Brewer’s spent yeast (BSY) is produced by the beer industry and has high nutritional value and great potential for producing high-value molecules, such as peptides, for nutraceutical, food and feed applications. In the present research, Flavourzyme® and Protamex® enzymes were selected for protein hydrolysis based on previous studies. The optimum conditions for the enzymatic hydrolysis were defined by response surface methodology (RSM) by the Box–Behnken design composed of four variables: temperature, pH, enzyme dosage and time. Protein content, hydrolysis degree and the anti-microbial and antioxidant bioactivities of obtained hydrolysates were quantified. Obtained results show that time, enzyme dosage and pH had the highest effect on protein extraction yield (PEY), degree of hydrolysis (DH) and antioxidant activity. Response variables ranged from 13.7 to 29.7% for PEY, from 6.3 to 35.7% for DH and from 0.65 to 1.65 g for Trolox equivalent antioxidant capacity. Antimicrobial activity, measured as minimum inhibitory concentration, against Aeromonas salmonicida, Bacillus cereus, Bacillus subtilis and Salmonella enterica, ranged from 6.25 to 50 mg/mL. Antioxidant and antimicrobial activity showed the potential use of BSY hydrolysates as an ingredient for functional foods.

Lignin in animal diets is a limiting factor due to its low digestibility. This study assessed the effects of thermal or mechanical pre-treatments and enzymatic hydrolysis on spent coffee grounds’ (SCG) nutritional value and digestibility. A first trial studied the effect of thermal pre-treatment and hydrolysis with removal of the liquid part and a second trial studied mechanical pre-treatment and hydrolysis with and without removal of the liquid part. Autoclaving did not improve the enzymatic performance nor the nutritional value. Hydrolysis reduced the digestibility of the solid phase and impaired its ruminal fermentation efficiency. Hydrolysates without removing the liquid part improved its nutritional value, but not compared with unprocessed SCG. Grinding increased crude protein and reduced crude fibre and protein, which led to greater fermentation and in vitro digestibility. Thus, grinding emerges as the most promising valorisation strategy to improve SCG nutritional characteristics and their use for animal feed, contributing to the circular economy.

Grape stems are a by-product of wine production which is managed as a waste. Animal feeding arises as a potential alternative. However, its practical use may be compromised by its high lignin content. In this sense, hydrolysis emerges as a strategy to increase fibre digestibility. In addition, due to its high and variable moisture content, it should be dried to prevent microbial deterioration and a washing pre-treatment to reduce sugar content becomes necessary to minimize drying problems due to sugar melting at high temperatures. Within this framework, this study assessed the effect of washing and three different hydrolysis on the nutritive value of grape stems. A factorial design was carried out, with washing (with or without) and hydrolysis (without, enzymatic, alkali, and alkali-enzymatic) as factors. When the washing pre-treatment was not applied, only the alkali hydrolysis process maintained in vitro digestibility, but at the expense of a lower fermentation efficiency. When the washing pre-treatment was applied, fibre contents were similar among hydrolysis processes, but the alkali hydrolysis improved in vitro digestibility with similar fermentation efficiency. In conclusion, the alkali hydrolysis maintained or improved the grape stem nutritive value depending on whether the washing pre-treatment was applied or not.