From waste to value: extraction of protease enzymes from Brewer’s spent yeast

This study investigates the potential of additive-free extraction techniques to produce a proteolytically active yeast extract for use in the food industry. Brewer’s spent yeast, a by-product of the brewing industry, is utilized as a feedstock, and thus a new route for its valorization is proposed. Four methods of releasing these components while maintaining their intrinsic bioactivity are investigated: thermal autolysis, ultrasonication, cell milling and high-pressure homogenization. Thermal yeast autolysis resulted in the highest release of protease activity, with 2.45 ± 0.05 U/g_dm after 3 h incubation at 45 °C. However, autolysis poses challenges for automation, and thus a stop criterion, due to the lack of in-line enzyme activity assays,. While glass bead treatment gave the highest reproducibility, ultrasonication and high-pressure homogenization resulted in comparably high protease activities in the BSY extracts produced. Both methods, in the form of a cell mill and high-pressure homogenizer, are cell disruption methods that are already employed on an industrial scale. It has now been demonstrated that these methods can be used to produce proteolytically active yeast extracts from a previously considered waste stream.