Reduction of oligosaccharide content of soybeans by the action of <i>Lactobacillus plantarum</i> isolated from fermented cereals

Abstract

Most African foods used in weaning are usually fermented cereals which supplies mainly carbohydrate. Unless these are supplemented with other nutrient sources, they may lead to excessive intake of carbohydrate which might cause malnutrition in growing children. Minimum dietary requirements of a child for protein could be met through fortification with legumes like cowpea, peanuts or soybeans but they contain raffinose family of oligosaccharide (RFOs), which are responsible for gas formation, bloating and flatulence in children. This work aims at using Lactobacillus plantarum and the enzyme α- and β-galactosidases it produces, to hydrolyse raffinose to simple sugars and hence improve the raffinose-containing weaning foods. Three strains of L. plantarum obtained from fermented cereal gruels and identified using both classical and molecular methods were selected after screening for their ability to produce these enzymes in abundance. They were used to ferment different combinations of cereals and legumes. The oligosaccharide profile before and after the various pre-treatment methods and fermentation were determined using gas chromatography with flame ionization detector (GC-FID). Data obtained were analysed using ANOVA at p < 0.05. Fermentation for 120 h with L. plantarum reduced the total RFO content of soybeans to different levels in the samples. Losses of 30, 28 and 37% in stachyose, raffinose and verbascose, respectively were observed in the fermented raw samples; 72, 58 and 41% reduction in the fermented cooked samples and 76, 68 and 71% reduction in the roasted samples relative to the untreated samples. The use of galactosidase enzymes by L. plantarum from fermented cereals reduced the raffinose-oligosaccharide profile with simultaneous increase in reducing sugar levels. Adequate weaning foods can be prepared with such and the problem of bloating, gas production and flatulence can be solved by the action of L. plantarum in legume-cereal blends.

Keywords: Raffinose-oligosaccharides, soybeans, fermented cereals, Lactobacillus plantarum, alpha-galactosidase, weaning foods

African Journal of Biotechnology, Vol 13(37) 3790-3796