Effect of fermentation on protein digestibility of soybean and sweet potato blends: aspergillus oryzae vs. Lactobacillus plantarum
Kiplamai, F. K.
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The improvement of nutritional quality of foods through fermentation has been practiced for long. Fermentation imparts desirable characteristics to products and makes them more utilizable nutrient sources than the unfermented products. Sweet potatoes have been under utilized industrially and are mainly used at household level. Soybeans are rich in proteins but their full utilization has been hampered by their anti-nutritional properties which are destroyed by heating and fermentation. The purpose of this study was to produce suitable blends of soybean and sweet potato flours targeted at alleviating protein related malnutrition. The quality characteristics of the fermented and unfermented soybean and sweet potato composite flours were compared. The fermentation with Lactobacillus plantarum was at 370C for 168 hours with sampling every 24 hours. The Aspergillus oryzae fermentation was performed at 250C for six weeks with samples taken weekly for laboratory analysis. In-vitro protein digestibility was determined enzymatically. The data obtained was subjected to General Linear Model (GLM) of the Statistical Analysis System (SAS). Protein digestibility was improved by an average 4% (p< O.05) in the bacterial fermented composites and by an average of 5.5% (p< O.05) in the composite flours fermented with the mould. The composite containing 50% soybean and 50% sweet potato reflected higher protein digestibility than the composite with 25% soybean and 75% sweet potato. Fermentation significantly increased protein digestibility but an initial drop was observed in the higher (50% soybean and 50% sweet potato) protein composite for both bacterial and mould fermentations. Optimum protein digestibility improvement was achieved thus a baseline for development of suitable blends targeting protein malnutrition.