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

The identity and quantity of and effect ofprocessing 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 byHPLC in all the legume seeds. The totalα-galactoside contents of the seeds in decreasing order were African yam beans3.84 mg/100 mg; white lima beans 3.62 mg/100 mg; creampigeon peas 3.51 mg/100 mg; red lima beans3.37 mg/100 mg; jackbeans 2.83 mg/100 mg and brownpigeon peas 2.34 mg/100 mg. The predominantoligosaccharide was verbascose in pigeon peas andstachyose in the other three legumes. Cooking unsoakedseeds brought about a greater reduction in the totalα-galactoside content than soaking for ninehours. The removal of oligosaccharides was higher inlegumes cooked in alkaline solution than in water.Germination quantitatively reduced raffinose,stachyose and verbascose while sucrose was increasedin all seeds except red lima beans and jackbeans.