Glycerol catabolism by Pediococcus pentosaceus isolated from beer

Abstract

Among the lactic acid bacteria isolated from beer at different stages of elaboration, Pediococcus pentosaceus was the predominant species and the only that used glycerol as sole carbon source. Its utilization was studied in CAg strain growing on glycerol or on glycerol and limited concentration of glucose. Glycerol kinase and glycerol dehydratase pathways were responsible for glycerol degradation. On glycerol alone, the enzymatic activities of both pathways were expressed simultaneously and after glycerol consumption, the main products were acetate, 2,3-butanediol (2,3-BD) and 1,3-propanediol (1,3-PD). When the carbon sources were glycerol and glucose, glycerol was firstly degraded by the reductive pathway and after glucose consumption the activities of the glycerol kinase pathway were expressed. In this condition, glycerol was transformed into lactate, acetate, 2,3-BD and 1,3-PD. According to the enzymatic activities and fermentation balances, the production of acetate, providing ATP, can be correlated to lactate degradation, and the NAD required by these transformations could be obtained by the formation of 1,3-PD and 2,3-BD. Glycerol degradation should be correlated with the sensitivity of a beer to bacterial spoilage, and P. pentosaceus CAg considered as spoilage strain because it produces high volatile acidity and aroma compounds from glycerol conferring unacceptable flavour to beer.