Valorization of Spent Brewer's Yeast by Pulsed Electric Field Treatment Combined with Enzymatic Hydrolysis

Spent brewer's yeast, a major by-product of the brewing industry, is a valuable source of bioactive compounds. The main technological limitation for their recovery is the rigid yeast cell wall, while the high nucleic acid content may restrict the direct use of yeast-derived extracts for human nutrition. In this study, pulsed electric field (PEF) treatment, applied alone or in combination with enzymatic hydrolysis, was investigated for the production of yeast-derived extracts with different compositions. PEF treatment performed in continuous-flow mode resulted in more than 98% of cells with irreversibly permeabilized membranes and enabled the rapid and selective release of low-molecular-weight intracellular compounds during subsequent incubation of the cells in water. Within 4 h, approximately 61% of total antioxidant activity, 65% of glutathione, and around 80% of free α-amino nitrogen and B-group vitamins were recovered at different rates, while the aqueous extracts were characterized by low purine nucleotide content. Electropermeabilized cells exhibited high sensitivity to enzymatic hydrolysis. After 6 h of incubation with 0.2% (v/v) Alcalase, the obtained hydrolysates contained 254 ± 17 mg/g DCW of protein, mostly in the form of peptides, 148.2 ± 17.3 mg/g DCW of free α-amino nitrogen, and a total phenolic content of 16.7 ± 1.9 mg GAE/g DCW. The maximal antioxidant activity (62.7 ± 9.3 mg TE/g DCW) was reached after 4 h of incubation, corresponding to a 2.7-fold increase compared with cell lysates. Overall, PEF treatment, applied alone or in combination with enzymatic hydrolysis, provides an efficient and mild approach for the production of yeast-derived extracts with tailored compositions and potential applications in the food, pharmaceutical, and cosmetic industries.