Effect of solid-state fermentation of Brewer's spent grain on digestibility and digestive function of european seabass (Dicentrarchus labrax) juveniles

This study assessed the effects of dietary inclusion of solid-state fermented (SSF) brewer’s spent grain (BSG) with Aspergillus ibericus on nutrient and energy digestibility, digestive enzyme activity, and intestinal histomorphology of juvenile European seabass (Dicentrarchus labrax). Five diets (18 % crude lipids and 45 % crude protein) were formulated, including a control diet (without BSG), two diets with 10 % and 20 % unfermented BSG (10BSG and 20BSG), and two other diets with 10 % and 20 % fermented BSG (10BSG-SSF and 20BSG-SSF). SSF affected the BSG's nutritional composition, including a 21 % increase in protein content and reductions in lipid (49 %), cellulose (30 %), hemicellulose (34 %), and lignin (7.3 %) content. Antioxidant activity and total phenolic compounds were minimal before SSF but significantly increased after SSF. Dietary incorporation of 20 % BSG-SSF increased the digestibility of dry matter (p<0.01), protein (p=0.03), isoleucine (p=0.03), glutamate (p=0.02), lipids (p=0.04) and energy (p=0.04) compared to the 20BSG diet. Moreover, SSF also modulated digestive enzyme activity, reducing total protease (p=0.03) and trypsin (p=0.01) activities in fish fed the 10BSG-SSF diet compared to the control diet. Fish fed the 20BSG diet showed changes in intestinal histomorphology compared to those fed the control diet, and SSF of BSG appeared to mitigate these effects.

Overall, these results indicate that SSF is a promising technique for enhancing the nutritional quality of low-value agro-industrial by-products, such as BSG, increasing their potential use as feed ingredients and contributing to reducing the climate and environmental footprint of aquaculture production.