Solid State Fermentation of Brewer’s Spent Grain Using Rhizopus sp. to Enhance Nutritional Value

Abstract

In this study a valuable fermented brewer’s spent grain (BSG) was obtained by solid state fermentation (SSF) with Rhizopus sp. and assessed for feed and food applications. SSF conditions were optimized by factorial design and response surface methodology (RSM) to maximize the value of the resulting BSG biomass. Two Rhizopus sp. strains were tested as inoculum (one wild and one mutant strain) and time and temperature were analyzed. Measured response variables included, among others, protein content, soluble protein, degree of hydrolysis, antioxidant activity, total phenolic content and antibacterial activity. Both strains led to the highest protein concentration (31.7 ± 7.6%) and soluble protein (47.4 ± 3.8 mg/g DM) when BSG was fermented at 30 °C for 9 days. The biomass obtained presented a modified amino acid profile resulting in an essential amino acid index (EAAI) of 1.58 compared to FAO human nutrition standard, with antioxidant capacity (59.7 ± 7.7% DPPH reduction) and 11 times higher total polyphenol content (2.7 ± 0.1 mg GAE/g DM). Hereby, results demonstrate that SSF of BSG results in a significant increase of highly appreciated characteristics for feed or food applications, which could lead to a promising valorization alternative.