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 environmentalimpact. One of the methods to add value and reduce environmental footprint is the generation of liquid yeast extractsintended 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. Priorto the scale-up valorisation of BSY, optimization of the physicochemical operational conditions of autolysis is required, asthese factors can significantly impact the yields and composition of the autolysate. In the present study, we investigated theeffects of temperature (40–50 °C), initial pH (3–8), and different pH control systems using autolysis buffers, on the releaseof solids and assimilable nitrogen content of the yeast Saccharomyces cerevisiae SafAle™ S-04, widely used by industrialand craft breweries in Argentina and worldwide. Our results allowed to analyse and compare a large number of experimentalvariables and find optimal conditions for autolysis performance. Autolysis carried out at 40 °C and pH 4 effectively facilitatesthe recovery of a high percentage of free amino nitrogen and autolysate was able to successfully support the fermentationprocess of S. cerevisiae var. Ethanol Red®, in the presence of a high initial concentration of sugar, exhibiting highly similarethanol yield compared to a commercial yeast extract. Liquid autolysates offer adequate nutritional quality for designingculture media for microorganism cultivation and facilitating various biotechnological processes.