Enzymatic Reduction of Anti-nutritional Factors in Fermenting Soybeans by Lactobacillus plantarum Isolates from Fermenting Cereals

Soybean is rich in dietary protein but contains some anti-nutritional factors (ANFs), including phytates, tannins, trypsin inhibitors and oligosaccharides. It is used with cereals in weaning foods to improve the protein content and supply essential amino acids. The objective of this work, therefore, was to use microorganisms, specifically Lactobacillus plantarum and the enzymes it produces to reduce anti-nutritional factors and improve the nutritional composition of such food blends. Nine strains of Lactobacillus plantarum isolated from spontaneously fermenting cereals, identified and characterised, were selected based on the abundant production of alpha-galactosidase for the fermentation of the legume. Samples were subjected to fermentation for 5 days and the reduction of anti-nutritional factors was monitored. Anti-nutritional factors and alpha-galactosidase were determined by UV-spectrophotometry. Data were analysed using ANOVA at p = 0.05. Fermentation reduced the tannin content in the raw samples from 1.93 to 0.12 mg/g. Phytate content reduced from 1.16 to 0.04 mg/g. The trypsin inhibitor and protease inhibitor also reduced from 1.20 to 0.010 and 1.2 to 0.020 respectively. The production of alpha-galactosidase by L. plantarum (1.8 unit/ml) enhanced the reduction while the nutritional composition of the food blend in which the soybean was added improved significantly. The use of alpha-galactosidase enzyme by Lactobacillus plantarum from local food sources is thus shown to reduce anti-nutritional factors in soybeans, which can be of benefit in enhancing the nutritional quality of cereal-legume gruels.