61A-29 |
Effect of malting on starch and its components in seven varieties of sorghum |
J. S. C. LEUNG and H. Corke. Botany, University of Hong Kong, Pokfulam Road, Hong Kong Sorghum is a major food crop ranking fifth in terms of world grain production. It has been used for centuries to brew opaque beer in South Africa. Being drought-tolerant and because of its low price, sorghum is suitable for further development of additional value-added uses. A better understanding of grain changes during brewing, for example in starch degradation, can help in further innovative development in the brewing industry. Our objective is to investigate the changes in starch and its components during five-day malting of seven sorghum varieties. Total starch was analyzed by Megazyme Assay Method. Amylose content and total sugar were determined by iodine binding and phenol-sulphuric acid test respectively. Reducing and non-reducing sugars were measured as described in AACC Method 80-60. a- and b-amylase were determined by Megazyme Assay Method and diastatic power was determined according to AACC Method 22-16. Reduction in viscosity after the addition of malt enzyme extract was measured by Rapid Visco Analyzer. Originally, the starch percentage of sorghum ranged from 62.3 to 74.4%, which decreased to 35.2 to 50.8% after malting, representing a decrease of 16.1 to 33.5%. This decrease in starch percentage was significantly correlated with the percentage increase in total sugar during malting. The amylose percentage of the sorghum starches ranged from 18.0 to 33.3%, indicating that these varieties had normal, nonwaxy endosperm. The amylose percentage then decreased to 10.1 to 24.2% after five-day malting, indicating that the amylose was hydrolyzed into its components during this period. Our results also showed that the optimum temperature of sorghum a-amylase was 55 to 59¢XC, and the diastatic power of the sorghum malt ranged from 28.7 to 57.6 SDU. By knowing more about the changes in starch characteristics of different sorghum varieties during malting and the enzymatic properties of sorghum malt produced, brewers can choose varieties that best suit their particular use.
Session 61A, Carbohydrate
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