Effect of soaking, cooking and germination on the oligosaccharide content of selected Nigerian legume seeds

The identity and quantity of and effect of processing on raffinose oligosaccharides in raw, mature seeds of lima beans (Phaseolus lunatus), pigeon peas (Cajanus cajan), African yam beans (Sphenostylis sternocarpa) and jackbeans (Canavalia ensiformis) were investigated. Sucrose, raffinose, stachyose and verbascose were identified by HPLC in all the legume seeds. The total alpha-galactoside contents of the seeds in decreasing order were African yam beans 3.84 mg/100 mg; white lima beans 3.62 mg/100 mg; cream pigeon peas 3.51 mg/100 mg; red lima beans 3.37 mg/100 mg; jackbeans 2.83 mg/100 mg and brown pigeon peas 2.34 mg/100 mg. The predominant oligosaccharide was verbascose in pigeon peas and stachyose in the other three legumes. Cooking unsoaked seeds brought about a greater reduction in the total alpha-galactoside content than soaking for nine hours. The removal of oligosaccharides was higher in legumes cooked in alkaline solution than in water. Germination quantitatively reduced raffinose, stachyose and verbascose while sucrose was increased in all seeds except red lima beans and jackbeans.