Adaptation to sorbic acid in low sugar promotes resistance of spoilage yeasts to the preservative

The weak acid sorbic acid is a common preservative used in soft drink beverages to control microbial spoilage. Consumers and industry are increasingly transitioning to low-sugar food formulations, but potential impacts of reduced-sugar on preservative efficacy are barely characterised. In this study, we report enhanced sorbic acid resistance of spoilage yeasts in low-glucose conditions. We had anticipated that low glucose may induce respiratory metabolism, previously shown to be targeted by sorbic acid. However, a shift from respiratory to fermentative metabolism was correlated with the sorbic acid resistance in low glucose. Fermentation-deficient yeast species did not show the low-glucose resistance phenotype. Phenotypes observed for certain yeast deletion strains suggested roles for glucose signalling and repression pathways in the sorbic acid resistance at low glucose. This low- glucose induced sorbic acid resistance was alleviated by supplementing yeast cultures with succinic acid, a metabolic intermediate of respiratory metabolism (and a food-safe additive) that promoted respiration. The results indicate that metabolic adaptation of spoilage yeasts promotes sorbic acid resistance at low glucose, providing new insight into potential spoilage, and preservation, of foodstuffs as both food producers and consumers move towards a reduced-sugar landscape.