An innovative edible coating, made from food grade polyvinyl alcohol (PVOH) and gelatin hydrolysates (HGel), was evaluated as a carrier of Lactococcus lactis acting as anti-listeria protective culture for refrigerated foods. The coating was applied on a compostable polylactic acid film surface and its anti-listeria activity was evaluated at 4 °C in a liquid culture medium and in solid agar, inoculated with Listeria monocytogenes. The best results were obtained in agar, exerting a bactericide effect, whereas in the liquid medium the coating had bacteriostatic behaviour. Furthermore, the active coating was applied to the surface of bags or separator liners made from polylactic acid. Its effectivity was evaluated with creamy mushroom soup (bags) and sliced cooked ham (separator liners) previously inoculated with L. monocytogenes and stored at 4 °C. Results showed that the coating was effective at inhibiting pathogen growth; however, it did not display a bactericide effect in the foods. In addition, L. lactis remained viable in all experiments conducted in this study. The acidification produced by L. lactis, because of the generation of organic acids, did not compromise the sensory properties of the sliced cooked ham after 16 days of refrigerated storage. In contrast, consumers perceived a mushroom soup acidification because of a greater decrease in pH than the sliced cooked ham. This study demonstrates that a food grade polyvinyl alcohol polymer blended with gelatin hydrolysates can be used as a carrier of protective cultures of L. lactis to increase the microbiological safety of refrigerated foods.

The authors acknowledge the financial support of the Ministerio de Ciencia e Innovación Español (AGL 2015-64595-R).

Peer reviewed