1. food and drink
2. food
3. grains and pasta

STUDY ON MALTING CONDITION OF
MILLET AND SORGHUM GRAINS AND THE
USE OF THE MALT IN BREAD MAKING
By
Amani Ali Mohamed Elshewaya
B.Sc.(Agric.)
Faculty of Agriculture
University of Khartoum
Khartoum – Sudan (2001)
Thesis submitted to the University of Khartoum in
Partial fulfillment of the requirements for the Degree
Master of Science (Agric.)
Supervisor,
Prof. Abdelmoneim Ibrahim Mustafa
Department of Food Science and Technology
Faculty of Agriculture
University of Khartoum
2003
DEDUCATION
To my family with love,
To my friends with respect
ACKNOWLEDGEMENT
I would like to express my sincere appreciation and
gratitude to my supervisor Prof. Abdel Moneim Ibrahim Mustafa,
Faculty of Agriculture, Department of Food Science and Technology,
University of Khartoum for his supervision, helpful, advice and
encouragement
Deep sense of gratitude is expressed to Dr. Babiker Elwasila
Mohamed, Faculty of Agriculture, Department of Food Science and
Technology, University of Khartoum, Prof. Abdel Halim Rahma,
Director of Food Research Centre, Dr. Maymona Mubarak, Industrial
Research and Consultancy Institute for their continuous help.
My deepest appreciation of gratitude is expressed to Dr. Abu
Elgasim Yaghou, Zalinge University for his criticism advice,
encouragement and beautiful help that enable me to present this study.
Deep thank are due to the staff members of the Food Research
Centre, Industrial Research and Consultancy Institute, Shambat
Laboratory.
Special appreciation to Dr. Abdalazeem Yassin, Faculty of
Forestry, University of Khartoum for his unlimited assistance in
analyzing the data of the thesis.
It is impossible to name all those good friends whom
encouraged me, I can only say, thank you to all.
List of Contents
Page
Dedication
i
Acknowledgement
ii
List of Content
iii
List of Table
vii
List of Figure
viii
List of Plate
ix
Abstract
x
Arabic Abstract
xii
1
CHAPER ONE: INTRODUCTION
3
CHAPTER TWO: LITERATURE REVIEW
2.1
Wheat Composition
3
2.1.1
Moisture content
4
2.1.2
Ash content
5
2.1.3
Protein content
5
2.1.4
Fat content
6
2.1.5
Fiber content
6
2.1.6
Starch
7
2.1.6.1
Variation in starch molecules for different crop
7
2.1.6.2
Gelatinization of starch
8
2.1.6.3
Non carbohydrate constituents of starch
9
Hydrolysis of wheat starch and its effect on 10
2.1.6.4
falling number
2.2
12
Sorghum and millet
2.2.1
Sorghum composition
12
2.2.1.1
2.2.1.2
2.2.1.3
2.2.1.4
2.2.1.5
2.2.2
2.2.2.1
2.2.2.2
2.2.2.3
2.2.2.4
2.2.2.5
2.3
2.3.1
2.3.2
2.3.2.1
2.3.2.2
2.3.2.3
2.3.2.4
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.4.1
2.4.4.2
2.4.4.3
2.4.4.4
2.4.5
2.4.6
2.5
2.5.1
2.5.1.1
2.5.1.2
2.5.1.3
2.5.1.4
2.5.1.5
Moisture content
Ash content
Crude fiber
Fat content
Protein content
Millet composition
Moisture content
Ash content
Crude fiber
Fat content
Protein content
Malting
Grain requirements
Malting technology
Steeping
Germination
Microbial infection
Drying
Amylases
Historical
Sources of amylases
Action
Properties of amylases
Time
Temperature
Activation and inactivation
Influence of pH
Diastatic power development
Mode of action of α amylase
Sorghum and millet malts
Sorghum malt
Modification
Carbohydrates
Carbohydrases
Proteins and proteases
Lipids
12
13
13
13
14
14
14
14
15
15
15
Page
16
17
19
20
21
22
23
24
24
25
26
27
27
28
28
30
30
32
35
37
37
38
39
39
40
2.5.1.6
Minerals
2.5.1.7
Vitamins
2.5.1.8
Microbial aspects
2.5.2
Millet malt
2.5.2.1
Proteolysis
2.6
Application of the falling number system
2.7
Baking properties
CHAPTER THREE: MATERIALS AND METHODS
3.1
Materials
3.1.1
Sorghum and millet grains
3.1.2
Wheat flour
3.1.3
Preparation of sorghum and millet grains for
malting process
3.2
Methods
3.2.1
Proximate analysis
3.2.1.1
3.2.1.2
3.2.1.3
3.2.1.4
3.2.1.5
3.2.1.6
3.2.1.6.1
3.2.1.6.2
3.2.2
3.2.2.1
3.2.2.2
3.2.2.3
3.2.3
3.2.4
3.2.4.1
3.2.4.2
3.2.5
3.2.5.1
3.2.5.2
3.2.5.3
3.2.5.4
3.2.6
3.2.7
40
41
41
42
43
43
44
47
47
47
47
47
47
47
Page
Moisture content
47
Ash content
48
Protein content
49
Fat content
50
Crude fiber
50
Sugar determination
51
Reducing sugars
51
Total sugars
52
Optimization of germination conditions
52
Optimization of temperature, time and salt 52
concentration
Salt concentration
53
PH
53
Preparation of sorghum and millet malt
53
Bread making
54
Preparation of wheat/malt flour for baking
54
Preparation of bread samples
54
Physical analysis
55
Bread volume
55
Bread specific volume
55
Determination of α amylase activity
55
Farinograph
56
Sensory evaluation
58
Statistical analysis
58
CHAPTER FOUR: RESULTS AND DISCUSSIONS
Chemical composition of flour of millet grains
4.1
and malt
4.1.1
Proximate composition
4.1.1.1
59
59
4.1.1.2
4.1.1.3
4.1.1.4
4.1.1.5
4.1.1.6
4.1.2
59
59
60
60
60
60
61
Moisture content
4.1.3
4.1.3.1
4.1.3.2
4.1.3.3
4.1.3.4
4.1.3.5
4.1.3.6
4.1.4
4.2
4.2.1
4.2.2
4.2.3
4.3
4.4
Ash content
Crude fiber
Crude oil
Crude protein
Carbohydrate content
Total and reducing sugars
Proximate composition of flour of sorghum grain
and malt
59
59
Page
Moisture content
61
Ash content
61
Crude fiber
62
Fat content
62
Crude protein
62
Carbohydrate content
63
Total and reducing sugars
63
Effect of interaction time and temperature on 64
falling number of germinated millet and sorghum
(Tabat and Faterita)
Effect of interaction of time-temperature on 64
falling number of millet malt
Effect of interaction of time-temperature on 69
falling number of Tabat malt
Effect of interaction of time-temperature on 69
falling number of feterita malt
Effect of pretreatment of soaking water pH on 77
falling number value of germinated millet and
sorghum)Tabat and Faterita)
The effect of presoaking conditions distilled 80
water, tap water and NaCl solution of 0.5% and
1% in the falling number values of millet and
sorghum (Tabat and Faterita) malt
4.5
4.6
4.7
4.8
Effect of amounts of millet and sorghum (Tabat
and Faterita) malts required to optimize falling
number range (250 – 300) for wheat flour
Effect of addition of millet and sorghum (Tabat
and Faterita) malts on specific volume of wheat
bread
Effect of edition of millet and sorghum (Tabat
and Faterita) malts on specific volume of wheat
breads
81
85
85
Sensory evaluation of breads
88
Conclusion
92
Recommendations
93
REFERENCES
94
List of Tables
Page
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Chemical composition of flours of millet and
sorghum grains and malts
The effect of germination times on falling number
values of millet and sorghum (Tabat and Faterita)
grains
The effect of incubation temperatures on the
falling number values of millet and sorghum
(Tabat and Faterita) grains
The effect of interaction between time and
incubation temperature on the falling number
values of millet grains
The effect of interaction between time and
incubation temperature on the falling number
values of Tabat grains
The effect of interaction between time and
65
66
67
68
74
75
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 13
incubation temperature on the falling number
values of faterita grains
Effect of pH of soaking water on falling number
values of millet and sorghum (Tabat and Faterita)
malts
Effect of soaking conditions distilled water, tap
water and NaCl solutions of 0.5% and 1% on
falling number of germinated milled and sorghum
(Tabat and Faterita)
Dough rheological properties of composite wheat
flour with millet and sorghum (Tabat and Faterita)
malts
Effect of amounts of millet and sorghum (Tabat
and Faterita) malts optimize falling number range
(250-300) for wheat flour
Effect of addition of millet and sorghum (Tabat
and Faterita) malts on specific volume of wheat
bread
Effect of added malt of millet and sorghum on
sensory evaluation of bread (range of scores)
Effect of added malt of millet and sorghum on
sensory evaluation of bread (statistical analysis)
78
82
84
86
87
90
91
List of Figures
Page
Fig. 1
Effect of optimum incubation germination
temperature 30oC and time 72 hrs on the falling
number values for millet and sorghum (Tabat and
faterita)
70
Fig.2
Effect of pretreatment of soaking water pH on
falling number values for millet and sorghum
(Tabat and faterita) malts.
76
Fig. 3
Effect of type of soaking water on falling number
values of different samples
79
Fig. 4
Effect of addition of malt from different sources
to wheat flour on falling number values
83
List of Plates
Page
Plate 1
Malted millet grains as effected by different time
of germination (24, 48 and 72 hrs)
71
Plate 2
Malted millet grains as effected by different time
of germination (24, 48 and 72 hrs)
72
Plate 3
Malted Feterita grains as effected by different
time of germination (24, 48 and 72 hrs)
73
Plate 4
Breads of commercial wheat flour with millet,
Tabat, Feterita malt and control
89
Abstract
This study was carried out to test the
effect of addition of grain malts to wheat flour
on the quality of bread.
The results of chemical composition of millet and sorghum (Tabat and Faterita)
grains before and after germination showed significant increase in protein
content when the grains germinated, significant decrease in fiber content and
insignificant increase in reducing sugars.
Different soaking conditions prior to malting, were examined
including distilled water, tap water, 0.5% and 1% sodium chloride
solutions, and soaking water with variable pH values of 5, 6, 7 and 8.
Germination conditions of different incubation temperatures
(25, 30 and 35oC) and time (24, 48 and 72 hours) were also examined
in order to optimize amylase activity. The falling number test was
used to determine the activity of α-amylase.
Optimization of malting temperature and time were first examined. Results indicated that the incubation
temperature 25oC for millet and sorghum (Tabat and Faterita) grains was reduced significantly the falling number of
germinated grains, as the time progressed from 24 to 48 and 72 hours. Incubation temperature of 35oC for millet and
sorghum (Tabat and Faterita) significantly increase the falling number with time. Incubation temperature of 30oC for millet
resulted in a significant decrease in falling number from the 24 germination time, thereafter it remained unchanged up to 72
hours. Both Tabat and Faterita responded to incubation temperature of 30oC, the falling number significantly reduced from
initial to the first 24 hours. Then it significantly increased with progress of time (24, 48, and 72 hours).
Pre-malting treatment indicated that soaking cereal grains
(millet, Tabat and Faterita) in distilled water gave significant lowering
of falling number for their malts (i.e higher α-amylase activity) if
compared with soaking in NaCl solution of 0.5% and 1%. Despite of
their insignificant variation in falling numbers, soaking grains in
distilled water gave the lowest malt falling number comparable to tap
water. Both pH 7 and 8 gave an insignificant difference in falling
number tests but soaking the grains in pH 7 revealed the lowest malt
falling number in millet and Faterita germinated grains.
The specific volume of bread increased when millet and Faterita
malt were added to wheat flour to 4.506 and 4.306 respectively, while
Tabat malt showed decrease in the specific volume (4.12) comparable
to control sample (4.187). The sensory evaluation of bread samples
showed that the bread baked from composite wheat flour and millet
malt showed best result according to the preference of panelists in
appearance, taste, colour, texture and odour.
‫ﺨﻼﺼﺔ ﺍﻷﻁﺭﻭﺤﺔ‬
‫‪.‬‬
‫ﺃﺠﺭﻴﺕ ﻫﺫﻩ ﺍﻟﺩﺭﺍﺴﺔ ﺒﻐﺭﺽ ﺍﺨﺘﺒﺎﺭ ﺘﺄﺜﻴﺭ ﺇﻀﺎﻓﺔ ﺍﻟﺯﺭﻴﻌﺔ ﺇﻟﻰ ﺩﻗﻴﻕ ﺍﻟﻘﻤﺢ ﻭﺃﺜﺭ‬
‫ﺫﻟﻙ ﻋﻠﻲ ﻨﻭﻋﻴﺔ ﺍﻟﺨﺒﺯ ﺍﻟﻤﺼﻨﻊ‪.‬‬
‫ﺃﻅﻬﺭﺕ ﻨﺘﺎﺌﺞ ﺍﻟﺘﺤﻠﻴل ﺍﻟﻜﻴﻤﺎﺌﻲ ﻟﻜل ﻤﻥ ﺍﻟﺩﺨﻥ ﻭﻋﻴﻨﺎﺕ ﺍﻟﺫﺭﺓ )ﻁﺎﺒﺕ ﻭﻓﺘﺭﻴﺘﻪ( ﻗﺒل‬
‫ﻭﺒﻌﺩ ﺍﻟﺘﺯﺭﻴﻊ ﻋﻥ ﻭﺠﻭﺩ ﺯﻴﺎﺩﺓ ﻤﻌﻨﻭﻴﺔ ﻓﻲ ﺍﻟﻤﺤﺘﻭﻱ ﺍﻟﺒﺭﻭﺘﻴﻨﻲ ﻭﻨﻘﺼﺎﻥ ﻤﻌﻨﻭﻱ ﻓﻲ ﻤﺤﺘﻭﻱ‬
‫ﺍﻷﻟﻴﺎﻑ ﺇﻀﺎﻓﺔ ﺇﻟﻰ ﺯﻴﺎﺩﺓ ﻏﻴﺭ ﻤﻌﻨﻭﻴﺔ ﻓﻲ ﺍﻟﺴﻜﺭﻴﺎﺕ ﺍﻟﻤﺨﺘﺯﻟﺔ‪.‬‬
‫اﺧﺘﺒﺮت ﻇﺮوف اﻟﻐﻤﺮ اﻟﻤﺨﺘﻠﻔﺔ اﻟﺴﺎﺑﻘﺔ ﻟﻌﻤﻠﻴﺔ اﻟﺘﺰرﻳﻊ ﺑﺤﻴﺚ ﺗﻢ اﺱﺘﺨﺪام آﻞ ﻡﻦ ﻡﺎء اﻟﺼﻨﺒﻮر‬
‫ﺑﺎﻹﺿﺎﻓﺔ إﻟﻰ ذﻟﻚ ﻡﺎء ﻏﻤﺮ ذو )‪(0.5-1%‬واﻟﻤﺎء اﻟﻤﻘﻄﺮ وﻡﺤﺎﻟﻴﻞ آﻠﻮرﻳﺪ اﻟﺼﻮدﻳﻮم ﺑﺎﻟﺘﺮاآﻴﺰ اﻟﻤﺨﺘﻠﻔﺔ‬
‫)‪(5, 6, 7, 8‬درﺟﺎت أس هﻴﺪروﺟﻴﻨﻲ ﻡﺨﺘﻠﻔﺔ‬
‫ﺃﻴﻀﺎ ﺍﺨﺘﺒﺭﺕ ﻅﺭﻭﻑ ﺘﺯﺭﻴﻊ ﻤﺘﻔﺎﻭﺘﺔ ﻟﺩﺭﺠﺔ ﺤﺭﺍﺭﺓ ﺘﺤﻀﻴﻥ )‪(25, 30, 35oC‬‬
‫ﻭﺯﻤﻥ )‪ (24, 48, 72 h‬ﻤﺨﺘﻠﻔﺔ ﺒﻐﺭﺽ ﺍﻟﻭﺼﻭل ﻟﺩﺭﺠﺔ ﻨﺸﺎﻁ ﻤﺜﻠﻲ ﻻﻨﺯﻴﻡ ﺍﻻﻟﻔﺎ ﺍﻤﻴﻠﻴﺯ‪.‬‬
‫ﺃﺴﺘﺨﺩﻡ ﺍﺨﺘﺒﺎﺭ ﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ﻟﺘﻘﺩﻴﺭ ﻨﺸﺎﻁ ﺍﻻﻟﻔﺎ ﺍﻤﻴﻠﻴﺯ‪.‬‬
‫ﺃﻭﻻ ﺘﻡ ﺍﺨﺘﺒﺎﺭ ﻜل ﻤﻥ ﻋﺎﻤﻠﻲ ﺩﺭﺠﺔ ﺍﻟﺤﺭﺍﺭﺓ ﻭﺍﻟﺯﻤﻥ‪ .‬ﺩﻟﺕ ﺍﻟﻨﺘﺎﺌﺞ ﺍﻥ ﺩﺭﺠﺔ ﺤﺭﺍﺭﺓ‬
‫‪ ٢٥‬ﻟﻜل ﻤﻥ ﺤﺒﻭﺏ ﺍﻟﺩﺨﻥ ﻭﻋﻴﻨﺎﺕ ﺍﻟﺫﺭﺓ )ﻁﺎﺒﺕ ﻭﻓﺘﺭﻴﺘﺔ( ﻗﺩ ﺃﺩﺕ ﺍﻟﻲ ‪oC‬ﺍﻟﺘﺤﻀﻴﻥ ﻓﻲ‬
‫ﺍﻨﺨﻔﺎﺽ ﻤﻌﻨﻭﻱ ﻓﻲ ﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ﻟﻠﺤﺒﻭﺏ ﺍﻟﻤﺯﺭﻋﺔ ﻭﺫﻟﻙ ﺒﺘﻘﺩﻡ ﻋﺎﻤل ﺍﻟﺯﻤﻥ ﻤﻥ ‪،٤٨ ،٢٤‬‬
‫‪ ٣٥‬ﻟﻠﺩﺨﻥ ﺃﺩﺕ ﺍﻟﻲ ﺯﻴﺎﺩﺓ ﻤﻌﻨﻭﻴﺔ ﻓﻲ ﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ‪ ٧٢oC‬ﺴﺎﻋﺔ‪ .‬ﺩﺭﺠﺔ ﺍﻟﺘﺤﻀﻴﻥ ﻓﻲ‬
‫ﺍﺒﺘﺩﺍﺀ ﻤﻥ ‪ ٢٤‬ﺴﺎﻋﺔ ﺍﻷﻭﻟﻰ ﻤﻥ ﻋﻤﻠﻴﺔ ﺍﻟﺘﺯﺭﻴﻊ‪ ،‬ﻟﻴﻅل ﺒﻌﺩﻫﺎ ﺜﺎﺒﺘﺎ ﺤﺘﻰ ﻓﺘﺭﺓ ‪ ٧٢‬ﺴﺎﻋﺔ‪.‬‬
‫‪ ٣٠‬ﺃﺩﺕ ﺇﻟﻰ ﻨﺘﺎﺌﺞ ﻤﺘﺸﺎﺒﻬﺔ ﻟﻜل ﻤﻥ ﻁﺎﺒﺕ ﻭﻓﺘﺭﻴﺘﺔ‪ ،‬ﺒﺤﻴﺙ ‪oC‬ﺩﺭﺠﺔ ﺤﺭﺍﺭﺓ ﺍﻟﺘﺤﻀﻴﻥ‬
‫ﺍﻨﺨﻔﺽ ﻤﻌﻨﻭﻴﺎ ﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ﻤﻥ ﻗﻴﻤﺘﻪ ﺍﻷﻭﻟﻴﺔ ﻋﻨﺩ ‪ ٢٤‬ﺴﺎﻋﺔ ﺍﻷﻭﻟﻲ ﻤﻥ ﻋﻤﻠﻴﺔ ﺍﻟﺘﺯﺭﻴﻊ‬
‫ﻭﺍﻟﺫﻱ ﺒﺩﺃ ﺒﻌﺩﻫﺎ ﻓﻲ ﺍﻟﺯﻴﺎﺩﺓ ﺍﻟﻤﻌﻨﻭﻴﺔ ﺒﺘﻘﺩﻡ ﻓﺘﺭﺓ ﺍﻟﺘﺯﺭﻴﻊ ﺤﺘﻲ ‪ ٧٢‬ﺴﺎﻋﺔ‪.‬‬
‫ﺩﻟﺕ ﻤﻌﺎﻤﻼﺕ ﻤﺎ ﻗﺒل ﺍﻟﺘﺯﺭﻴﻊ ﺍﻥ ﻏﻤﺭ ﺤﺒﻭﺏ ﻜل ﻤﻥ ﺍﻟﺩﺨﻥ ﻭﺍﻟﺫﺭﺓ )ﻁﺎﺒﺕ ﻭﻓﺘﺭﻴﺘﺔ(‬
‫ﻓﻲ ﺍﻟﻤﺎﺀ ﺍﻟﻤﻘﻁﺭ ﺃﺩﻯ ﺇﻟﻰ ﻨﻘﺼﺎﻥ ﻤﻌﻨﻭﻱ ﻓﻲ ﺭﻗﻡ ﺴﻘﻭﻁ ﺍﻟﺯﺭﻴﻌﺔ )ﻴﻌﻨﻲ ﺫﻟﻙ ﺯﻴﺎﺩﺓ ﻓﻲ‬
‫‪0.5‬ﻨﺸﺎﻁ ﺃﻨﺯﻴﻡ ﺍﻻﻟﻔﺎ ﺍﻤﻴﻠﻴﺯ( ﻤﻘﺎﺭﻨﺔ ﺒﺎﻟﻐﻤﺭ ﻓﻲ ﻤﺤﺎﻟﻴل ﻜﻠﻭﺭﻴﺩ ﺍﻟﺼﻭﺩﻴﻭﻡ ﺫﻭ ﺍﻟﺘﺭﺍﻜﻴﺯ )‬
‫ﻭ‪ (%١‬ﺒﺎﻟﺭﻏﻡ ﻤﻥ ﻋﺩﻡ ﻭﺠﻭﺩ ﻓﺭﻭﻗﺎﺕ ﻤﻌﻨﻭﻴﺔ ﻓﻲ ﺃﺭﻗﺎﻡ ﺍﻟﺴﻘﻭﻁ‪ .‬ﻭﺠﺩ ﺃﻥ ﻏﻤﺭ ﺍﻟﺤﺒﻭﺏ‬
‫ﻓﻲ ﺍﻟﻤﺎﺀ ﺍﻟﻤﻘﻁﺭ ﺃﺩﻯ ﺇﻟﻰ ﺍﻗل ﻗﻴﻤﺔ ﻟﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ﻤﻘﺎﺭﻨﺔ ﺒﺫﻟﻙ ﻓﻲ ﻤﺎﺀ ﺍﻟﺼﻨﺒﻭﺭ‪ .‬ﻜل ﻤﻥ‬
‫ﺩﺭﺠﺔ ﺍﻷﺱ ﺍﻟﻬﻴﺩﺭﻭﺠﻴﻨﻲ ‪ ٧‬ﻭ‪ ٨‬ﺃﺩﻯ ﺇﻟﻰ ﻓﺭﻕ ﻏﻴﺭ ﻤﻌﻨﻭﻱ ﻓﻲ ﺍﺨﺘﺒﺎﺭﺍﺕ ﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ‬
‫ﻭﻟﻜﻥ ﻏﻤﺭ ﺍﻟﺤﺒﻭﺏ ﻓﻲ ﻤﺎﺀ ﺫﻭ ﺩﺭﺠﺔ ﺍﺱ ﻫﻴﺩﺭﻭﺠﻴﻨﻲ ‪ ٧‬ﺍﻅﻬﺭ ﺍﻗل ﻗﻴﻤﺔ ﻟﺭﻗﻡ ﺍﻟﺴﻘﻭﻁ ﻟﻜل‬
‫ﻤﻥ ﺍﻟﺤﺒﻭﺏ ﺍﻟﻤﺯﺭﻋﺔ ﻟﻜل ﻤﻥ ﺍﻟﺩﺨﻥ ﻭﺍﻟﻔﺘﺭﻴﺘﺔ‪.‬‬
‫ﺯﺍﺩ ﺍﻟﺤﺠﻡ ﺍﻟﻨﻭﻋﻲ ﻟﻠﺨﺒﺯ ﻨﺘﻴﺠﺔ ﻹﻀﺎﻓﺔ ﻜل ﻤﻥ ﺯﺭﻴﻌﺔ ﺍﻟﺩﺨﻥ ﻭﺍﻟﻔﺘﺭﻴﺘﺔ ﺇﻟﻰ ﺩﻗﻴﻕ‬
‫ﺒﺎﻟﺘﺘﺎﻟﻲ ﺒﻴﻨﻤﺎ ﺃﻅﻬﺭﺕ ﺯﺭﻴﻌﺔ ﻁﺎﺒﺕ ﻨﻘﺼﺎﻥ ﻓﻲ ﺭﻗﻡ )‪4.506 ،((4.306‬ﺍﻟﻘﻤﺢ ﻟﻘﻴﻡ )‬
‫‪ (4.187).‬ﻤﻘﺎﺭﻨﺔ ﺒﻌﻴﻨﺔ ﺍﻟﺸﺎﻫﺩ )‪(4.120‬ﺍﻟﺴﻘﻭﻁ‬
‫ﺍﻟﺘﻘﻴﻴﻡ ﺍﻟﺤﺴﻲ ﻟﻌﻴﻨﺎﺕ ﺍﻟﺨﺒﺯ ﺃﻅﻬﺭﺕ ﺃﻥ ﺍﻟﺨﺒﺯ ﺍﻟﻤﺼﻨﻊ ﻤﻥ ﻤﺨﻠﻭﻁ ﺩﻗﻴﻕ ﺍﻟﻘﻤﺢ‬
‫ﻭﺯﺭﻴﻌﺔ ﺍﻟﺩﺨﻥ ﻗﺩ ﺃﻋﻁﻰ ﺍﻟﻔﻀل ﺍﻟﻨﺘﺎﺌﺞ ﺍﺴﺘﻨﺎﺩﺍ ﺇﻟﻰ ﺘﻘﻴﻴﻡ ﺍﻟﻤﺤﻜﻤﻴﻥ ﻻﺨﺘﺒﺎﺭﻫﻡ ﻟﻠﻤﻅﻬﺭ‪،‬‬
‫ﺍﻟﻁﻌﻡ‪ ،‬ﺍﻟﻠﻭﻥ‪ ،‬ﺍﻟﻘﻭﺍﻡ ﻭﺍﻟﺭﺍﺌﺤﺔ‪.‬‬
CHAPTER ONE
INTRODUCTION
Enzymes were active in baked goods long
before bakers fully understood the mechanism
of reactions taking place. It has long been
known, for example that certain flours
produce stickier dough, but it has not always
been clear whey this occurs. We know now
that enzymes greatly affect flour and thus
dough properties, such as stickness, gassing
and final crumb texture.
Wheat flour naturally contains α and β-amylases, which
hydrolyze glycosidic linkages in carbohydrates. The amount of these
enzymes depend on the wheat’s growing and harvesting conditions,
for example the α-amylase content of flour increases in wet climates
because this enzyme mobilizes reserved startch during germination.
Alpha amylase hydrolyzes starch into dextrins, which may
subsequently be hydrolyzed by β-amylase into maltose or by
amyloglucosidase into glucose. However, the tightly packed starch
granules must first be made accessible, either by damage during flour
milling or gelatinization by heat and moisture. The amylase
hydrolyzed sugars are then used by yeast during the baking process.
The proper amount of amylases must be present in flour to achieve the
right amount of yeast fuel and thus resulting in suitable carbon dioxide
generation (gassing level).
Amylases also can help prevent staling of baked goods by
affecting starch retrogradation (recrystallization). Bacterial amylase is
best for this purpose because it can continue working after baking is
completed.
The Sudanese wheat varieties, however, are characterized by
abnormally high FN, which indicates low α-amylase activity.
Provision of suitable amounts of α-amylase by cereal grains,
furnishing fermentable sugars for yeast; thus produces breads with
acceptable quality. Therefore the baker can rectify insufficient alpha
amylase activity in flour by adding a little malt flour, malt extract or
fungal amylase in dough making.
Objectives:
1.
Optimization of the germination conditions, which
include time, temperature type of soaking water and
soaking water pH.
2.
Determination of the alpha-amylase activity using falling
number as index.
3.
Effect of malt on bread baking quality.
CHAPTER TWO
LITERTURE REVIEW
2.1 Wheat composition
Wheat ranks first among cultivated plants of the world and provides
more nourishment to the people than any other food source and contributes
substantially to the feeding of the domestic animals. Although the major
pressure to increase world wheat production comes from food sector.
Potential industrial uses of the wheat are also well known and in times of
world, surpluses. There is considerable disscussion of wheat becoming an
important renewable resource of raw materials for chemical
industries.Wheat in Sudan is grown under irrigation during the dry and
comparatively cool winter season which extends from November to
February. With the present commerical varieties potentioal yield is limited
by day temperature above 35oC at any stage for crop development. Wheat is
considered as one of the two main food crops in Sudan ,it ranks after
sorghum as astaple diet especially in urban centers.The increasing
importance of wheat is reflected from its increased consumption which
increased from 419,000M tons to 920,000 M tons during the period 1980-1992
(Mohamed,1992).In addition to its use as bread, wheat enterd into other uses
and encouraged the growth and development of many industries such as
biscuits, cakes, macaroni, and others.
Composition of the grain makes it a
palatable food of high-energy value, which
leads the nutritionist to have a major interest
in the composition of the kernel.
Botonically the wheat grain consists of a fibrous outer layer
(bran), starchy endosperm (flour) and embryo (germ) as reported by
Bushuk, (1986). The endosperm constitutes about 83% of the kernel
weight and it is the source of the wheat flour and contains the greatest
share of protein in the whole kernel. The bran constitutes about 14.5%
of kernel weight while the germ constitutes 2.5% of the kernal. The
bran contains a small amount of protein, an appreciable amount of Bcomplex vitamins . The wheat bran contains minimal quantities of
protein, but greater B-complex vitamins and trace minerals and very
rich in oil content (Anon, 1978). The composition of wheat flour
varies considerably according to the class of wheat, it's origin and the
proportion of outer part removed by particular milling process.
2.1.1 Moisture content
Moisture content has a direct economic importance wheat
generally contains 14% moisture resulting in an ambient relative
humidity suitable for the growth of insects and other microorganism
whose presence will markedly reduce the grain quality (Williams,
1970; Zeleny 1971).
Pareds-Lopez et al., 1978) reported that the moisture content
of Mexican wheat flour is 11.2% however, Badi et al., (1976) found
that the moisture content of Sudanese wheat flour, where grains were
harvest in 1975, ranges between 10 - 11%.
2.1.2 Ash content
Ash content of wheat is directly related to the amount of bran
in the wheat, and hence has a rough inverse relationship to flour yield.
The ash content of the wheat flour was found to be in the range of
0.2% to 0.5% (Zeleny, 1971). D'appolonia and Young (1987) reported
that ash content of wheat flour is 0.53% while Pareds-Lopez et al.,
(1978) reported that ash content of wheat flour (69% extraction)
ranges between 0.31 - 0.62%.
Egan et al. (1981) reported that ash content of wheat flour
ranges between 0.2 - 0.8%. Badi et al., (1976) reported that ash
content of Sudanese wheat flour ranges between 0.38 - 0.84%.
2.1.3 Protein content
George (1973) reported that protein content of the wheat is
highly affected by environmental conditions, grain yield and available
nitrogen as well as the variety genotype. The percentage of wheat
protein may be considered as a criterion for establishing the economic
value of grain and will be useful (William's, 1970). Haldor et al.,
(1982) reported that protein content of whole wheat flour ranges
between (10 - 16%) while Passmer and Eastwood (1986) reported that
protein content of wheat was 12.2 gm/100 gm. Ahmed (1995) reported
that the protein content of four Sudanese wheat cultivars (Condor,
Deberia, Elneilein and Nasser) ranges between 8.21 and 12.26%.
2.1.4 Fat content
The fat content of four Sudanese wheat flour (100%
extraction) and (72% extraction rates) of different cultivars grown in
seasons 1991/92 ranged between 1.91 - 2.35% and 0.85 to 1.73%
respectively (Ahmed, 1995). Mohamed, (2000) reported that the fat
content of four Sudanese cultivars (Debera, Elneilian, Condor and
Sasaraib) ranges between 2.15 and 2.35%.
2.1.5 Fiber content
Crude fiber consists largely of the cellulose content together
with a proportion of the lignin and hemicellulose content of the
sample (Egan, et al., 1981). Ahmed (1995) reported that crude fiber
content of four Sudanese wheat cultivars (Condor, Debera, Elneilein
and Nasser) ranges between 1.75 and 2.34%. Mohamed (2000)
reported that the crude fiber content of four Sudanese wheat cultivars
(Sasaraib, Condor,
Elneilain and Debira) ranged between 2.10% and 2.85%.
2.1.6 Starch
Chemically, starch is a high molecular weight polymer of Dglucose and is the principal reserve of carbohydrate in plants (Pazur
1965). Mayer (1942) pictured the normal starches as composed of two
polymeric carbohydrates, a linear chain of 400 - 1000 glucose units
(the A-fraction or amylose) and branched or tree like molecule of
several thousands glucose units (the B-fraction or amylopectin). In the
linear polymer of starch (amylose or A-fraction), the glucose units are
joined by α-D (1 - 4) linkage (Pazur 1965).
The types of linkages that have been definitely established in
amylopectine molecule are the α-D (1-4) and α-D (1-6) the latter
linkage gives rise to the so-called branch points in the molecule.
Amylopectin is one of the largest polysaccharides known with a
molecular weight of 10 - 500 X 106 (Brand, 1988).
Starch is digested in the human by α-amylase which
hydrolyses α-D (1-4) glucasidic bonds, in two reactions. Initially it
breakdown starch to maltose, some maltotriose and a little glucose.
Overtime it hydrolyze maltotriose to maltose and glucose (Walker and
Whelam 1960).
2.1.6.1 Variation in starch molecules for different crops
Amylose and amylopectin are the major molecular constituents
of starch (Jane et al., 1992). Proportion of each depend on starch
sources (Lineback 1984). The ratio of amylose to amylopectin in any
starch is under genetic control, however, with wheat variations in the
ratio appears to be small (Hoseney et al. 1978). In non waxy sorghum
both environment and genetic factors effect on the level of amylose
content have not been clearly demonstrated (Ring et al., 1981).
Amylopectin is the main structural component of starch granule while
amylose contributes to the internal strength. The two molecules are
arranged in a radial direction and link together into a submicroscopic
paracrystalline pattern by hydrogen bond (Richard, 1969). According
to Badi (1973) the sorghum starch contained 23% amylose and millet
starch 17% amylose, while the amylopectin content was 77% and 83%
respectively. Normal corn starch contains about 28% amylose and
72% amylopectin, the relative proportion of amylose and amylopectin
influence the physical properties and behaviour of starches (Hulse et
al., 1980). Starches susceptibility to digestion is also influenced by the
amylose to amylopectin ratio (Srinivasa, 1976).
2.1.6.2 Gelatinization of starch
The subjection of aqueous suspension of starch to the
influence of heat or appropriate chemicals. According to Leach (1965)
weakens the molecular network within the granule by disrupting
hydrogen bonds, this permits further hydration and irreversible
granule swelling, this process is termed gelatinization. Seib (1971)
defined gelatinization as an irreversible rupture of native secondary
bond force in the crystalling regions of starch granules, Darrel (1973)
attributed the swelling properties of starch to the contribution and
interaction of three major starch characteristics. This is due to its
highly hydroxylated nature due to the D-glucose molecules, the large
molecular size of the constituent polymers and the granular form
itself. According to Leach (1965), the swelling behaviour of starch
depends primarily on the strength and character of the micellar
network within the granule. This, in turn depends on the ratio of
amylose and amylopectin, the size of the molecules, their degree of
original
association
and
the
presence
of
non
carbohydrate
components. Leach (1965) stated that three different criteria have been
used to detect gelatinization temperature: loss of birefringence
increase in optical transmitancy and rise in viscosity. Measurement of
the loss of birefringence is the most sensitive accurate and
reproducible technique for detecting the initial gelatinization of starch.
Gelatinization patterns vary with the source of starch (Leach, et al.
1959). Badi (1973) using kofler hot stage microscope showed that
sorghum and
millet
starches
(1%
suspension)
gelatinization
temperature ranged from 63oC to 74oC and 51oC to 69oC respectively.
2.1.6.3 Non carbohydrate constituents of starch
According to Leach (1965) most starches when equilibrated
under normal atmospheric conditions contain 10 - 17% moisture, the
efficiency of starch isolation depends on the success of separating
individual starch granules from the proteinaceous matrices in which
they are produced (Rezsoe, 1965).
Norris and Rooney (1970) reported that the protein content of
sorghum starch at the extent of 0.8 to 1.9%. Beleia et al. (1980) found
that protein content in millet starches is higher than most cereal
starches, the protein content of commercial corn starch was 0.29%
(Hoseney et al. 1974). Badi and Monawar (1987) found 0.36% and
0.12% fat content in sorghum and corn starches respectively.
2.1.6.4 Hydrolysis of wheat starch and its effect on the falling
number procedure:
Starch is the major source of carbohydrates in the human diet.
Synthesized within the storage organs (amyloplasts) of the cereals,
such as wheat, starch molecules form tiny (around 10 micrometers)
white granules that are insoluble in cold water. Within the molecule,
starch consists of hundreds of glucose units, which by enzymatic
hydrolysis are cleaved in the presence of heat and hydration. In
addition to extensive study at the molecular level, starch hydrolysis
has been widely examined at the macro level through the rheological
changes that occur to a heated starch water solution as granules swell
and rupture. However, scant information exists on mathematical
modeling to describe the competing kinetic events of gelatinization,
hydrolysis and enzyme (alpha amylase) activity. The a current
research was directed toward developing such a model, there using
this to describe the bahaviour of a viscometer-type instrument (i.e.,
falling number) used worldwide to measure the starch - related
processing characteristics of wheat and barely. Through modeling of
starch hydrolysis, grain-testing apparatus can be better utilized to
ascertain the subtle but significant cooking properties of cereals.
Moreover, traders and processors will gain an enhanced understanding
of the processing characteristics of grain lots during scale-up
operations.
Associated with certain climatic conditions, mature wheat
kernels while still in the filed may begin to break dormancy. During
this condition of pre-harvest sprouting, endosperm starch macro-
molecules are broken down through the increased action of the
enzyme, alpha amylase. Flour, which is produced from affected
wheat, is of poor quality. A simple screening procedure known as the
falling number (FA) test, is used to gauge the level of alpha amylase
activity. It is an empirical method, which reports the time needed for a
rod of specific geometry to fall through a heated flour/water (i.e. gel)
solution. It is based on the inverse relationship between the viscosity
of a heated gel (related to falling time) and the level of gel's alphaamylase activity. Experimental data showed that the variability of FN
readings can be reduced by slowing the heating rate. (Chang S.Y. et
al, 1997).
2.2 Sorghum and millet
Cereals are the major source of energy for most people of the
world. They provide from 45 - 56% of the calories of the American
diet and used at a higher percent for many other people (Mitchell et
al., 1976).
Grain sorghum [sorghum bicolor (L.) Moench] is commonly
consumed by the poor masses of many countries. It forms a major
source of protein and calories in the diets of large segments of
population of India and Africa. The poor nutritional quality of grain
sorghum has been attributed to the low level of certain essential amino
acids especially lysine, thorenine and triptophan, excessive content of
lysine, type and texture of starch (Taur et al., 1984).
Badi and Hoseney (1977) found that millet has higher values
of lysine, arginine, aspartic acid and low values of glutamic acid,
proline, alanine and leucine than sorghum grains. Other important
factors affecting the nutritional value of sorghum are the presence of
free and condensed polyphenolic compounds, such as proanthocyanidines and tannins (Eggum et al. 1983).
2.2.1 Sorghum composition
2.2.1.1 Moisture content
Yousif and Magboul (1972) whom analyzed fifteen sorghum varieties grown in the Sudan reported that
moisture content ranges between 5.7% and 10% ,while Arbab (1995) analyzed two Sudanese sorghum cultivars
(Gadam Elhamam and Keramaka) showed that the moisture content ranged between 8.89% and 9.88%.
2.2.1.2 Ash content
Hassan (1994) reported that the ash content of two-sorghum
cultivars safra and cross 35:18 was 1.52% and 3.95% respectively.
Yousif and Magboul (1972) determined the ash content of different
cultivars of dura (sorghum) grown in different parts of Sudan it ranged
from 1.2% to 2.6%.
2.2.1.3 Crude fiber
Shepherd et al. (1970) reported that crude fiber content is
1.3%, while Bredon (1961) reported 3%.
Eltinay et al. (1979)
reported that, crude fiber content of three sorghum cultivars ranged
from 1.2% to 1.9% while Abdelrahman (2000) reported that the crude
fiber ranged from 1.4% to 2% for two sorghum cultivars (fetarita and
ahmer).
2.2.1.4 Fat content
Rooney and Miller (1981) reported that the fat content of
sorghum was 3.4% whereas Shepherd et al. (1970) reported that crude
fat content of sorghum cultivars ranged from 2.5% to 1.5%. Khattab et
al., (1972) reported that crude fat of three sorghum cultivars faterita,
safra and ahmer ranged from 2.7 to 3.0%.
2.2.1.5 Protein content
Abdelrahman (2000) reported that the protein content of three
sorghum cultivars safra, faterita and ahmer was 10.1% 13.6% and
11.1% respectively. Eggum et al. (1983) reported that the protein
content of three sorghum cultivars tetron, deber and faterita was 10.9,
11.6 and 13.4 respectively, while Eltinay et al. (1979) reported that
the protein content of sorghum grains ranged from 9.76% to 11.6%.
2.2.2 Millet composition
2.2.2.1 Moisture content:
According to Ahmed (1999) the moisture content of two pearl
millet cultivars was 8.2% and 7.6%. Badi et al. (1976) and Opoku et
al. (1981) gave the range of 10 to 10.6% for moisture content of pearl
millet. Johnson and Raymond (1964) reported that the moisture
content of whole grain as 11.9 and 12.0% while Ali (2001) reported
that the moisture content of two Sudanese pearl millet cultivars ranged
from 7.3% to 7.5% respectively.
2.2.2.2 Ash content
According to Burton et al. (1972) the ash content of pearl
millet ranged from 1.46% to 3.88%. Basahy (1996) found that 2.4%
ash content of pearl millet, while Hadimani et al. (1995) found a range
of 1.2% to 2.4%. Ali reported that the ash content of two Sudanese
cultivars of pearl millet ranged from 2.1% to 2.4%.
2.2.2.3 Crude fiber
Khatir (1990) reported that the fiber content for Sudanese local cultivars
ranged from 3.2% to 3.7%, while Ahmed (1999) reported that the fiber content is
in the range of 3.8% to 4.1%. Elyas (1999) reported 2.0% and 2.3% fiber content
for two pearl millet cultivars.
2.2.2.4 Fat content
The fat content of pearl millet was considered to be higher
than other cereals. The high content of oil is due to the large
proportion of the germ to the endosperm, most lipids concentrated in
the germs, pericarp and a leurone layer (Rooney 1978; Lai and
Varriano-Marston 1980). Saxena et al (1992) reported that the fat
values of pearl millet ranging between 4.08% and 6.37%. Abdalla
(1996) reported that the oil content ranged from 2.7% to 7.1% while
Elyas (1999) found that 6.2% and 8.5% oil content for two pearl millet
cultivars.
2.2.2.5 Protein content
Generally pearl millet has a higher protein content than other
cereals grown under similar conditions. Singh et al. (1987) showed
that the protein content of high protein genotypes ranged from11.3%
to 20.8% while local Sudanese cultivars proteins ranged from 14.2%
to 15.5% which was higher than sorghum, maize and rice as reported
by Khatir (1990).
2.3 Malting
Malting is a process where the grains are allowed to germinate
under controlled conditions of temperature and moisture (Adsule et
al., 1984). Both genetic and environmental factors have been reported
to influence the grain and malting quality of sorghum (Daiber and
Achting, 1970).
In Sudan for all practical purposes, all sorghum malt (zurria) is
prepared from sorghum variety (faterita) and only a little amount of
malt is prepared from millets such as pearl millet and finger millet.
Sorghum malt is prepared and used throughout the country, while
millet malt is confined to certain localities, the duration of the
germination stages of the grain depends largely on the environmental
conditions and the integrated use of the final malt, sorghum grain malt
is used after grinding to fine or coarse flour.
Malts made from grain sorghum have primarily been used for
the brewing of opaque beer and have received most attention in
research. Sorghum suitable for milling must meet more stringent and
specific requirements than sorghum used for feed, food or adjunct.
2.3.1 Grain requirements
The grain must be viable, that is to germinate under favorable
conditions rapidly, within 48 hr to at least 92 - 95% and be free of
parasitic fungi and bacteria. Growth, harvest and storage conditions of
the grain require special precautions to maintain and improve viability
and hygiene of the grain. Inherent or genetic properties of sorghum
have been found to play a critical role in the suitability of sorghum for
malting and brewing (Novellie 1962b, Daibar 1978; Jayatissa et al.,
1980).
The malt of the bird-resistant group of cultivars has been
found to be unsuitable for brewing. Responsible for that are the tannis
or condensed polyphenols deposited under genetic control in varying
concentrations in the peripheral tissue of the testa (Rooney et al.,
1980).
The enzymes produced during malting are complexes in the
aqueous solution of the mash to become insoluble and inactive. Only
when the causative tannins are neutralized in the intact grain prior to
malting (Daiber, 1975) are malts of these cultivars suitable for
brewing.
In harvest grain properties also determine the enzyme
concentration, the extract, the composition of soluble solids in the
malt and they determine the susceptibility of grain to microbial
infection, it is thus essential to select and market the consistently most
suitable sorghum cultivar for successful malting.
Efforts over the last decade (Daiber, 1988) have defined
objective selection procedures, identified components of malting
quality, and guided sorghum breeders to improve the malting quality
of new agronomically better sorghum hybrids by active, selective,
breeding. In South Africa and Zimbabwe (House, 1988), identification
and marketing of sorghum cultivars, suitable for malting are actively
pursued.
These efforts correspond to those for the improvement of
barley for malting. They must continue to meet better-defined
requirements for agronomic performance and for brewing opaque
beer, but also those for additional specifications for brewing clear,
hopped beers with sorghum malts to replace expensive imported
barley malt.
Sorghum malting quality is also affected by conditions during
growth production, and storage of the crop. Soil fertility, particularly
available nitrogen, improves the protein content of the grain, enzyme
content and soluble amino nitrogen in the malt (Daiber, 1978). All
measures and conditions, such as late and narrow planting and drought
conditions, which tend to increase the proportion of the embryo,
improve enzyme formation and concentration as well as the content of
free amino nitrogen (FAN) but decrease yield of grain and extract of
malt.
Harvest and storage conditions are crucial for the preservation
of sorghum viability and hygiene. Sorghum for malting must be
harvested at full ripeness, at low grain moisture, with particular care to
prevent breaking or racking the grain by threshing. Prior to storage,
grain must be dried to a safe moisture level of below 12% moisture,
either pneumatically at temperatures below 50oC with high air
circulation or in thin layers with frequent turning. Dust, loose husks,
broken grain and foreign substances must be removed. Size selection
by sieving should retain small sound grains, which produce high
diastatic activity, although lower extract than larger-sized grain.
Extract in opaque beer brewing is, however, more economically
supplied by unmalted cereals used as adjunct. The cleaned sorghum
must be stored protected against storage insects. If insecticides must
be used, they must be free of residue and not reduce the viability of
the seed.
2.3.2 Malting technology
The malting process of sorghum in principle is similar to that
of barley initiated by steeping (soaking) the grain to hydrate the
embryo for active growth and germination. The germinating grain is
subsequently maintained at optimal levels of moisture, temperature,
and aeration to support the endosperm at a rate to keep respiration
losses to the minimum necessary to achieve the quality of malt for
enzymes during storage (Novellie, 1962a, Rathirana et al., 1983).
2.3.2.1 Steeping
The uptake of water during steeping is controlled by physical
absorption and diffusion to about 35% (wet basis) moisture.
Further hydration is dependent on the metabolic activity of the
germinating embryo. Inhibition of metabolism by temperature below
15oC, by high CO2 concentration and other, restricts water absorption
to below the level of about 37% moisture essential for germination.
Steeping after the physical absorption phase of about 6 to 8 hr requires
temperatures above 18oC and sufficient aeration of the steep water or
periods of air rest adjusted to the physiological requirements of the
germinating sorghum (Hofmyer, 1970).
The application of gibberellic acid during or at the end of
steeping has failed to trigger enzyme synthesis in the embryo or
aleurone (Daiber and Novellie, 1968; Aisien et al., 1983: Mundy et
al., 1963) as in the case of barley. To prevent the subsequent
inhibitory effects of tannins during brewing, bird resistant sorghum is
steeped in a dilute (0.04-0.08% w/w) formaldehyde solution for the
first 4 hrs of steeping. The formaldehyde diffusing radially into the
grain complexes the inhibiting polyphenol deposited in the outer,
peripheral layer of such sorghum (Daiber, 1975). The fungicidal
properties of the formaldehyde cause, in addition, a degree of surface
sterilization, although subcutaneous infection is not or incompletely
controlled. The phytotoxic formaldehyde must be precisely dispensed,
drained and raised after 4 hrs.
2.3.2.2 Germination
The steeped grain is cast onto a suitable support. This can be
open or covered, slightly sloping floor for beds of up to 0.3 m depth.
For beds of up to 1.5 m depth it must be perforated floor on top of a
ventilation duct. On the floor the steeped grain is maintained at
optimum temperature, moisture, and aeration for the desired rate of
germination. Morrall et al. (1986) obtained the highest malt quality
attributes, namely, diastatic power, FAN and extract at malt
temperatures of 24oC, slightly, but not significantly, better than results
at 28oC.
Malting performed under frequent watering reached maximum
quality after 4.5 to 5.5 days on the floor. Higher malting temperatures
and lower moisture of the malt reduced all quality attributes
significantly. Previously, Novellie (1962a) had similar results for
diastotic power, which were significantly lower for malting
temperatures at and below 20oC.
Optimum moisture maintenance requires copious and frequent
watering during the turning operation. Turning and loosening the
germinating sorghum is essential to prevent malting of the rapidly
growing seedling, to reduce the resistance to aeration, and so assist the
uniform watering of the green malt. In germinating sorghum, both the
root and shoot protrude from the grain berry. The shoot is not
protected by the husk as in barley and in addition the seedling in
sorghum grows faster and more profusely. The seedling is thus for
more tender and prone to injury by abrasive turning. Injury to the
seedling and the tissue of the soft grain give rise to unproductive
regrowth of the seedling and give access to parasitic, potentially,
toxin-producing fungi. Furthermore the loss of the roots and shoots
cause losses of FAN essential for the opaque brewing process.
Malt quality increase rapidly during the initial phase of
malting, then remains static or even decrease with prolonged malting
(Novellie 1962 a, Dyer and Novellie, 1966). Loss of grain substance
by metabolic processes and formation of roots and shoots increase in
direct linear relation to malting intensity and time. The malting time
should be kept to the minimum required by the specified quality of the
malt and the relative importance of the critical component of the
quality.
2.3.2.3 Microbial infection
The conditions of high temperature and moisture in
combination with high microbial load, and the incidence of damage to
the seedling and the epidermis of the grain, favor the contamination of
the malting grain by potentially toxigenic fungi. Although floor and
industrially malted sorghum frequently contaminated by molds (Rabie
and Thiel, 1985), only about 10% of industrial malts were found to
contain more than 5 ppb, the legal limit of aflatoxin B over a period of
five years of intensive sampling. No aflatoxin was found in the opaque
beers (Trinder, 1988). Nevertheless, strict hygiene and selection of
clean sorghum of cultivars least susceptible to mold contamination are
essential. Surface-sterilization of the grain (e.g. formaldehyde and
hypochlorite) and strict control of the malting process can reduce
mold infection and proliferation.
2.3.2.4 Drying
At the end of malting, the malt is dried to 12% or less of
moisture. Drying should be rapid to avoid further metabolic losses and
to arrest microbial growth. Traditionally the green malt is dried in thin
layer in the sun-industrially the malt is dried in force-draft dryers with
high volumes of air heated to not more than 50oC. High temperature,
particularly during the initial stages of the process cause losses of
enzymes (Novellie 1962a; Okon and Uwaifo, 1985).
Malting and brewing technologies, like other technologies, are
not static but are continually changing. Because both technologies are
time-consuming research continues to seek ways to shorten processing
time while maintaining or even increasing quality of the end products.
Raising the temperature of steeping and/or germination above the
traditional 12 - 18oC range is attractive because significant malting
time can be saved. In general, steeping temperatures of up to 30oC
followed by germination at lower temperature (20oC), did not appear
to affect α-amylase synthesis (Baxter et al., 1980). Higher steeping
temperatures did have a detrimental effect on α-amylase levels,
however, α-amylase synthesis is quite sensitive to germination
temperatures, and even modest increases to 25oC significantly reduced
α-amylase levels in the final malt (Home and Linko, 1977).
Decreased moisture content of grain during steeping and germination,
however may lead to low levels of α-amylase in the `finished malt
(Brookes et al., 1976).
This may not be a problem when brewing with an all-malt
grist, but poor runoffs could occur when brewing with adjuncts.
The malting process is dependent upon the activities of α and β
amylases which are developed during germination (Novellie, 1960,
1962a).
2.4 Amylases
2.4.1 Historical
The amylase of wheat was probably the first enzyme to be discovered. It was observed to digest starch by
Kirchhoff in 1811. Leachs (1898) discovered the digestive action of saliva upon starch in 1831. Payen and Persoz (1876)
discovered malt amylase in 1833 and purified this enzyme by alcohol precipitation. In 1876 O'sullivan (1876) demonstrated
that when amylase acts upon starch the chief end product is maltose. In 1878 Marker (1878) stated that malt amylase is
composed of two different enzymes.
2.4.2 Sources of amylases
Amylases are found in nearly all plants, animals and
microorganisms. They occur in starchy seeds, and the amount
increases when the animals amylases occur in high concentration in
the pancreas.
Starchy substances constitute the major part of the human diet
for most of the people in the world , as well as many other animals.
They are synthesized naturally in variety of plants. Similar to
cellulose, starch molecules are glucose polymers linked together by
alpha 1-4 and alpha 1-6glucosidic bonds, as opposed to the beta 1-4
glucosidic bonds for cellulose.
Since a wide variety of organisms including humans, can
digest starch, alpha amylase obviously widely synthesized in nature
as opposed to cellulose for example human saliva and pancreatic
secretion contain a large amount of alpha amylase for starch digestion.
Alpha amylase depends on the sources of the enzyme.
Currently, to major classes of alpha amylases are commercially
produced through microbial fermentation. Based on the points of
attack in the glucose polymer chain, they can be classified in to two
categories, liquefying and saccharifying. Because the bacterial alpha
amylase attacks only alpha 1-4 bonds and it belongs to the liquefying
category. The hydrolysis reaction catalyzed by this class of enzyme is
usually carried out only to the extent, for example, the starch is
rendered soluble enough to allow easy removal from starch-sized
fabrics in the textile industry. The paper industry also uses liquefying
amylases on the starch used in paper coating where breakage in to the
smallest glucose subunits actually undesirable.
On the other hand the fungal alpha amylase belongs to
saccharifying category and attacks the second linkage from the nonreducing terminals (i.e C4 end) of the straight segment, resulting in
the splitting of two glucose units at a time of course, the product is a
disaccharide called maltose. Nam S.W. (undated).
Alpha amylases from cereal grains have been one of the most
widely studied groups of plant enzymes. The role that they play during
seed germination and technological processing of cereals has been the
subject of much research interest for over 100 years (Brown and
Morris, 1890).
2.4.3 Action
During the sprouting process α amylase is set free and
becomes active. Ford and Guthrie (1908) used papain to set α amylase
free. α amylase are dextrinizing, or starch-liquefying enzyme. They
hydrolyze glucosidic linkages in the middle portions of the starch
melecules and therefore are called endoamylases. The starch solution
which is being digested by α amylase soon ceases to give blue color
with iodine, α amylase produce α maltose. β amylases act on the ends
of starch molecules and are therefore called "exoamylases". These
amylases are saccharogenic in that they produce a considerable
amount of maltose; this is β-maltose.
Alpha amylases from cereal grains have been one of the most
widely studied groups of plant enzymes. The fact they play during
seed germination and technological processing of cereals has been the
subject of much research interest for over 100 years (Brown and
Morris, 1890). This enzyme responsible for the initial hydrolysis of
malt and adjunct starch during brewing. Therefore, a clearer
understanding of the factors controlling both α amylase synthesis in
cereal grains and starch hydrolysis by the enzyme would enable the
malting and brewing industries to utilize the enzyme morefully.
2.4.4 Properties of amylases
Many conditions such as mineral ions,pH,Temperature,and time in the
enviroment of amaylase affect their activities:
2.4.4.1 Time
A study conducted by Lasekan (1996) revealed that as
germination time for grains is extended, much α- amylase would be
produced. This was evident by the reduced viscosity in the flour paste
(Desikachar, 1980)
2.4.4.2 Temperature
Nearly all enzymes are irreversibly destroyed by heating upto
80oC and by this means can be distinguished from ordinary catalysts
with the regard to effects of temperature on sorghum germination in
the relation to amount of amaylase released, Palmer and Agu (1997)
found that a temperature of 30oC raised the level of produced αamylase compared to 20oC. In line of this the steeping temperature of
grains was detrimental in development of better germination, as
temperature of 25 oC reported to be optimum for gaining optimal malt
(Olaniyi and Monike,1987).
Alpha amylase of various sources has variable stability toward
heat treatment. Part of them for example bacterial alpha amylase, can
withstand higher temperature of processing.
2.4.4.3 Activation and inactivation
Different amylases from different sources require different
cofactors. This is mainly due to differences resulting from their amino
acids makeup which affect their activities. For example the majority