Limonene nanoemulsified with soya lecithin reduces the intensity of non-isothermal treatments for inactivation of Listeria monocytogenes

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.

Figure 1

Survivor curves obtained under isothermal conditions. Red dots indicate treatments without the addition of the nanoemulsified limonene. Samples with limonene are shown are blue triangles. The lines illustrate the model fits (dashed for samples with limonene, dotted for samples without). The facets represent different treatment temperatures (note the different scales in the x-axis).

Figure 2

Comparison between predictions based on isothermal data and survivor curves for dynamic treatments with a heating rate of (A) 1 °C/min, (B) 10 °C/min and (C) 20 °C/min. Red dots indicate treatments without the addition of the nanoemulsified limonene. Samples with limonene are shown are blue triangles. The ribbons represent the prediction intervals (95% confidence) based on isothermal experiments for control samples (red) and samples with nanoemulsified limonene (blue).