2002), it can be concluded that during storage of sugar
beet, water soluble pectin increased and total pectin decreased and this
can
be
attributed
mainly
to
enzymic
degradation,
namely
polygalacturonase and pectin methyl esterase. Cooking helps
increasing the solubility of pectic substance.
Pectic polysaccharides are important determinants of fruit
texture (Jimenez et al., 1996). Pectins degradation during processing
ultimately affects the tissue texture i.e. the firmness of tissue may be
off set to a certain degree. The firmness in clingstone peaches is
related to retention of protopectin (Mohamed, 1999).
The texture change during ripening of fruits involves the cell
wall degradation, which consists of a dissolution of the pectin-rich
middle lamella region. At biochemical level, the important
modification that can be observed during ripening are loss of neutral
sugar,
an
increase
in
pectin
solubility
and
progressive
depolymerization of the pectins (Batisse et al., 1996). Pectic enzymes
contribute to development of desirable texture produced during
ripening of plant (Owen, 1985).
Mangoes undergo a very rapid softening of the mesocarp as
they approach full ripeness. This dramatic softening is presumably due
to the release of depolymerizing enzymes which rapidly attack the
constituents of cell walls in the mesocarp, including the pectic
substances (Nour, 1978). Several studies revealed that the major
cleavage reaction leading to vegetable softening was B-eliminative
depolymerization of intercellular pectins (Smits et al., 1995).
Many fruits and vegetables transformation processes, involve
treatments with calcium to preserve their firmness (Labelle, 1971;
Howard and Buescher, 1990). Calcium in plants is normally found in
the cell wall forming calcium bridges between the residues of
galacturonic acid belong to adjacent pectic chains. The calcium-pectin
complex formed acts as an intercellular cement to give firmness to
vegetable tissues. The presence of calcium, in addition to favouring
insuitability
of
pectic
material,
inhibits
its
degradation
by
polygalacturonase (Burns and Pressy, 1987). During the normal fruit
maturation process the calcium cations are Tranlocated to the growing
zones in the plant (Marchiner, 1986). This has been linked to the
solubilization and degradation of the pectic material of the middle
lamella, causing the softening of the fruits (Lidster et al., 1978; Filslycaon and Buret, 1990).
2.6.1 Structure and composition of pectic substances:
Pectic substance are heteropolysaccharide. They consist of
galacturonan, araban and galactan of which the central component was
galacturonan. The main galacturonan is composed of α-D-(1-4)
galacturonic acid with varying a mount of methyl ester groups on the
carboxyl groups. Some of carboxyl groups are free acid and some are
neutralized with various ions (MCcready, 1970). Many pectins have
neutral sugars covalently linked to them as a side chains (Pilnik and
Voragen, 1970) including arabinose, galactose, rhamnose, xylose and
other sugar (McCready, 1970).
Earlier work reviewed by Mohamed (1999) confirmed the
presence of the neutral polymers. A mixture of pectic substance
including pectic acid was extracted using ammonium oxalate and
partial acid hydrolysis of pectic acid furnished L-rhamnose, Larabinose, D-galactose, D-galactouronic acids, 2 methyl-L-xylose and
some other monomers. Further evidence for L-arabinose as
constitutent sugar in pectic substances was confirm by Foglitti and
Percheron (1968) from carnation roots and Aspinall et al., (1968) from
lemon peel.
Sugars separated by partial acid hydrolysis of pectic fractions of
grapefruit peel are arabinose, galactose, rhamnose and xylose together
with galacturonic acid (Mohamed, 1999). The neutral Sugar isolated
from pumpkin pectin are arabinose, galactose and rhamnose together
with galacturonic acid (Eltinay et al, 1982).
The non galacturonic, materials constitute one-third of pectic
materials weight. The characteristic properties of pectin gelation, film
formation and high viscosity in dilute solution are derived from the
polygalacturonide chain and non-galacturonide materials act as
diluent . These non-galacturonide materials are covalently bound as
branch chain expect rhamnose which is believed to be interrupting the
main polygalacturonic chain as weak interceptions (Mohamed, 1999).
2.6.2. Properties of pectic substances:
Pectic substances have many unique physical and chemical properties
primarily owening to carboxyl group (McCready, 1970). They posses
many colloidal characteristics (Mohamed, 1999). The pectic solutions
of lime, orange and grape peels were characterized by determination
of their equivalent weight, acetyl content, methoxyl content,
anhydrouronic acid, moisture, ash content and calcium (El-Mubarak et
al., 1977). In addition El-tinay et al. (1982) studied ash alkalinity,
protein, degree of estrification and total carboxyl group in pumpkin
pectic substances.
Pectins are soluble in water and form viscous solution. The
viscosity depending on molecular weight and being influenced by
degree of esterification, pH and electrolyte concentration (MC cready,
1970). Positive correlation between the viscosity and pectin has been
evidenced by Nso et al. (1998). The relative viscosity of pectin
solution varies with concentration in a manner similar to that other
ionizable hydrophilic colloids and certain salts (Abdel-rahman, 2002).
The intrinsic viscosity of some fruit and vegetable pectin ranged from
0.75 dl/g to 5.9 dl/g (Fishman, 1991). Pectin extracted from mango
fruits. Nour (1977) showed very low intrinsic viscosity compared with
commercial citrus pectin.The
intrinsic viscosity in mango pectin
ranged from 0.86 dl/g to 1.43 dl/g (Abdelrahman, 2002) and guava
pectin from 0.2 dl/g to 0.5 dl/g (Eltinay et al, 1979).
Acetyl content comprises an integral constituent of peel pectin
although it is not an essential constituent of pectin in general. Pectin
from fruit differ from that sugar beet in being practically devoid of
acetyl group (Abdelrahman, 2002). The acetyl content of citrus pectin
is 0.32% (lime), 0.46% (orange), 0.314% (sweet orange). Alexandar
and Sulebele (1980), 0.455 – 1.634% (grapefruit)(Mohamed, 1999)
and 0.215 – 0.314% in mango pulp pectin (Abdelrahman, 2002).
One aspect of difference among the pectic substances in their
degree of esterification (DE) which decrease somewhat as plant
ripening takes place. The DE is defined as the number of esterified Dgalacturonic acid residues per total number of D- galacturonic
residues x 100 (Owens, 1985). The DE of some fruits is reported
guava pectin is 69.3 – 80.6% (ELtinay et al., 1979) and that of citrus
pectin is 67% (Nour, 1977) while mango pulp pectin is reported to be
87.0% (Abdelrahman, 2002). Pectin with DE above 70% tends to
form a jelly more rapidly or at higher temperature than one with 50–
70%, pectin with low degree of esterification i.e. less than 50% are not
commonly used to make high solid gels, because they tend to
precipitate so rapidly and form irregular gels (Abdel-rahman, 2002).
All pectic substances contain methoxyl groups in varying
amount depending upon the source and method of preparation
(Abdelrahman, 2002). The methoxyl content of guava pectin is found
to be 3.32% (Eltinay et al., 1979).
The ash content of pumpkin pectin is reported to represent 3.42
– 4.84% (Eltinay et al., 1982). The anhydrouronic acid content of
pumpkin pectin ranged between 71.6% and 76.8% (Eltinay et al.,
1982) and guava pectin between 23.1 and 26.4% (Eltinay et al., 1979).
The most important property of pectin and indeed the
characteristic property is the ability to form gels. High methoxyl
pectin in aqueous solution form gels in presence of secondary gelling
agents of non- Electrolyte character, such as sucrose, solutions of
some cations such as calcium to form gels of different character in the
absence of secondary gelling agents. The quality of pectin as a gel
forming agent is a function of methxyl content and distribution of
methoxyl groups,anhydrouronic acid, molecular weight and size of
polymer, content, nature and distribution of non-uronide residues and
the acetyl content (Nour, 1978).
2.6.3. Extraction of pectic substance:
It was well known that pectic substances exist in fruits and
vegetables as protopectin. The highest concentration of protopectin is
found in growing tissues. This is changed to soluble pectinic acids
during growth or ripening of plant tissue due to the slow action of
plant acids or more rapid action of the pectic enzymes. The efficiency
of extraction methods is related to time, temperature and pH at time of
extraction (Baker, 1948).
Hot alcohol extraction of plant material separates the
carbohydrates into soluble and insoluble fractions. The soluble
fraction is made of mono- and disaccharides together with starch and
dextrin and other low molecular weight compounds. The alcohol
insoluble fraction includes the higher molecular weight compounds,
these are cell wall compounds together with protein and some
inorganic matter (Sinclair and Crandall, 1953). The high temperature
would inactivate the enzyme especially pectinases. In most plant
tissues, pectic substances are present insoluble forms (Aspinall et al.,
1968) .The latter required acids or agents for its extraction. Grinding
the tissue with 0.05N HCl at 80ºc for 30 minutes results in exhausting
the tissue and probably complete extraction of pectic material. Acid
extraction is preferred because it lowers the amount of hemicellulose
in the extract (Whistler and Smart, 1953). However, The acid will
bring about continuous degradation and hydrolysis of pectic
substances and hence keeping the extraction time to a minimum is
recommended (Mohamed, 1999).
Total extraction of pectic substances is also accomplished by
certain salts, such as ammonium oxalate, that dissolve the calcium
pectate through double decomposition. The alkaline extraction of
pectic substances is rarely used. complete extraction of pectic
substance was achieved by the use of sodium hexametaphosphate
solution which can form a calcium complex (Boothby, 1980).
The extraction of pectiv is followed by purification through
filtration or by the addition of appropriate enzymes system (Whistler
and Smart, 1953). Many organic solvents can be used for precipitation
such as alcohol and acetone which produce a firmer and easily
handled product. The alcohol precipitate usually contains 20– 50% of
non uronide matter as ash, nitrogenous constituents, hemicelluloses
and glucosans. As pectin is a mixture of uronide and non uronide
substances, greater variations are expected in its properties
(Mohamed, 1999).
2.6.4. Uses of pectin:
Pectin is a component of nearly all fruits and vegetables and can
be extracted and used in food processing to form characteristic gels in
jam, marmalade (Fellows, 1997) and jellies (Bates et al., 2001) as well
as for the confectionary industry (Pilink and Voragen, 1970). The use
of pectin in jams and jellies preserves has two major purposes:
creation of desired texture and binding of water. If the water binding
effect is not achieved completely, the final gel will show a tendency to
contract and exude juice, known as syneresis (Bates et al., 2001).
Besides the jelly formation property of pectin it helps in reducing the
boiling time, which in turn assists in preserving the volatile substances
and prevent the excessive inversion of sugar (Saeed and Elmubarak,
1974).
There are two types of pectin: high methoxyl (HM) pectins that
form gels in high solids jam (above 55% solids) in a pH range of 2.0 –
3.5 and low methoxyl (LM) pectins, which do not need sugar or acid
to form gel, but instead calcium salt is used (Fellows, 1997).
Commercially low methoxyl pectins are used to make low fruit jams
and jellies (Pilnik and Voragen, 1970).
Pectins are used in many other products such as fruit
preparation for yogurt, fruit drink concentrate, fruit juice, fruit/milk
desserts and fermented and directly acidified dairy products.
Mohamed (1999) reported that pectin is also used in bakery products
in which jams are filled into tarts and biscuits.
Belo and Lumen (1981) who reviewed the work of several
authors reported that pectic substances have important physiological
and nutritional effects. There include hypocholesterolemic effect,
increased excretion of fecal sterols and lipids, binding of bile salts and
anti-diarrhea effect.
2.6.5. Sources of the pectic substances:
Pectic compounds are present in all fruits and vegetables (Matz,
1962, Searle et al., 1992). They are found in middle lamella of plant
cells (Matz, 1962; Owen, 1985). The pectic substances of fruit are
located in middle lamella as cementing material and on the cell wall
(Matz, 1962).
Searle et al. (1992) reported the content of pectic substances in
some fruits and vegetables such as grapes (0.2–1%), apples (0.5–
1.6%), lemon (3– 4%), lemon seeds (6%), grapefruit (1.6–4.5%) and
sugar beet pulp (30%). Kertesz (1951) showed pectin content of some
fresh fruits on fresh weight basis such as pears (0.5–0.7%), tomatoes
(0.1–0.5%) and banana (0.7 – 1.2%).
The production of highly polymerized pectin is largely
dependent upon the quality of pectic substances in sources material
(Baker, 1948) as well as methods of handling and storage of these byproducts previous to use (Baker, 1948).
All citrus contain pectin and the richest sources are limes,
lemons, oranges and grapefruit (Baker, 1948; Bates et al., 2001) and
pulp of apple (Fellows, 1997). Lime peel is an important source of
pectin containing 15– 30% pectin on dry weight basis (Padival et al.,
1979). Mohamed reported 2.6 gm/100gm pectin content from
grapefruit peels on fresh weight basis .Fruit such as apple contains
abundant pectin in cores and skin (Baker, 1948) whereas in citrus
fruits the pectin is chiefly in white part of rind (Hughes , 1964; Bates
et al., 2001).
Abdelrahman (2002) reported 0.35-0.78 % pectin content from
mango pulp. Mango peel is available in large quantities in mango
processing industry which could be of a very useful source of raw
material for extraction of pectin (Srirangarajan and Shrikhand, 1979).
El-shafie (1981) reported that the total pectin on fresh weigh of
pumpkin was 0.5%. Pectic substances have long been recognized as
an important constituent of tobacco. Numerous reports were reviewed
on their extraction and determination in tobacco leaf (Jacin et al.,
1967).
2.6.6. Properties of orange peel pectin:
Eaks and Sinclair (1980) reported a range of 18.2– 23.0% total
pectin from Valencia orange peel on dry weight basis. Belo and
Lumen (1981) found the total pectin of orange ablbedo to be 27.88%.
Elmubarak et al.
(1977) studied some properties of pectin from
orange and reported 7.16% moisture, 1.4% ash, 1474 equivalent
weight, 0.524% Acetyl content, 3.90% methoxyl content, 33.91%
anhydrogalacturonic acid, 1.03% calcium, 2.77 intrinsic viscosity and
5.00 x 104 molecular weight.
Eltinay et al., (1982) characterized the commercial citrus pectin
as follows: 5.18% moisture, 0.09% ash, 0.034% acetyl content, 66.9%
degree of esterification, 77.9% anhydrogalacuronic acid by carbazole
method and 72.8% by the titrimetric method, 3.87 meq/g total
carboxyl, 74.8 equivalent weight, 3.20 dl/g intrinsic viscosity and 5.57
x 104 average molecular weight.
CHAPTER THREE
MATERIALS AND METHODS
3.1. Materials:
3.1.1. Chemicals:
All chemicals and reagents, used in this study, were of
analytical grade.
3.1.2. Raw material:
Orange (yellow and green)samples were obtained from local
market. Peels of the two types were dried at room temperature (about
30ºC), ground, sieved and kept for further analysis.
3.2. Analysis of orange peels:
3.2.1. Proximate analysis:
Proximate analysis was done according to AOAC (1975) and
AOAC (1990). The parameters determined were moisture, ash, crude
protein, fats and crude fibers.
3.2.2. Alcohol insoluble solids (AIS):
AIS were determined according to AOAC method (1970) in the
manner described by Mohamed (1999). Twenty gram of materials
were weighed into 600 ml beaker. Three hundred milliliters of 95%
alcohol were added, stirred and brought to boiling. The mixture was
simmered slowly for 30 minutes and then filtered through a buchner
fitted with an approximate size filtered paper which was previously
dried in flat bottomed dish for 2 hours at 100ºC, covered with a tight
fit cover and weighed.
The residue was then washed with 80% alcohol until washings
were clear and coloureless. The paper was then transferred to the
previous dish and dried uncovered at 100ºC for 2 hours. The final
weight minus the filter paper weight was recorded as weight of
alcohol insoluble solids and its percentage was then calculated as
follows:
Percent AIS =
Final weight − filter paper weight
× 100
weight of sample
3.2.3. Titrable acidity:
The titrable acidity was estimated according to Board (1988)
method. Ten grams of material were homogenized in a blender and the
volume made up to 250ml with distilled water and filtered. One
hundred milliliters aliquouts
were taken and titrated with 0.1N
sodium hydroxide to pH 8.0 using phenolphthalein as indicator. The
results were expressed as percent citric acid as follows:
Titrable acidiy % = No. of ml of 0.1N NaOH × c.f.
c.f. : conversion factor which is equal to 0.07 citric acid hydrous.
3.2.4. Ascorbic acid content:
Ascorbic acid content was determined according to Ruck
method (1963) in the manner described by El-obeid (2003). Thirty
grams of the sample were blended with about 100ml of 0.4% oxalic
acid (4 grams/100ml) for two minutes in a blender. The blended
mixture was made up to 500ml in a volumetric flask with 0.4% oxalic
acid and filtered. The ascorbic acid in the filtrate was determined by
titrating 20ml of the filtrate against 2,6-dichlorophenol indophenol
(0.2g/500ml distilled water) of known strength. Ascorbic acid,
expressed in mg/100g dry matter, was calculated as follows:
Titer ( ml) × dye strength × 100
factor
Sample weight × sample volume taken for titration
total volume of the sample
Ascorbic acid (mg/100g) =
Where the factor =
Dye strength = 1/titre.
The dye was standardized as follows:
50mg of standard ascorbic acid were weighed and made up to volume
by 10% oxalic acid in a 250 volumetric flask and 5ml a liquid was
diluted with 5ml 10% oxalic acid (50grams oxalic acid/500ml distilled
water) and titred with the dye solution to a pink end point.
3.2.5. Sugars:
3.2.5.1. Reducing sugars:
Reducing sugar were determined by modified method of Lane
and Eynon as described by Schneider (1979). Ten grams were
extracted with 200ml ethanol (70%) for 6 hours in a soxhelt apparatus.
The solution was then evaporated to 100ml, clarified by adding lead
acetate (2ml) and filtered. Sodium oxalate (2g) was added to remove
the lead acetate by filtration. The burrette was filled with solution
prepared above. Fifteen milliliters of this solution were run into a ten
milliliters fehling solution, mixed well and heated to boiling on an
electric heater. The solution was kept boiling for 2 minutes and then 3
drops of methylene blue indicator (1gm/100ml distilled water) were
added. The titration was completed by addition of sugar solution (drop
by drop) until the colour of indicator disappeared and red-brick colour
appeared. The reducing sugar were calculated from the table (Pearson,
1970) according to the following equation:
Reducing sugar = mg of sugar / 100ml of solution × dilution factor × 100
1000 × weight of sample
3.2.5.2. Total sugars:
The total sugars were determined according to the method
described by Mohamed (1999). Ten milliliters of HCl :H2O (1 : 1)
were added to 50mls sugar extract and left for 8 hours. The solution
was neutralized by NaOH (40%), the volume was completed to 100ml
and titrated against fehling solution as mentioned above. Total sugars
were calculated according to the following equation:
Total sugars =
mg of sugar / 100ml of solution × dilution factor ×100
1000 × weight of sample
3.2.6. Calcium and magnesium:
Calcium and magnesium were determined according to the
method described by Pearson (1976) with some modifications.
One gram sample was put in a procelin crucible, placed in a
muffle furnace and ashed at 600º C overnight. the ash was dissolved in
slight excess of dilude nitric acid, transferred to a 50ml volumetric
flask and made up to mark with water.A volume of the solution
containing 3 – 12 mg of calcium was piptted in to flask , diluted to
50ml, neutralized with M sodium hydroxide and 5ml in excess were
added to produce a pH of 12. Murexide (0.2gm ) was added and
titrated with versenate solution and stirred throughout the colour
change at the end-point from red to violet red.
To determine magnesium content. The above solution was
titrated at pH 10 after making alkaline with ammonium chloride and
ammonium hydroxide buffer and Eriochrome Black T was used as
indicator.
3.3. Preparation and Analysis of Alcohol insoluble Solids:
3.3.1. Preparation of alcohol insoluble solid(AIS):
AIS were prepared according to the method of Luth et al.
(1960) in the manner described by Mohamed (1999). The Orange
powder was added to 400ml boiling ethanol (95%) in a wide mouth
flasks and boiled for ten minutes. The contents were filtered through
filter paper N 0.1 (under suction), washed with sufficient 70% alcohol
to remove sugars followed by 95% alcohol to remove other interfering
substances and dried at room temperature (about 30ºC). These were
ground to pass through 60-mesh and kept in a labeled bottle for further
analysis.
3.3.2. Analysis of alcohol insoluble Solids:
3.3.2.1. Proximate analysis:
To determine the chemical component of the alcohol insoluble
solids,
standards
A.O.A.C
methods
(1970)
was
used.
The
determination was carried out in triplicate. The components
determined were moisture, ash and crude protein.
3.4. Isolation of orange peels pectins:
The method of Change and Smith (1973) with some
modification was adopted for isolation of total pectic material from
orange peels. Hundred grams of alcohol insoluble solids were
suspended in 1500ml distilled water and thoroughly mixed. The pH
was adjusted to 2.0 with conc. Hydrochloric acid and the mixture was
left for30 minutes at room temperature .The mixture was heated in a
water bath at 100ºC and left at that temperature for 60 minutes. After
cooling the extract was recovered by centrifugation at 3000 rpm for 15
minutes. The cake was suspended in 60ml distilled water, acidified to
pH 2.00 with conc. Hydrochloric acid, heated at 100°C in a water bath
for 10 minutes and centrifuged again. The liquid recovered was
bulked with the first extract before filtering under vacuum through a
very rapid qualitative filter paper. The clear filtrate was added to two
volumes of 95% ethanol with stirring and left for 12 hours to allow
precipitation and Hardening of the pectic material. The precipitated
pectic material was recovered on cheese cloth and then washed twice
by suspending in 1000 ml 80% ethanol. These suspensions were left
for an hour then washed with 95% ethanol followed by acetone. The
recovered crude pectin was left to dry in an oven at 60ºC. It was then
ground to pass through a mesh No. 60 and kept in labeled bottle for
further analysis.
3.5. Quantitative analysis of the isolated pectin:
The methods describe by Owens et al. (1952) and Mohamed
(1999) were used for the analysis of the isolated pectin.
3.5.1. Moisture:
Triplicate samples (1 gm ash), were weighed in dried and
weighed aluminum dishes. Samples were then dried for 4 hours at
105ºC (20mm Hg). They were then cooled in a desiccator and
weighed to constant weight . The moisture content was calculated as
followed:
Moisture % =
W1 − W2
×100
S
Where:
W1
= weight before drying.
W2
= weight after drying.
S
= weight of sample.
3.5.2. Ash:
Triplicate samples (1 gm each) were weighed into previously
ignited ,cooled and weighed crucibles. Samples were then ignited at
600ºC for 3 hours, cooled and weighed to a constant weight. The ash
content was calculated as follows:
Ash % =
W2 − W0
×100
W1 − W0
Where:
W0
= weight of empty crucible.
W1
= weight before ashing.
W2
= weight after ashing.
3.5.3. Ash alkalinity:
The ash prepared was dissolved in 25ml of 0.1N HCl, heated
gently and then titrated with 0.1 sodium hydroxide using
phenolphthalein indicator. The alkalinity number of an ash is
calculated as the number of milliliters of acid required to neutralized
one gram ash.
3.5.4. Equivalent weight:
Triplicate samples (0.5 gm each) of pectic substances were
weighed into 250ml conical flask and moistened with 5.0 ml ethanol.
The product was mixed with one gram sodium chloride and 100 ml of
distilled water. The mixture was stirred vigorously and free acidity
was determined by direct titration against 0.1N sodium hydroxide
using phenol red indicator. A blank containing the same quantities of
reagents was used. according to Owens et al., (1952).The equivalent
weight was calculated as follows:
Equivalent weight =
weight of sample ( mg)
meq of sodium hydroxide
Where:
Meq ( Milliequivalent of sodium hydroxide) =
normality × titre volume of NaOH
This titre is knowm as initial titre (IT) or free acid titre.
3.5.5. Methoxyl content:
To the neutralized solution obtained above, 25mls of 0.025N
NaOH were added. The mixture was shaken and allowed to stand in
stoppered flask at room temperature for 30 minutes. Twenty five
milliliters 0.025N HCl were added and the mixture was adjusted to pH
7.5. The titre was corrected for the reagent blank. This titre is known
as saponification titre (ST). The methoxyl content was calculated as
follows:
Methoxyl content % =
Meq of NaOH × 31× 100
weight of sample
Where:
Meq of NaOH = normality of NaOH × titre figure.
31 = formula weight of methoxyl group
From the IT and ST obtained the degree of esterification and
anhydrouronic acid (AUA) content were calculated as follows:
Degree of esterification (DE) =
ST × 100
ST + corrected IT
The IT was corrected for the ash alkalinity
Anhydrouronic acid (AUA) content =
176 ×100
Z
Where
Z=
Weight of sample
meq of alkali for free acid × meq of alkali for methoxyl
3.5.6. Acetyl content:
Acetyl content was determined according to the method adopted
by Pippen et al., (1950) in the manner described by Abdel-rahman
(2002). Triplicate samples (0.5 gm each) of pectin were weighed into
flask and 25ml of 0.1N NaOH were added. The flask was stoppered,
shaken and left overnight. The solution was then diluted to 50ml, from
which 20ml were taken and placed in a distillation apparatus. Twenty
milliliters magnesium sulphate sulphuric acid solution (100mg
magnesium sulphate and 1.5gm of sulphuric acid diluted to 180ml)
were added. The solution was then steam distilled and 100ml of
distillate were collected. The acetic acid in the distillate was then
titrated with 0.05N sodium hydroxide to phenol red end point. The
titre was corrected for the reagent blank. The acetyl content (formula
weight 43) of sample was calculated according to the following
equation:
Acetyl content (%w/w) =
(net ml of NaOH )(normality of NaOH ) × 4.3
weight of sample (gm) in the a liquot
Net ml of NaOH = volume of NaOH required to titre distillate –
volume of NaOH required to titre distillate of blank run.
3.5.7. Anhydrouronic acid (AUA) content:
AUA content was determined according to McCready and
McComb (1952).A solution of pectin of 0.1% concentration was deesterified by holding it in a solution of 0.05N sodium hydroxide and
diluted to 0.002%. Two milliters of this solution were added to 12 ml
of ice cooled concentrated sulphuric acid in a pyrex test tube. The
contents were heated in a boiling water bath for 10 minutes, cooled to
20°C and one ml of 0.15% carbazole in ethanol was added. The
contents were mixed thoroughly and left for 25 minutes before
colourimeteric determination of the colour intensity at wave length
520nm was made. A standard curve was constructed with known
amounts of galacturonic acid ranged from 0 to 3.5mg/2ml (Mohamed,
1999).
3.5.8. Viscosity:
Viscosity was determined according to the method of Owens et
al. (1952) as described by Mohamed (1999). A 0.1gm of pectic
substance was weighed into a beaker and 50ml of distilled water were
added and the pH adjusted to 4.8 with 0.1N NaOH. The solution was
stirred for 2 hours. Sodium chloride (0.8gm) and sodium
hexametaphosphate (0.2gm), known as calgon, in 15ml distilled water
were added and stirred for further hour. The pH was then adjusted to
6.0 with 0.1N acetic acid and the solution was transferred to a 100mls
volumetric flask and made to volume with distilled water. The
viscosity was determined within an hour using ostwald cannon –
Fenske No. 1098 at room temperature. The efflux time was
determined in the same instrument for the solvent (0.8 NaCl + 0.2%
calgon). The relative viscosity was calculated as the ratio of the time
of efflux for solution to that for solvent:
Relative viscosity (µr) =
time (solution)
time (solvent)
To determine intrinsic viscosity another three concentrations
(0.15, 0.10 and 0.05g/100ml) were prepared as mentioned above. The
relative viscosity was calculated .To get the intrinsic viscosity the
ratio (µr – 1)/c was plotted against C on semi log paper and
extrapolated to zero to get intrinsic viscosity where:
C = concentration.
µr = relative viscosity
The average molecular weight was determined from intrinsic
viscosity data according to the equation
N = 1.4 × 10-6M1.34
Where:
N = intrinsic viscosity
M = molecular weight.
3.6. Statistical analysis:
The data of this study was analyzed using a computer statistical
package of social science (SPSS) soft ware version 10.01. T-student
test was used to compare between yellow and green types of orange
peels.
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Chemical composition of orange peels:
The proximate composition of orange peels (yellow and green)
was determined and the results were presented in table 1. The results
were expressed on dry weight basis.
Chemical analysis revealed that the moisture contents were
6.72% for yellow and 7.92% for green. The results showed significant
difference (P < 0.05) between peels of the two orange types
investigated. Mohamed (1999) reported moisture content of grapefruit
peels to range between 75.25%and 75.37 and Morton (1987) obtained
72.5% moisture content of orange peels on fresh weight basis.
Ash contents of the two types were 2.59% and 1.84 %
respectively. A significant difference (p <0.01) was observed between
the two types under study. The values obtained in this work were
higher than 1.45 – 1.62 %. for grapefruit peels reported by Mohamed
(1999). Ash content values were reported to vary according to many
factors such as varietal difference, fertilizers applied, irrigation
practices and region (Nour et al. 1981).
Table 1: Analysis of orange peels grams / 100 grams (on dry weight
basis).
Peels of yellow
type
Peels of green
type
Level of significance
Moisture%
6.72a ± 0.38
7.92 b ± 0.69
*
Ash%
2.59a ± 0.25
1.84b ± 0.05
**
Protein
5.84a ± 0.27
6.65 b ± 0.29
*
Crude fiber%
8.30a ± 0.61
9.47 b ±0.11
*
Volatile oil %
3.08a ± 0.38
2.75 a ± 0.25
Ns
Titrable acidity%
0.43a ± 0.038
0.40a ±0.008
Ns
Ascorbic acid mg/100gm
60.09a ± 3.55
34.95 b ± 1.04
**
Reducing sugars %
11.01a ± 0.15
5.03 b ± 0.06
**
Total sugars %
16.62a ± 0.17
7.77 b ±0.05
**
Calcium mg/ 100gm
0.78a ± 0.03
0.83a ±0.02
Ns
Magnesium mg/100gm
0.19a ± 0.01
0.18a ± 0.01
Ns
Alcohol insoluble solids
50.55a ± 0.34
60.74 b ± 0.44
**
Analysis
ƒ
Values are means ± SD of 3 replicates for each parameter.
ƒ
Means within raw with same superscripts are not significantly
different.
ƒ
Ns=not significantly different.
ƒ
* =significant (p< 0.05).
ƒ
** =significant (p < 0.01).
Protein contents were 5.84 % and 6.65 % respectively. A
significant difference (p< 0.05) was observed between peels of the
two types.
Protein content of dry citrus peels(6%) reported by
Braddock and Crandall (1981) while Morton (1987) reported 1.54%
protein content of fresh orange peels. Differences in protein content
might be attributed to type of citrus and agricultural practices as well
as availability of nitrogen in soil.
Volatile oil values of the two types of orange peels were 3.08
and 2.75 % respectively. No significant difference was observed in the
two types of orange peels. The values obtained were located within
the range of 1.5- 6.50 % reported by Sinclair (1972) for citrus fruit
peels.
Crude fiber contents of the two types were 8.3 and 9.47
respectively. A significant difference (p< 0.05) was observed between
the two types. Crude fibre is the measure of cellulose and lignin
contents and is useful in measuring the quality of vegetables
(Mohamed, 1999).
Titrable acidity of the two types of peels were 0.43% and 0.40%
respectively. No significant difference was observed between the two
types.A scorbic acid content of the two types of peels were
0.06g/100g and 0.035g/100g respectively. A significant difference (p<
0.01) was observed between the two types. The results of this study
were lower than the values reported by Mohamed (1999) and Eaks
(1964), they found 0.15-0.185g/100g for grapefruit peels and orange
lemon peels respectively. Sanclair (1972) reported that the value of
ascorbic acid content was 0.142g/100g of grapefruit peels and also
disagree with the work of Morton (1987) who found 0.136g/100g for
orange peels on fresh weight basis. Kefford (1959) obtained that
ascorbic acid content ranged between 0.036 and
0.182g/100g of
orange albedo.
Reducing sugar values were 11.01% and 5.03% respectively. A
significant difference (p< 0.01) was observed between yellow and
green peels. The value of yellow type was higher if compared to the
range of 10.2- 10.4% reported by Mohamed (1999) for grapefruit
peels. The amount of soluble carbohydrates of peel and pulp of citrus
correlated with the stage of fruit maturity (Mohamed, 1999).
Total sugar contents of the two types, under study, were found
to be 16.62% and 7.77% respectively. A significant difference (p<
0.01) was observed between the two types .
Calcium
content
of
the
two
types
investigated
was
0.78mg/100gm for yellow and 0.83mg/100gm for green. No
significant difference was observed between the two types. These
values were located within the range of 0.55- 0.9mg/100gm obtained
by Dezman et al. (1984) for grapefruit peels, but higher if compared to
the range of 0.69- 0.71mg/10gm reported by Mohamed (1999) for
grape fruit peels.
Magnesium content of the two types was 0.19mg/100gm for
yellow and 0.18mg/100gm for green. No significant difference was
observed between the two types of orange peels. These results were
comparable to the range of 0.18-0.28mg/100gm reported by Dezman
(1984) for grapefruit peels and higher if compared to the value of
0.17mg/100gm reported by Mohamed (1999) for grapefruit peels.
Alcohol insoluble solids (AIS) of the two types were 50.55%
and 60.74% respectively. The results showed a significant difference
(p< 0.01) between the two types. These values were higher than the
value of 42.69% and the range of 38.0- 42% reported by Kefford
(1959) and Mohamed (1999) respectively.
4.2. Analysis of alcohol insoluble solids (AIS)
The chemical analysis results of AIS of yellow and green orange peels
were shown in table2. Moisture contents of the two types of AIS were
2.92% and 5.63 respectively. The result showed significant difference
(p< 0.01) between the types investigated. Mohamed (1999) reported
the moisture content of two types of AIS to be 7.05 and 7.17% for
grapefruit peels.
The ash contents were 4.09% and 4.48% respectively. No
significant difference was observed between the two types.
The protein contents of AIS for the two types were 7.65% and
7.49% respectively. Once again no significant difference was seen
between the two types.
Total pectin contents for the two types studied were 14.84% and
16.06% respectively. The results showed significant difference (P<
0.01) between the two types. These results disagree with the range of
25-25.26% reported by Mohamed (1999) for grapefruit peels and the
range of 20- 40% ( on dry weight basis) obtained for citrus peels,
reported by Doesburg (1965). The results obtained are comparable
with the findings of Alexander and Sulebele (1980) who reported a
range of 15- 17 %
pectic substance from Indian citrus peels. Iranzo
et al. (1980) reported a range of 12.4 – 44%. Pectic substance in
spainsh citrus peels. El.tinay et al. (1982) obtained 27.3-32.8% total
pectin from pumpkin AIS. Elmubark et al. (1977) obtained values of
4.29% (lime), 4.48% (orange) and 2.17 % (grapefruit) as total pectin
on fresh weight basis.
Table (2): Analysis of alcohol insoluble solids (AIS) in grams/ 100
grams ( on dry weight besis).
AIS of yellow
type
AIS of green
type
Level of
significance
Moisture%
2.92a ± 0.48
5.63b ± 0.12
**
Ash%
4.09a ± 0.05
4.48 b ± 0.20
*
Protein
7.65a ± 0.13
7.49 a ± 0.36
Ns
Total pectin %
14.84a ± 0.48
16.06 b ± 0.30
*
Calcium mg/ 100gm
0.22a ± 0.02
0.21a ± 0.01
Ns
Magnesium mg/100gm
0.12b ± 0.01
0.11b ± 0.03
Ns
Analysis
ƒ
Values are mean ± SD of 3 replicates for each parameter.
ƒ
Means within raw with same superscripts are not significantly
different.
ƒ
Ns= not significantly different.
ƒ
* =significant (p< 0.05).
ƒ
**= significant (p < 0.01).
Calcium contents of the two types of AIS were 0.22mg/ 100gm
(yellow peels) and 0.21mg/100gm (green peels ). No significant
difference was seen between the two types. Mohamed (1999) found
calcium contents of AIS from grapefruit peels to be in the range 1.04
to 1.83mg/100gm .Calcium content of pumkin AIS were shown to
range between 0.4 and 0.53 mg/100 gm (Eltinay et al., 1982).
Magnesium contents were 0.12mg/100gm (yellow peels) and
0.11mg/100gm (green peels). No significant difference was observed
between the two types. Mohamed (1999) reported magnesium
contents of AIS from grapefruit peels in the range of 0.170.19mg/100gm. Magmesium contents ranged between 0.09 and
0.11mg/100gm were obtained by El.tinay et al. (1982) for pumpkin.
4.3. properties of orange peels pectic substances:
Properties of orange peels pectic substances were determined
and their results were shown in table 3.
Moisture contents of the two types were 7.98% and 8.09%
respectively. No significant difference was observed between the two
types. The results are in conformity with the range of 7.88- 8.96% for
grapefruit peels pectin reported by Mohamed (1999) but, higher if
compared to the value of 7.16% reported by Elmubark et al. (1977)
for orange peels pectin. The values obtained in this study were also
higher than the range of 5.03- 7.04% reported by Abdelrahman (2002)
for mango pulp pectin and values of 5.04- 6.3% reported by Saeed
(1974) for some Sudanese mango pectin.
Ash content of the two types of peels was 3.10% and 3.37%
respectively. No significant difference was observed between the two
types. The present values fall within the range of 1.56 - 7.65 %
(lemon), 0.81- 4.83% (orange) and 0.49 - 8.05% (apple) cited by
Abdel-rahman (2002). El-mubark et al. (1977) reported values of
1.7% (lime), 1.40 %(orange) and 1.00% (grapefruit) for ash of pectin.
Mango pulp ash in the range of 1..26- 2.02 % was reported by
Abdelrahman (2002). The ash content of Indian citrus peels pectin
obtained by Alexander and Sulebele(1980) was 2.82 % (lime), 2.96 %
(orange), 2.85% (sweet orange)and 3.2% (grapefruit). El-tinay et al.
(1979) found ash content from 0.2% to 1% for guava pectin and
Mohamed (1999) reported from 1.8 % to 2.0 % for grapefruit peels
pectin.
Ash alkalinity of pectin was 1.5meq NaoH/gm and 1.49 meq
NaoH/gm for yellow and green peels respectively. No significant
difference was observed between the two types. Mohamed
(1999)found that the alkalinity of ash was 2.48 meq NaOH/gm and
1.56 meq NaOH/gm for grapefruit peels pectin. Ash alkalinity of
mango pulp pectin reported by Abdelrahman (2002) ranged between
2.04 meq Na OH/gm to 2.48 meq Na OH/gm. The ash alkalinity is the
measure of mineral constituents combined with organic acid groups.
Calcium pectate is probably one of the constituents of the cell wall
structure (Mohamed, 1999).
Protein values were 3.57 % and 3.44 respectively. No
significant difference was observed between the two types. These
values were higher than those obtained by Mohamed (1999) who
reported 0.0399- 0.0405 % protein for grapefruit peels pectin and
0.129% for commercial citrus pectin. Abdel-rahman (2002) reported
0.22- 0.34 % protein for mango pulp pectin. The values of protein
contents obtained by El-shafie (1981) were 1.24% (citrus pectin) and
4.2% (pumpkin pectin).
Acetyl content of the two types was 0.44% and 0.46%
respectively. No significant difference was seen between the two
types. These results were inline with the finding of Mohamed (1999)
who reported 0.46- 1.63% for grapefruit peels pectin and 0.63 % for
commercial citrus pectin and also agreed with the results of El-mubark
et al. (1977) who reported 0.43 % (lime), 0.524 % (orange) and 0.55
(grapefruit). Alexander and sulebele (1980) found that the acetyl
content of some citrus peels pectin ranged between 0.32 % and 0.46
%. Abdelrahman (2002) reported values from 0.117 % to 0.314 acetyl
content in mango pulp pectin. Saeed (1974) reported acetyl content
from 0.412 % to 0.55 % for mango marc. The acetyl group in pectin
substances have significant role on account of their effect on the jelly
forming ability (Abdelrahman, 2002).
Methoxyl contents of the two types of orange were 8.95 % and
8.89 % respectively. These results showed no significant difference
between the two types. These values agreed with the results obtained
by Mohamed (1999)who reported 8.875 % for grapefruit peels pectin
and El-shafie (1981) who reported 8.82% for citrus pectin , but higher
if compared to the range of 3.9- 4.11 % reported by El-mubark et al.
(1977) for citrus pectin, 2.71- 4.13 reported by El-tinay et al. (1978)
for guava pectin, 5.72 % reported by Sinclair and Grandall (1949) for
grapefruit peels pectin and 7.40- 8.62 % obtained by Alexander and
Suelbele (1980) for some citrus pectin.The methoxyl content is an
important factor in evaluating the setting time of pectin, sensitivity to
polyvalent cations and their usefulness in low solids gels, films and
fibre (El-tinay et al., 1979).It is generally true that an increase in
methoxyl content and decrease in the molecular weight will decrease
the jelly grade. The difference in methoxyl content were far outweighted by the large difference in molecular weight (Change and
Smith, 1973).
Tables 3: Properties of orange peels pectic substances:
pectin of
pectin of
Level of
yellow type
green type
significance
Moisture%
7.98 ± 0.13
8.09 ± 0.28
Ns
Ash%
3.14 ± 0.14
3.37 ± 0.13
Ns
Ash alkalinity meg Na OH/gm
1.50 ± 0.02
1.49 ± 0.04
Ns
Protein
3.57± 0.23
3.44 ± 0.27
Ns
Acetyl content
0.44 ±0.07
0.46 ±0.07
Ns
Methoxyl content
8.95 ± 0.32
8.87 ± 0.11
Ns
Free carboxyl group meq/gm
0.51 ± 0.02
0.54 ± 0.15
Ns
Esterified carboxyl group meq/gm
1.45 ± 0.05
1.43 ± 0.02
Ns
Total carboxy group meq/gm
1.96 ± 0.04
1.98 ± 0.02
Ns
Anhydro lacturonic acid(c)
76.57 ± 1.25
76.16 ± 1.10
Ns
Anhydro lacturonic acid (T)
68.99 ± 1.41
69.46 ± 0.62
Ns
Equivalent weight
974.60 ± 28.74
920.73 ± 25.67
Ns
Calcium mg/ 100gm
0.28 ± 0.02
0.30 ± 0.01
Ns
Magnesium /100gm
0.09 ± 0.01
0.07 ± 0.01
Ns
Degreeof slerificant ion
73.80 ± 1.07
72.47 ± 0.71
Ns
Intrinsic viscosity dI / gm
2.21± 0.77
2.09 ± 0.43
Ns
Average molecular weight
4.2 ×104
4.03 ×104
Ns
Analysis
ƒ
Values are means ± SD of 3 replicates for each parameter.
ƒ
Ns: not significant different (P > 0.05).
ƒ
C: Carbozole Method.
ƒ
T: Titrimetric method.
Free acidity of pectin obtained from the two types of orange
peels was 0.513meq/gm and 0.54 meq/gm respectively. No significant
difference was observed between the two types. Abdelrahman (2002)
found that free acidity was 0.72- 0.84 meq/gm for mango pulp pectin.
Esterified carboxyl group of the two types pectin was 1.447 meq/gm
and 1.433 meq/gm respectively. The total carboxyl groups of the two
types of pectin were 1.96meq/gm and 1.977 meq/gm respectively. No
significant difference was observed between the two types in
esterified carboxyl groups. The total carboxyl groups , obtained in this
study, lies within the higher values from 1.143 meq/gm to 1.23
meq/gm obtained by Abdel-rahman, 2002) for mango pulp pectin and
from 0.33 meq/gm to 0 .46 meq/gm reported by El-tinay et al. (1979)
and lower if compard to a range 1.52- 2.05 meq/gm reported by
Mohamed (1999) for grapefruit peels pectin and 3.87 meq/gm
obtained by El-shafie (1981) for citrus pectin. El-tinay et al.(1978)
showed that addition of calcium ions caused a decrease in the free
carboxyl group
content in guava pectin .The carboxyl groups
influence the viscosity of pectin solution depending upon the degree
of esterification. Solution of fully esterified pectin don’t change
appreciably in viscosity with change in pH, but when they contain
pectin of lower degree of esterification the viscosity becomes
markedly pH dependent (Abdel-rahman, 2002).
Anhydrouronic acid (AUA) content obtained by titrimetric
method for the two types of pectin was 68.99 % and 69.46 %
respectively. No significant difference was observed between the two
types. The values of AUA contents, obtained by Carbazole Method,
were 76.57% and 76.16% respectively. Mohamed (1999) reported that
the value of AUA content for grapefruit peels and commercial citrus
pectin were 60.95 % and 68.90 % respectively. The values obtained
were lower than that obtained by El-shafie(1981) and Kefford (1959)
who reported 77.86 % for citrus pectin and 80.85 % for commercial
citrus pectin respectively, but fall within the range of 73.9- 77.4 % for
some citrus pectin reported by Alexander and sulebele (1980).
Srirangajan and Shrikhande (1979) reported AUA content of 83.5 %
for orange, 59.4 % for apple and 61.12 % for mango. The results , in
this study, were higher than that obtained by El-mubark et al. (1977)
who reported 33.43 % (lime), 33.9 % (orange) and 32.94 %
(grapefruit) and abdelrahman (2002) who reported a range of 18.51526.0 % for mango pulp pectin. The quality of pectin is known to
depend upon the content of anhydrouronic acid and methxyl group
and also the degree of esterification ( Srirangarajan and Shrikhande,
1979). Good quality commercial preparations usually contain not less
than 68 % uronic acid. The AUA is the most significant property of
pectin. The properties of pectin are better described by the
polygalacturonic acid (Mohamed, 1999).
Equivalent weights for the two types varied from 920.73 to
974.60. No significant difference was seen between the two types.
These values are higher than the range of 620- 749 reported by
Mohamed (1999) for grapefruit peels pectin and the value of 749
found by El-shafie(1981) for citrus pectin. The equivalent weights,
obtained in this study ,were lower than range of 1389- 2003 reported
by Abdelrahman (2002) for mango pulp pectin and the values of 1751
(lime), 1474 (orange) and 1690 (grapefruit) reported by El-mubark et
al. (1977).
Calcium content of the two types of pectin were 0.28
mg/100gm and 0.30 mg/100gm respectively.Magnesium contents
were 0.087 mg/100gm and 0.07 mg/100gm respectively. These values
showed no significant difference between the two types in both
calcium and magnesium contents .Abdelrahman (2002) reported the
calcium and magnecium contents of mango pulp pectin to be 0.0020.004 mg/100gm and 0.820- 0.825 mg/100gm respectively. Mohamed
(1999) reported that the calcium content of grapefruit peels pectin
ranged between 0.55mg and 0.74mg/100gm and that of citrus pectin
was 0.24 mg/10gm. Magnesium content of 0.05 mg/100gm for
grapefruit peels pectin and 0.03 mg/ 100gm for commercial citrus
pectin was reported by Mohamed (1999).
Degree of esterification of the two types studied was 73.80 %
and 72.49 % respectively. The results showed no significant
difference between the two types. These results were higher than that
obtained by Mohamed (1999) for grapefruit peels pectin, zitco and
Bishop (1965) for citrus pectin, Alexander and Sulebele (1980) for
some citrus and El-tinay et al. (1982) for citrus pectin who reported
51.01- 51.24%, 67.0 %, 56.1- 63.2 % and 66.9 % respectively. The
values of this study are lower if compared to the range of 73.9- 86.8 %
for pumpkin pectin reported by El-tinay et al. (1982), 76.0 % reported
by Srirangarajan and Skrikhande (1977) for mango peels pectin and
87.0 % reported by Abdelrahman (2002) for mango pulp pectin.
The intrinsic viscosities for pectin were 2.707 dI/ gm and 2.09
dI/gm
for yellow and green peels respectively. No significant
difference was observed between the two types. These values are
lower if compared to the value of 3.30 dI/gm for commercial citrus
pectin (Nour, 1977), a range of 3.2 – 4.4 dI/ gm for some citrus pectin
(Alexander and Sulebele, 1980), 3.8dI/ gm for commercial citrus
pectin (Mohamed,1999) and the value of 3.9 dI/gm for citrus pectin
(Pippen et al., 1950). The values are higher than that obtained by
Abdelrahman (2002) for mango pulp pectin, Mohamed (1999) for
grapefruit peels pectin and Saeed et al. (1974) for some varieties of
mangoe pectin who reported 0.86- 1.43 dI/ gm, 1.5dI /gm and 0.601.22 dI/gm respectively. These results fall within the range of 0.755.9 dI/gm reported by Fishman et al. (1991) for some fruits and
vegetables.
The average molecular weights of the two types were 4.2x 104
and 4.03x 104 respectively. The average molecular weight of
grapefruit peels pectin reported by Mohamed (1999) was 3.162× 104.
The present values disagree with the range of 2.0877× 104- 3.0512×
104 reported by Abdelrahman (2002) and were higher than that
obtained by Saeed et al. (1974)for mango pectin who obtained
1.6×104- 2.1× 104. These values are lower if compared to values
reported by El-shafie (1981), Mohamed (1999) and El-tinay et al.
(1982) for citrus pectin who reported 5.951× 104, 5.038× 104 and
5.57× 104 respectively.
4.4. Conclusions and recommendations:
4.4.1. Conclusions:
This study was intended to investigate the proximate
composition, alcohol insoluble solidsfor orange peels and isolation
and characterization of the pectic substances. Two types of orange
peels, yellow and green, were used in this investigation.
Proximate chemical composition (moisture, ash calcium and
magnesium), protein and volatile oil, titrable acidity, ascorbic acid,
sugar and alcohol insoluble solids were determined. Alcohol insoluble
solid of the two types of orange peels were 50.55% and 60.74%
respectively. these values are comparable with the 38 -42% alcohol
insoluble solid
from grapefruit peels reported from literature. Total
pectin contents for the two type of orange peels were 14.74% and
16.06% respectively. Significant differences were observed between
the two types of orange peels, except for calcium, magnesium and
acidity.
The pectic substances were characterized and assessed for
,moisture, ash, ash alkalinity, protein, acetyl content, methxyl content,
carboxyl content, degree of esterification, anhydrogalacturonic acid,
equivalent weight, calcium, magnecium, intrinsic viscosity and
average molecular weights. No significant differences were observed
between the two types of orange peels pectin. Methoxy contents of
8.95% and 8.89% were obtained from yellow and green types
respectively. Degree of etherification obtained in this study were
73.80% and 72.47% for yellow and green types respectively. these
values comparable with the range of 73 – 86.8% for pumpkin pectin
obtained from earlier work. From the results, obtained in this study,it
can be concluded that the quantity and quality of pectin obtained from
orange peels (both yellow and green ) are suitable for commercial
production of pectin.
4.4.2 RECOMMENDATIONS:
Since the quantity and quality of pectin obtained from peels are
suitable for the commercial production of pectin, further work is
needed in this regard .This include:
1.
Economic feasibility of producing pectin from orange peels.
2.
Modification of the pectin extraction procedures
application.
3.
Trial of functionality of extracted pectin.
for easy
REFERENCES
A.O.A.C. (1970). Association of official analytical chemists. Official
Methods of analysis. 11th ed. Washington, DC.
Abdel-Rahman, N. A. (2002). Characterization of pectic substances of
abu-samaka cultivar in relation to their influence on mango
pulp concentrate M. Sc. Thesis. University of Khartoum.
Alexander, M. M. and Sulebele, G. A. (1980). Characterization of
pectin from Indian citrus peels. J. Fd. Sci. Technol. 17: 180
– 182.
A.O.A.C. (1975). Association of Official Analytical Chemists,
Official methods of Analysis, Washington. DC.
A.O.A.C. (1990). Association of Official Analytical Chemists,
Official methods of Analysis, Washington. DC.
Aspinall, G. O.; Graig, J. W. and Whyte, J. A. (1968). Lemon peel
pectin. Fractionation and partial hydrolysis of water soluble
pectin. Carbohydrate Res. 7: 442.
Baker, G. L. (1948). High-polymer pectins and their deesterification.
Adv. In food Research Vol. 1. pp 395 – 429. Academic
Press, INC, publisher, New York.
Bates, R. P.; Morris, J. R. and Grandall, P. G. (2001). Principles and
practices of small and medium scale fruit juice processing.
FAO Agric. services Bulletin 146.
Batisse, C.; Buret, M. and Coulomb, Ph. J. (1996). Biochemical
differences in cell wall of cherry fruit between soft and crisp
fruit. J. Agric. Food chem. 44:453 – 457.
Belo, P. S. and Lumen, B. O. (1981). Pectic substance content of
detergent-extracted dietary fibers. J. Agric. Food Chem.. 29.
(2) :370 – 373.
Board, P. W. (1988). Quality control in fruit and vegetable processing
.FAO Food and Nutrition.pp 20,39.
Bonner, J. (1936). The chemistry and physiology of pectin. Bot. Rev.
2: 475.
Boothby, D. (1980). The pectic components of plum fruits.
Phytochem. 19: 1949 – 1953.
Braddock, R. J. and Crandall, P. G. (1981). Carbohydrate fiber from
orange albedo. J. of Food Sci. 46.
Braddock, R. J. and Kesterson, J. W. (1974). Stabilization of
carotenoids in dried citrus flaved. J. Food Sci. 39: 712.
Burns, J. K.; Pressey, R. (1987). Calcium in cell walls of ripening
tomato and peach. J. Am. Soc. Hortic. Sci. 112(5): 783 –
787.
Change, Y. S. and Smith, J. B. (1973). Characterization of peach
pectins. J. Food. Sci. 39: 646 – 648.
Dezman, D.; Nagy, S. and Rouseff, R. (1984). Mineral composition of
marsh grapefruit peel during maturiation. Hort. Sci. 19(5):
654 – 655.
Doesburg, J. J. (1965). Pectic substances in fresh and preserved fruits
and vegetables. Commun, No. 25. Wageningen, Netherlands
(cited from Mohamed ,1999).
Eaks, I. L. and Sinclair, W. B. (1980). Cellulose-hemicellulose
fractions in the alcohol insoluble solids of Valencia orange
peel. J. Food Sci. 45: 985.
El Tinay, A. H.; El-shafie, A. S. and Nour, A. A. (1982). A chemical
study of pumpkin pectic substances Dep. Of Bio. Faculty of
Agriculture, University of Khartoum, Sudan.
El Tinay, A. H.; Saeed, A. R. and Bedri, M. F. (1979). Fraction and
characterization of guava pectic substances J. Fd. Technol.
14: 343 – 349.
El-hassan, A. M. (1989). A study of the effects of salinity and sodicity
on the nutrient status and yield of foster grapefruit. M. Sc.
Thesis, University of Khartoum, Sudan.
El-Mubarak, A.; Magboul, B. I. and Ali, A. M. (1977). Utilization of
citrus waste as a source of pectin in jam making. Sudan J.
Fd. Sci. Technol. 9: 55– 59. Food Research Centre,
Shambat, Sudan.
El-Obeid, S. M. (2003). A biochemical study on dehydrated whole
limes (Citrus aurantifolia) for export. M. Sc. Agric. Food
Science and Technol. Dep. Faculty of Agriculture,
University of Khartoum, Sudan.
El-Shafie, A. S. (1981). Isolation, fractionation and characterization of
pumpkin pectic substances. M. Sc. Thesis, University of
Khartoum, Sudan.
Fellows, P. (1997). Guidelines for small-scale fruit and vegetable
processors. FAO Agric. Services Bulletin 127, Rome.
Fils-Lycaon, B. and Buret, M. (1990). Loss of firmness and changes in
pectic fractions during ripening and over ripening of sweet
cherry. Hort. Sci. 25(1): 777 – 778.
Fishman, M. L.; Gillespie, D. T.; Sondey, S. M. and El Atawy, Y. S.
(1991). Intrinsic viscosity and molecular weight of pectin
components. Carbohydrate research. 215 (1): 91 – 104.
Foglitti, M. J. and Percheron, F. (1968). Identification of aldobiuronic
acid in some plant species. Charbohydrate Res. 7: 146.
Hamid, G. A.; Sidahmed, O. A. and Genief, A. A. (1999). Evaluation
of some sweet orange cultivars under the heavy clay
conditions of central Sudan. Sudan J. Agric. res. 2: 85 – 88.
Howard, L. R.; Buescher, R. W. (1990). Cell wall characteristics and
firmness of fresh pack cucumber Pickles effected by
pasteurization and calcium chloride. J. Food. Biochem. 14:
31 – 43.
Hughes, O. (1964). Introductory foods. 4th edition, New York.
Iranzo, R. J.; Barandalla, P. and Miralles, M. C. (1980). Preparation of
dried peel for pectin production from verities of mandarin,
grapefruit, bitter orange and lemon grow in spain Revista de
Agroguimicay Technologin de Alimentes 20(13): 339 –
402.
Jacin, H.; Moshy, R. J. and Fiore, J. V. (1967). Characterization of
pectic substances in Tobacco stems. J. Agric. Food Chem.
15(6): 1057 – 1063.
Janick, S.; Robert, W.; Frank, W. and Ruttan, V. W. (1981). Plant
science: An introduction to world crops. 3rd edn., W. H.
Freeman and Company, San Francisco Sco. California.
Jimenez, A.; Guillen, R.; Sanchez, C.; Fernandez-Bolanos, J. and
Heredia,
A.
(1996).
Molecular
weight
and
ionic
characteristics of olive cell wall polysaccharides during
processing. J. Agric. Fd. Chem. 44: 913 – 918.
Kefford, J. F. (1959). The chemical constituents of citrus fruits. Adv.
In food Res. Vol. 9.
Kefford, J. F. and Chandler, B. V. (1970). The chemical constituents
of citrus fruits.
Kerlesz, Z. I. (1951). The pectic substance. Interscience publisher,
New York.
Kesterson, J. W. and Braddock, R. J. (1976). By-products and
speciality products of Florida citrus. Univ. of Fla. Agric.
Exp. Stn. Gainesville, Fla. Techn. Bull. 784.
Kotschevar, L. H. (1961). Quality food purchasing. New York,
London.
Labaneiab, M. E.; Abou-Donia, S. A..; Mohamed, M. S. and El
Zalaki, E. M. (1979). J. Fd. Technol. 14: 95 – 100.
Labelle, R. L. (1971). Heat and calcium treatments for firming red tart
cherries in hot – fill process. J. Food. Sci. 36(2):323 – 326.
Lidster, P. D.; Porrit, S. W. and Tung, M. A. (1978). Texture
modification of van sweet cherries by post harvest calcium
treatments. J. Am. Soc. Hortic. Sci. 103(4), 527 – 530.
Luth, B. S.; Postmayer, H. S. and Leonard, S. J. (1960). Chemical and
colour changes in canned tomato ketchup. Food Technol.
15(5): 52.
Marchiner, H. (1986). Mineral nutrition of higher plants. Academic
Press, London, UK.
Matz, S. A. (1962). Food texture. The Avi. Publishing company, INC,
London.
McCready, R. M. and McComb, E. A. (1952). Extraction and
determination of total pectic materials in fruits. Anal.
Chem..24(12) 1986- 1988.
McCready, R. M. (1970). Pectin. Method in food analysis. Academic
Press, New York, London.
Mcphee, J. (1967). Orange Farar, status and Giroux, New York.
Mohamed, H. A. (1999). Extraction, fractionation and characterization
of pectic substances of grapefruit peels. M. Sc. Thesis,
University of Khartoum, Sudan.
Monselise, Sh. P. (1980). Handbook of fruit set and development.
CRC Press, INC. Baca Raton, Florida.
Morton, J. (1987). Fruits of warm climates. Juliaf. Miami, Fl. P. 134 –
142.
Nelson, Ph. E. and Tressler, D. K. (1980). Fruit and vegetable juice
processing Technology. 3rd edition. The Avi Publishing
company. INC.
Nour, A. M. (1977). A chemical study of the pectic substances
isolated from mango fruits, Ph. D. Thesis, Leads University
(cited from Nour, 1978).
Nour, A. M. (1978). The influence of pectic substances on textural
properties of mango fruits. Sudan J. Fd. Sci. and Technol.
Nour, A. M.; Abdel-Gayoum, A. A. and El-Mubarak, A. (1981).
Elimination of precipitate on concentrate orange drinks
product in Sudan. Sud. J. Fd. Sci. Technol. 13, Food
Research Centre, Shambat, Sudan.
Nso, E. J.; Ndibewu, P. and Kayem, G. J. (1988). Reduction of
viscosity of guava pulps by treatment with pectinases. Cam.
Biosc. Proc. 5: 412 – 420.
Owen, F. (1985). Food chemistry. 2nd edition.
Owens, H. S.; McCready, R. M.; Shepherd, A. D.; Schultz, T. H.;
Pippen, E. L.; Swenson, H. A.; Miers, J.C.; Erlandsen, R. F.
and Maclay, W. D. (1952). Methods used at western
regional research Laboratory for extraction and analysis of
pectin material. AIC 340. Albany, Calif. (Cited from
Abdelrahman, 2002).
Padival, R. A.; Ranganna, S. and Manjrekar, S. P. (1979). Low
methoxyl pectins from lime peel. J. Fd. Technol. 14: 333 –
342.
Pearson, D. (1970). The chemical analysis of food. J. A. Churchhill.
104 Gloucesster, Place London.
Pearson, D. (1976). The chemical analysis of foods, 7th edition.
Churchill Livingstone, Edinburgh London and New York.
Pilink, W. and Voragen, A. G. (1970). Pectic substance and other
uronides. Dep. of food Science, state agric. University,
Wagening, The Netherland, Academic Press, New York,
London.
Pippen, E. L.; Mccready, R. M. and Owens, H. S. (1950).
Determination of acetyl in pectin. Anal. Chem. 22(11): 1457
– 1459.
Ruck, J. A. (1963). Chemical method for analysis of fruit and
vegetable products. Dep. Of Agric. Canada.
Saeed, A. R. (1974). Physical and biochemical studies on factors
influencing quality of mango fruit nectar Ph. D. Thesis,
University of Khartoum, Sudan.
Saeed, A. R. and El Mubarak, A. (1974). Guide to jam manufacture of
industry. Food. Research Centre, Shambat, Sudan.
Schneider, F. (1979). Sugar analysis. Peteroboroughl, England.
Searle, M. J.; Brock, H. A.; Schols, G. B. and Voragen, A. G. (1992).
Rhamnogalacturonan acetyl esterase: a novel enzyme from
Aslergillis aculeatus, specific for the deacetylation of hairy
(ramified) regions of pectins. Applied microbiology and
biotechnology 58: 347 – 349.
Sinclair, W. B. and Crandall, P. R. (1949). Carbohydrate fractions of
grapefruit peel-Bot. Gaz. 111: 153.
Sinclair, W. B. and Crandall, P. R. (1953). Polyuronides fraction and
insoluble carbohydrates of orange peel. Bot. Gaz. 115: 162.
Sinclair, W.B. (1972). The grapefruit composition physiology and
products University of Calf.
Smits, T. S.; Beekhuizen, J. G.; Dijk, C. V.; Voragen, A. G. and
Recourt, K. (1995). Cell wall dissolution during industrial
processing of green beans. J. Agric. Food chem. 43: 2480 –
2485. American chemical society.
Solley, P. G. (1997). Citrus-limes, limes, oranges, tangerines,
grapefruit
and
pomelos.
http://www.soupsong.com/fc/iturs.htm
Soost, R. K. and Roose, M. L. (1996). Citrus. Fruit breeding. 1: 257 –
323.
Spiegel-Roy, P. and Goldschmid, E. E. (1996). Biology of citrus.
Cambridge University Press, Cambridge, England.
Srirangarajan, A. N. and Shrikhande, A. J. (1979). Comparative
aspects of pectin extracted from the peels of different
varieties of mango. J. Fd. Technol. 14: 539 – 541.
Ting, S. V. and Attaway, J. A. (1971). Citrus fruits. The biochemistry
of fruits and their products. Vol. 2 pp 107 – 169. Academic
Press, New York and London.
Tressler, D. K. and Joslyn, M. A. (1961). Fruit and vegetable juice
processing technology. The Avi publishing company, INC.
Whistler, R. L. and Smart, C. L. (1953). Pectic substances.
Polysaccharide chemistry. Academic Press, New York P.
161.
Wilson, C. W.; Bissett, O. W. and Berry, R. E. (1971). Three types of
citrus peel waste as sources of colour. J. Fd. Sci. 36: 1033.
Zitco, V. and Bishop, C. T. (1965). Fractionation of pectins from
sunflowers, sugar beets, apple and citrus fruits. Can. J.
Chem. 43: 320b.