Inhibiting malate metabolism in L. plantarum 299v by introducing lactic acid in ProViva apple drinks

Abstract: This master thesis aimed to evaluate the possibilities of inhibition of Lactobacillus plantarum 299v metabolism of malate by introduction of lactic acid in ProViva apple drinks. The malate metabolism of L. plantarum have been found to promote an overproduction of carbon dioxide in ProViva apple drinks and thereby the metabolism was tried to be inhibited. The experiment included three different concentration of apple juice in combination with three different concentrations of lactic acid. This lead to a total of nine different apple drinks to examine and the drinks were evaluated with respect to carbon dioxide production, pH changes and organic acids alternations. Besides this, the amount of live probiotics and the absence/presence of molds and yeast were documented. The analyses were performed specific days from the drinks had been produced until the drinks had been stored in 8oC for 36 days. Sensorial analysis were performed to highlight possible flavor differences during storage and also to grade the different drinks with respect to how tasty they were. It was found that the concentration of lactic acid does affect the L. plantarum and its metabolism. The bacterium was inhibited in growth due to the addition of lactic acid and the gas formation was decreased. It was also found that with a lactic acid concentration equal to or above 7g/l the L. plantarum started to die. At the same time a lactic acid concentration of 4g/l seemed to be a promising concentration for a future ProViva apple drink. The sensory analysis showed that no significant difference in organoleptic properties could be found during the storage of the drinks. The amount of added lactic acid to the apple juices did not significantly matter for the shelf life of the drinks since the yeast and mold present in the analysis appeared to occur randomly.