Evaluation of natural compounds against Listeria innocua: Translating in vitro success to processed meat models

Ensuring food safety is a significant challenge in the processed meat industry. Listeria monocytogenes represents a persistent threat due to its ability to grow in adverse conditions. Nowadays, there's a growing interest in natural preservatives to inhibit its proliferation in foods. Accordingly, the aim of the present study was to preliminarily evaluate the in vitro inhibitory activity of various natural antimicrobial agents against Listeria innocua, used as a surrogate for L. monocytogenes. Thyme essential oil (EO) emerged as the most effective candidate for further in vivo testing in pork minced meat with 40% fat and no additional fat, deliberately contaminated with L. innocua. The samples were stored for 20 days under two different temperature conditions, mimicking common procedures used to produce salami with short ripening periods and high fat content, such as the Italian Ciauscolo PGI salami, either through spontaneous fermentation or with the use of starter cultures. In vivo, the inhibitory effect of thyme EO was minimal or absent, regardless of fat content. Statistically significant decreases in L. innocua counts (<2%) were sporadic and observed solely in samples stored under temperature conditions mimicking the typical procedure for spontaneously fermented salami production. However, this effect was not sustained until the end of the experiment. While thyme EO demonstrated potential as an antilisterial agent in vitro, our findings highlight the complex interaction between antimicrobial agents and food matrices, revealing challenges in practical applications. This underscores the importance of further investigation elucidating the effectiveness of antimicrobial agents in real food systems.