61A-39 |
The combined effect of heat treatment and varying moisture content on the degree of starch gelatinization in whole cowpea seeds |
N. S. KOMEY, M. S. Chinnan, and R. D. Phillips. Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, GA 30223-1797 Previous studies have shown that steam treatment of cowpea seeds results in undesirable textural changes thought to be due to starch gelatinization in the outer layers of the seed. The dependence of starch gelatinization on initial moisture content has been reported for various cereal and cereal-legume flours. There is however, no information on the effect of a combination of moisture and heat on starch gelatinization in cowpea seeds. Investigate the effect of varying seed moisture content on the degree of starch gelatinization in steamed cowpeas. Cowpea seeds with moisture content between 10-40% were steamed at 100°C for 0-20 min and dried overnight at 55°C. The seeds were dehulled and fractionated into three layers – outer, middle and innermost. The degree of starch gelatinization was determined based on two methods: birefringence observation in cells under polarized light and amount of reducing sugars produced from enzymatic (pullulanase and b-amylase) hydrolysis. Examination of the starch cells under polarized light showed a typical loss of birefringence associated with starch gelatinization. This loss of birefringence was more visible as steaming time and initial moisture content increased indicating increased starch gelatinization. The outer layers of the seed also showed less birefringence as compared with the underlying layers. Enzymatic hydrolysis of samples with 10% moisture content confirmed the results obtained by microscopic examination. However, a different trend was observed in samples steamed at higher initial moisture content, where increased steaming time resulted in decreased susceptibility to enzymatic hydrolysis in all the layers. The results suggest that increasing the moisture content prior to steaming could have led to the formation of enzyme resistant starches. This might have implications on the textural characteristics and insect susceptibility of the cowpea seeds.
Session 61A, Carbohydrate
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