Brewers’ spent grain liquor as a feedstock for lactate production with Lactobacillus delbrueckii subsp. lactis

Abstract

Brewers’ spent grain (BSG) is a low-cost by-product of the brewing process. BSG liquor names the liquid components of BSG, mainly glucose, maltose, and long-chain α-1,4-glycosidic bond glucose oligomers. These substances should be separated in existing BSG biorefineries, as they might lead to an increased formation of microbe-inhibiting compounds in well-established hydrothermal/enzymatic saccharification processes. In most cases, this liquid fraction is discarded. The present study presents for the first time an optimized process with BSG liquor for the purpose of producing bulk chemicals (e.g., lactate) in relevant concentrations. The process comprises the application of yeast extract, produced from own brewing processes, as the sole supplemented complex constituent in a simultaneous fermentation and saccharification process. Kinetic parameters for the final optimized process conditions with the organism Lactobacillus delbrueckii subsp. lactis were: maximum specific growth rate µmax = 0.47 h−1, maximum lactate concentration cLac, max= 79.06 g L−1, process yield YPS= 0.89 gLac gSugar−1, lactate production rate qP = 4.18 gLac gCDW−1 h−1, and productivity P15 h= 4.93 gLac L−1 h−1. BSG liquor, linked with yeast extract from Brewers’ yeast, can be a promising substrate for further bioprocess engineering tasks and contribute to a holistic and sustainable usage of Brewers’ spent grain.