Impact of Solid State Fermentation on Nutritional and Physical Properties of Food Containing Brewer’s Spent Grains

Abstract

Abstract Objectives Brewer's spent grains (BSG), the key food processing by-product of beer manufacturing, is rich in dietary fiber and protein. However, BSG has limited use in food production due to its poor digestibility and texture. Therefore, this study aimed to investigate the effects of Rhizopus oligosporus (RO) solid-state fermentation (SSF) on the nutritional and physical properties of BSG containing food. Methods Autoclaved BSG (AUBSG) was obtained via sterilization of raw BSG (UBSG). SSF with RO inoculation at 2% (w/w) on AUBSG was conducted to produce 2% ROUBSG. AUBSG and 2%ROUBSG substituted biscotti (AUB and ROUB respectively) were developed by substituting 30% of wheat flour while control biscotti (C) was made with wheat flour only. Crude protein, dietary fiber (total – TDF, insoluble – IDF, soluble – SDF), fat, ash, available carbohydrates (ACHO), phytic acid and anti-oxidant capacity were analyzed for UBSG, AUBSG and 2%ROUBSG. Nutritional properties, in vitro starch digestibility and physical properties, including loaf height, hardness and fracturability, were also analyzed for AUB, ROUB and C. Statistical significant difference (p ≤ 0.05) was determined via one-way analysis of variance, followed by Tukey post hoc test. Results Compared to AUBSG and UBSG, 2%ROUBSG showed nutritional improvement with significantly higher crude protein, SDF, anti-oxidant capacity and lower phytic acid and ACHO. When compared to C, both ROUB and AUB had significantly higher crude protein, TDF, IDF, anti-oxidant capacity as well as significantly lower ACHO and slower rate of in vitro starch digestion. Further improvement of crude protein, anti-oxidant capacity and phytic acid was also observed in ROUB as compared to AUB. For physical properties, ROUB showed no significant difference in hardness and fracturability from C and significantly higher loaf height than AUB. Conclusions Findings from this study reveal the beneficial effect of SSF in improving nutritional properties of BSG along with enhancement of nutritional and physical properties of BSG incorporated food. This study may suggest the viability of such fermentation technology in upcycling food by-product into nutritious food ingredients. Funding Sources Singapore Ministry of Education, National University of Singapore.