Phytochemical Analysis and Characterisation of Brewers’ Spent Grain Properties as Affected by Fermentation and Ultrasonication Pretreatments

Brewers’ spent grain (BSG) is a highly abundant, nutrient-rich by-product generated by the brewing sector. Upcycling and reusing by-products from the food sector have become necessary to achieve sustainable food security globally. This research investigated traditional and novel pretreatments to modify the properties of BSG for better utilisation as a food ingredient. In this study, BSG was ground and subsequently processed in two different ways: ultrasonicated for 15 min and fermented with lactic acid bacteria for 24, 48, and 72 h. Influences of fermentation and ultrasonication on the antioxidant activity, thermal properties, colour, chemical composition, total phenolic content (TPC), and total flavonoid content (TFC) were then investigated. There was a general increase in the antioxidant properties of BSG flour ultrasonicated for 15 min (FRAP, 4.35 mgTE/g; DPPH, 65.87%; ABTS, 37.29%) and fermented BSG flour fermented with Lactococcus lactis (48 h) (FRAP, 2.29 mgTE/g; 63.93%; 24.48%) compared to native BSG (2.10 mgTE/g, FRAP; 65.87%, DPPH; 23.50%, ABTS). The highest percentage of fibre (28%) was observed in BSG fermented for 24 h. There was also increase in colour value (L*, 56.33–59.07; a*, 3.18–3.65; b*, 9.61–10.70), TPC, and TFC (0.13–0.16 and 0.37–1.30, respectively), and variations in peak intensities on the thermogram. These results indicate that ultrasound and fermentation are promising technologies for the enhanced valorisation of BSG for value-added food product development.