Influence of partial inactivation on growth of Listeria monocytogenes under sub-optimal conditions of increased NaCl concentration or increased acidity

The effect of partial inactivation with lactic acid (LA), liquid chlorine dioxide (ClO₂) and intense light pulses (ILP) on injury and post-treatment growth under increased NaCl concentration and reduced pH values of Listeria monocytogenes strains was investigated. Inactivation levels and the percentage of sub-lethal were dependent upon strain and type of inactivation technique used. Comparison of the mean time-to-detection (TTD) values under suboptimal conditions (increased NaCl concentration or reduced pH) showed that the longest TTD was at every pH observed for the cultures treated with ClO₂, followed by LA and ILP. Under increased NaCl concentration LA treated cells required the longest TTD, followed by ClO₂ and ILP, respectively. Significant difference in TTD between untreated and cultures treated with ClO₂ and LA was observed. Recovery of ILP treated cultures was not always different from untreated cultures. The extended post-treatment effect based on the growth retardation or inhibition of injured cells under sub-optimal conditions is suggested as an important tool in conditioning of microbial food safety.Industrial relevanceSmall and medium sized enterprises (SMEs) are the backbone of the European economy. They are a key source of jobs and a breeding ground for implementation of research results. They are however the most sensitive of all to changes in the production practices coming as a consequence of increased consumers' awareness regarding fresh and natural-like foods. In order to respond to the changed consumption pattern, non-heat and so-called mild technologies have emerged. This research as a part of the EU Pathogen Combat project is tailor made to answer some of the burning issues when it comes to “mild” decontamination. Among the more established technologies used here is decontamination with lactic acid, followed by chlorine dioxide. Both are now under the eye of EU policy makers who are seeking relevant facts to adjust or not to adjust EU policy regarding decontamination of foods. Latest EFSA opinions have already pushed these agents forward, but relevant scientific facts were declared missing. Moreover, intense light pulses, as non-chemical alternative to pasteurization have a considerable potential not only in food surface decontamination, but also in the decontamination of packaging materials, industrial surfaces etc. The present research brought new facts into the light that might have a credible influence on understanding pros and cons of lactic acid, chlorine dioxide and intense light pulses as decontamination agents. The post-treatment, based on sublethal injury, effect is suggested as an important extension tool in shelf life extension and safety barrier.