Apple juice as a medium for fermentation by the probiotic Lactobacillus plantarum PCS 26 strain

Abstract

Studies on the development of non-dairy probiotic foods and beverages are continuously emerging. Fruit and vegetable juices have proved to be promising carriers or growth media for probiotics. In this study, apple juice was explored as a growth medium for cultivation of the probiotic Lactobacillus plantarum PCS 26 strain. Fermentation was performed with free and Ca-alginate–embedded bacteria at different initial pH values, as well as with whey supplementation as a growth enhancer. During the fermentation, growth kinetics, pH, sugars consumption and lactic acid production were measured, along with culture survival during storage. The best results were achieved by fermentation at an initial pH of 4.2, reaching maximal cell density of 2.5 x 10⁹ CFU/mL and a final pH of 4.7 after 24 h. Malolactic conversion was commenced by the strain as energy yielding mechanism, thereby lowering the consumption of sugars below the limit of determination by the analytical method used. Apple juice supplementation with 5 % v/v whey accelerated fermentation kinetics and resulted in a higher viable bacterial count. In contrast, entrapment of cells into Ca-alginate caused significantly slower growth, yielding a lower bacterial count at the end of fermentation (3.2 x 10⁶ CFU/mL). However, stability during storage of the fermented product at 4–7 °C improved, and the survival of immobilized bacteria, estimated by Weibullian model, increased to 32.1 ± 5.2 days compared to 22.0 ± 0.68 days in the free-cell fermentation. In conclusion, apple juice was found to be an appropriate medium for fermentation by probiotic Lactobacillus plantarum PCS 26, resulting in a functional drink with potentially good sensory acceptance and shelf life.