Sequential hydrolysis of spent brewer's yeast improved its physico-chemical characteristics and antioxidant properties: A strategy to transform waste into added-value biomolecules

The spent brewer's yeast (SBY) is a promising raw material due to its high content of proteins, but cells must be disrupted to release yeast compounds. Our work aimed to study the rupturing of SBY cell wall comparing conventional methods (autolysis and mechanical rupture) with enzymatic hydrolysis using proteolytic enzymes (Brauzyn®, Alcalase™, Protamex™ and Flavourzyme™). The susceptibility to rupture of different SBY by-products (repitched and non-repitched) and the effect of sequential enzymatic hydrolysis after rupture were also investigated. The hydrolysate produced at pH 5.5, 100% substrate concentration, 10% enzyme/substrate ratio and 60 °C resulted in maximized yield and enhanced antioxidant properties. Yeast compounds were more efficiently released after enzymatic hydrolysis, resulting in increases of 50% in crude protein, 83% in protein recovery and 63% in antioxidant properties. Repitched yeast took 3.5 longer to achieve the same degree of hydrolysis of non-repitched SBY. Sequential hydrolysis using Brauzyn® and Alcalase™ resulted in maximum solid recovery and antioxidant properties. An effective approach for the recovery of proteins and peptides of SBY while reducing environmental impact of beer production was presented. Additionally, we demonstrated that a process to reuse SBY must contemplate yeasts differences and their susceptibility to breakdown to be successfully implemented.