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

Abstract

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 8317Ug1 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 8000U of cellulase kg1 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±1g) for 66days. 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 (p0.05) of European seabass but increased feed efficiency (up to 18%; p<0.05) and protein utilization (up to 22%; p<0.05). Nitrogen retention and total alkaline proteases activity were higher in fish fed with the PreBSG4 and PreBSG8 diets (p<0.01) than with the BSG4 and BSG8 diets. In contrast, BSG4 and BSG8 diets increased plasma glucose and decreased cholesterol levels compared to the control (p<0.05). In conclusion, this work showed the effectiveness of an extract produced by SSF of BSG, with high carbohydrases activity, to enhanced feed and protein utilization by European seabass, without affecting growth performance. Moreover, using BSG-extract to pre-treat PF seems to be more effective in improving protein utilization than adding it directly to the diet. This study demonstrated the feasibility of BSG valorization through SSF to produce a functional additive for aquafeeds. The novel produced BSG-extract simultaneously contributes to the sustainability of resources in a circular economy approach and increases the nutritional value of plant feedstuffs.