Effect of Fermentation on Chemical Composition and Nutritional Quality of Extruded and Fermented Soya Products

The effect of fermentation on chemical composition, amino acid profile and protein digestibility of extruded soya protein products was investigated. The soya protein products (low moisture extruded soya product, medium moisture extruded soya product, high moisture extruded soya product, soya meal and soya kernel) were fermented with Bacillus natto from small and large brands of soya bean cultivar. The protein content (%) ranged from 38.20 to 62.98 with the highest content in the high moisture extruded protein product fermented with Bacillus natto from large brand of soya bean cultivar. Contents of carbohydrates ranged from 14.77 to 29.08 while those of crude fibre, fat and ash were generally low. Fermentation improved protein digestibility in the raw soya meal and kernel than in the unfermented extruded and extruded fermented products. Extrusion reduced the nitrogen solubility index of the extruded samples. The contents of amino acids except arginine increased in all the samples after fermentation. Trypsin inhibitor activity decreased from 27.33 TIU/g in the unfermented soya sample to between 1.58 and 18.5 TIU/g after fermentation, whereas there was a decrease in phytic acid content only in the fermented soya meal and low moisture extruded soya sample.