Survival of Listeria innocua in apple juice as affected by vanillin or potassium sorbate

Survival of stationary phase Listeria innocua (as surrogate microorganism for L. monocytogenes) inoculated in apple juice (pH 3.3 or 3.8) supplemented with vanillin (1, 500ppm or 3, 000ppm) or potassium sorbate (500ppm or 1, 000 ppm) and stored at room temperature was studied. L. innocua survived in apple juice without the preservatives at pH 3.3 or 3.8, with minimal population reductions. In the juices with the incorporation of potassium sorbate or vanillin, L. innocua behavior depended on the pH value, the type of antimicrobial and its concentration. At pH 3.3, the presence of vanillin (3, 000 ppm) or potassium sorbate (1, 000 ppm or 500 ppm) decreased L. innocua counts, with population reductions ranging from 4 to 5 log cycles after a 4 h - 8 h exposure at 30C. However, at pH 3.8, L. innocua showed sensitivity only to 3, 000 ppm vanillin. Survival curves were successfully fitted using a Weibull type distribution of resistances. The results suggest that the use of potassium sorbate or vanillin could prevent the survival of L. innocua in contaminated unpasteurized and pasteurized apple juice. Vanillin, a natural antimicrobial, would be particularly suitable as an antilisterial additive for less acidic apple juice.