Abstract
Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. This type of products have minimal processing conditions that can enable the survival and replication of pathogenic microorganisms. Among them, Listeria monocytogenes is of special concern, due to its relatively high mortality rate and its ability to replicate under refrigeration conditions. Previous research works have shown that nanoemulsified essential oils in combination with thermal treatments are effective for inactivating L. monocytogenes. However, previous research works were limited to isothermal conditions, whereas actual processing conditions in industry are dynamic. Under dynamic conditions, microorganism can respond unexpectedly to the thermal stress (e.g. adaptation, acclimation or increased sensitivity). In this work, we assess the combination of nanoemulsified D-limonene with thermal treatments under isothermal and dynamic conditions. The nanoemulsion was prepared following an innovative methodology using soya lecithin, a natural compound as well as the essential oil. Under isothermal heating conditions, the addition of the antimicrobial enables a reduction of the treatment time by a factor of 25. For time-varying treatments, dynamic effects were relevant. Treatments with a high heating rate (20 °C/min) are more effective than those with a slow heating rate (1 °C/min). This investigation demonstrates that the addition of nanoemulsified D-limonene can greatly reduce the intensity of the thermal treatments currently applied in the food industry. Hence, it can improve the product quality without impacting its safety.
Highlights
Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years
The aim of this study is to evaluate the combined effect of a thermal treatment with a nanoemulsion of D-limonene, using an innovative emulsification technique based on soya lecithin, on the inactivation of L. monocytogenes
The addition of the natural antimicrobial to the heating medium has a dramatic impact on the resistance of the L. monocytogenes cells to the treatment
Summary
Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. Previous research works have shown that nanoemulsified essential oils in combination with thermal treatments are effective for inactivating L. monocytogenes. There are still several technological challenges that limit the application of natural antimicrobials in food industries They are susceptible to oxidative degradation (which greatly reduces their effect) and they have a pronounced aromatic character that can impact the flavor of the food product. The synergistic effect led to a 100-fold reduction of the thermal resistance of L. monocytogenes both in culture medium[26] and in apple juice[25], and a 50-fold reduction of the thermal resistance of Salmonella Senftenberg[27], which are, by far, the largest reductions in microbial heat resistance ever published when combining heat with natural antimicrobials These studies were limited to the application of isothermal treatments (constant temperature), whereas in the ones applied in industry the temperature is dynamic. We have performed experiments under isothermal and dynamic heating conditions to assess the interaction between the dynamics of the temperature and the effect of the nanoemulsified natural antimicrobial
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