Fat and fibre interfere with the dramatic effect that nanoemulsified d -limonene has on the heat resistance of Listeria monocytogenes

Abstract

The application of d-limonene in form of nanoemulsion has been proved to reduce dramatically the thermal resistance of Listeria monocytogenes in culture media. The present research shows very promising results on the application in food products. The thermal resistance of L. monocytogenes was reduced 90 times when 0.5 mM nanoemulsified d-limonene was added to apple juice. This is the biggest reduction in the heat resistance of a microorganism caused by an antimicrobial described ever. However, no effect was found in carrot juice. A carrot juice system was prepared in an attempt to unravel which juice constituents were responsible for the lack of effect. When fat and fibre were not included in the carrot juice system formulation, the thermal resistance of L. monocytogenes was, again, dramatically reduced in presence of nanoemulsified d-limonene, so these components were shown to interfere with the effect. Once this interaction with food constituents becomes solved, the addition of nanoemulsified antimicrobials would allow to reduce greatly the intensity of the thermal treatments currently applied in the food processing industry.

Nanoemulsified D-Limonene Reduces the Heat Resistance of Salmonella Senftenberg over 50 Times

“…This research expands the findings of the tremendous potential of nanoemulsified oily antimicrobials when combined with thermal treatments, formerly shown on L. monocytogenes [32,33], to Gram-negative bacteria, which are well known to show increased resistance to antimicrobials in comparison to Gram-positive bacteria. This result opens possible uses in the food industry.…”

“…As a consequence, the antimicrobial can reach the cell more easily. Maté et al [33] also found that the same effect was shown in a food product, such as apple juice. This finding was also very relevant, since most of the effect found with the combination of heat plus antimicrobials in culture medium is lost when they are applied in food products [34,36].…”

“…This finding was also very relevant, since most of the effect found with the combination of heat plus antimicrobials in culture medium is lost when they are applied in food products [34,36]. Even Maté et al [33] found that this dramatic effect could be almost completely lost depending on the composition of the food, showing that in carrot juice containing fat and fiber, the effect was lacking, but when these components were removed from the carrot juice, the effect was, again, dramatic.…”

“…Nanoemulsions have shown promising results when used to deliver antimicrobial compounds of essential oils, since nanoemulsified essential oil compounds show similar or even improved antimicrobial effects compared to the same substances added directly [14,22,29,30,31]. However, only Maté et al [32,33] have studied the synergistic effect of a mild heat treatment and an essential oil nanoemulsion. The synergistic effect led to a 100-fold reduction of the thermal resistance of L. monocytogenes both in culture medium [32] and in apple juice [33], which is by far the largest reduction in the heat resistance of a microorganism ever published when combining heat with natural antimicrobials.…”

“…However, only Maté et al [32,33] have studied the synergistic effect of a mild heat treatment and an essential oil nanoemulsion. The synergistic effect led to a 100-fold reduction of the thermal resistance of L. monocytogenes both in culture medium [32] and in apple juice [33], which is by far the largest reduction in the heat resistance of a microorganism ever published when combining heat with natural antimicrobials.…”