Brewers’ Spent Yeast and Grain Protein Hydrolysates as Second-Generation Feedstuff for Aquaculture Feed

Aquafeeds are formulated to contain all the essential nutrients that fishes need to keep healthy. They are highly dependent on marine ingredients: fish meal and oil. Hence, alternative ingredients which successfully replace these marine ingredients are required to result in sustainable and economical feeds. In this context, brewers’ by-products arise as alternative potential ingredients to fish meal in aquafeed due their availability and nutritional content. However, reducing aquaculture’s dependence on marine resources depends not only on developing alternative ingredients but also on improving their nutritional efficiency. In this context, Life Brewery project (LIFE16ENV/ES/000160) proposes an enzymatical hydrolysis step prior to the stabilization process to improve the digestibility of brewers’ by-products and, therefore, increases the assimilation of nutrients by fishes. Hence, optimum hydrolysis conditions for both brewers’ spent grain and yeast have been defined by comparing different enzymes combination and hydrolysis conditions at laboratory scale. Afterwards, selected enzymes and conditions have been validated at industrial scale. Finally, the digestibility of different experimental diets containing both hydrolysed and non-hydrolysed ingredients from brewers’ waste has been determined with positive results. Obtained results showed that the inclusion of brewers’ spent yeast and spent grain in aquafeeds for gilt-head sea bream show a good protein digestibility and can be considered as suitable ingredients to successfully replace fish meal in aquafeed diets.