Impact of solid-state fermented Brewer's spent grains incorporation in biscuits on nutritional, physical and sensorial properties

Brewer's spent grains (BSG) is the abundant food processing by-product of beer production yet its application in food is limited due to its high susceptibility to microbial putrefaction and undesirable effect on the colour, structure and texture. Solid-state fermentation of BSG with Rhizopus oligosporus (RO) may further improve the nutritional, structural and textural properties of BSG-containing foods thus this study developed fermented BSG-containing biscuits and assessed their nutritional, physical and sensorial properties. Control (no substitution), autoclaved BSG (AB)- and fermented BSG (ROB)-containing biscuits (15/30% wheat flour substitution) were prepared. 30% ROB showed the greatest improvement in nutrient composition and anti-oxidant capacity. In vitro starch digestibility was significantly lowered in 30% ROB than Control, which can be explained by the greatest α-glucosidase inhibition activity of 30% ROB. BSG-containing biscuits were darker, less hard and more fracturable than Control, with no difference between ROB and AB, and gave better Just-about-right score for hardness. However, flavour and overall liking scores were lower in 30% AB and 30% ROB than lower substitution biscuits. Collectively, fermented BSG-substituted biscuits resulted in acceptable flavour and texture, as well as greater improvements in nutrient composition, anti-oxidant capacity, α-glucosidase inhibitory activity and in vitro starch digestibility.