Application of fermented brewer's spent grain extract in plant-based diets for European seabass juveniles

This work aimed to evaluate the potential of a carbohydrases-rich extract produced by SSF of BSG to enhance the nutritional value of plant-based diets for European seabass (Dicentrarchus labrax) juveniles. BSG was fermented by A. ibericus (MUM 03.49) to obtain an aqueous enzymatic extract (1178 and 8317 U g−1 cellulase and xylanase activity, respectively). A control (50% protein; 18% lipids) diet was formulated with 55% DM of plant feedstuffs (PF), and four other diets were formulated similarly to the control but including 0.4% and 0.8% DM of lyophilized extract (BSG-extract), corresponding to 4000 and 8000 U of cellulase kg−1 of diet, directly included in the diet (BSG4 and BSG8 diets) or used to pre-treat the PF mixture of the control diet (PreBSG4 and PreBSG8 diets). Pre-treatment of PF with BSG-extract increased three-fold the dietary reducing sugars content and two-fold the antioxidant activity than the control diet. Cellulase and xylanase activities were highest in diets including BSG-extract directly added than pre-treated PF diets. These diets were fed to European seabass (IBW = 22 ± 1 g) for 66 days. Dietary supplementation with BSG-extract, mixed in the diet or used as a pre-treatment of PF, did not affect growth performance and whole-body composition (p>0.05) of European seabass but increased feed efficiency (up to 18%; p