Effect of Soaking, Germination and Microwave Cooking on Flatulence-Causing Oligosaccharides of Certain Legumes

Abstract

The effect of soaking, germination, ordinary and microwave cooking on oligosaccharides in some commonly legumes namely; faba bean, mung bean, cowpea and kidney bean were investigated. HPLC determination showed that raffinose family oligosaccharides (RFOs); (raffinose, stachyose and verbascose) constituted 47-61% of soluble carbohydrates in the studied legumes. Raw kidney bean contained the highest amount of oligosaccharides compared with other tested legume seeds. Soaking for 12 h in tap water (25ºC±2) led to losses in total RFOs by 21, 24, 23 and 25% in faba bean, mung bean, cowpea and kidney bean, respectively. The highest losses were found in raffinose (26%) and stachyose+verbascose (28%) in mung bean and cowpea, respectively. Germination of seeds indicated that there were significant reductions in the concentration of sucrose and RFOs. As the period of germination was elongated, the concentration of the oligosaccharides declined further. Ordinary and microwave cooking of raw and soaked seeds lowered RFOs content in all investigated legumes. Ordinary cooking of raw and soaked legumes caused losses of total RFOs amounted up to 15-39% and 17-42%, respectively. The reductions of total RFOs were 33-44% after microwave treatment of its initial content in soaked legume seeds. The combined effect of soaking and microwave cooking of seeds caused further removal of RFOs by 42-60% losses of its initial content in raw samples. It may be concluded that germination and microwave cooking of food legumes caused considerable losses of total oligosaccharides as well as reducing flatus-causing agent.