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
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