46I-14 |
Milling and heat processing effect on cyanogenic glycoside and haemagglutinin levels in a lima bean (Phaseolus lunatus)variety |
L. L. NIBA, Department of Human Nutrition, Foods & Exercise, Virginia Polytechnic Institute and State University, 319 Wallace Hall, Virginia Tech, Blacksburg, VA 24060 and C. C. Onuoha, University of Nigeria, Nsukka, Nigeria. Lima beans (Phaseolus lunatus) are a major source of dietary protein and energy in most tropical areas. Some varieties however, contain high levels of toxicants, notably cyanogenic glycosides and heamagglutinins, which elicit adverse physiological effects such as neurological and growth impairment. Reduction of toxicants is therefore essential to improve the utilization of these varieties. The objective of this study was to ascertain the levels of cyanogenic glycosides and haemagglutinins in a commonly consumed lima bean variety, and determine the effect of readily accessible milling and heat procedures on toxicant levels. A variety of lima bean (Phaseolus lunatus) seeds were either cooked whole, or milled into flour prior to soaking, cooking and drying. Proximate composition was determined by approved methods. Cyanogenic glycoside content was determined by enzyme hydrolysis. Haemagglutinin activity was determined by a micro-titre procedure using precipitated erythrocytes of blood group A. The beans contained 24.7 g /100 g protein, 2.8 g/100 g fat and 3.0 g/100 g crude fiber. Cyanogenic glycoside content of raw beans was 260 mg/100g, and reduced to less than 100 mg/100g after six hours of cooking. Cyanogenic glycoside content of soaked lima bean flour was 37 mg/100g after six hours, and 41 mg/100g in the cooked flour. Drying of the flour after soaking or cooking further reduced cyanogenic glycoside levels. Raw beans had high haemagglutinin activity, causing agglutination at even very low concentrations. Cooking for five hours diminished agglutinating activity. The results indicate that milling beans into flour and application of heat are effective in reducing anti-nutrients to safe levels, ensuring detoxification. This in turn will mitigate the effects of intoxication and optimize lima bean utilization as source of protein.
Session 46I, Toxicology & Safety Evaluation
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