Liquid extract with high amino nitrogen obtained by autolysis of brewing yeast can be used as supplement for bioethanol production

Abstract

Brewer’s spent yeast (BSY) is a commonly underutilized by-product of the brewing industry with a highly negative environmental impact. One of the methods to add value and reduce environmental footprint is the generation of liquid yeast extracts intended for formulating culture media for the propagation of microorganisms of biotechnological and agro-industrial interest. Autolysis is the most commonly employed non-mechanical process for the industrial production of yeast extracts. Prior to the scale-up valorisation of BSY, optimization of the physicochemical operational conditions of autolysis is required, as these factors can significantly impact the yields and composition of the autolysate. In the present study, we investigated the effects of temperature (40–50 °C), initial pH (3–8), and different pH control systems using autolysis buffers, on the release of solids and assimilable nitrogen content of the yeast Saccharomyces cerevisiae SafAle™ S-04, widely used by industrial and craft breweries in Argentina and worldwide. Our results allowed to analyse and compare a large number of experimental variables and find optimal conditions for autolysis performance. Autolysis carried out at 40 °C and pH 4 effectively facilitates the recovery of a high percentage of free amino nitrogen and autolysate was able to successfully support the fermentation process of S. cerevisiae var. Ethanol Red®, in the presence of a high initial concentration of sugar, exhibiting highly similar ethanol yield compared to a commercial yeast extract. Liquid autolysates offer adequate nutritional quality for designing culture media for microorganism cultivation and facilitating various biotechnological processes.