Essential oils of thyme and Rosemary in the control of Listeria monocytogenes in raw beef

Abstract

This study was developed in order to evaluate two alternatives for the control of Listeria monocytogenes in raw bovine meat pieces, both based on the use of Thymus vulgaris and Rosmarinus officinalis essential oils (EOs). The antilisterial activity of different concentrations of the EOs was tested in vitro using agar dilution and disk volatilization techniques. In addition, L. monocytogenes was inoculated in meat pieces, which were submerged in edible gelatin coatings containing 2% (v/v) EOs or submitted to the vapor of EOs (0.74 μL.cm(-3)). L. monocytogenes was quantified after one, 48 and 96 hours of storage (7 °C). In the in vitro tests, the EO of T. vulgaris presented higher activity. The two options used (edible gelatin coating and vapor activity), in spite of exercising effects with differentiated behaviors, presented antibacterial activity against L. monocytogenes inoculated in raw bovine meat (p < 0.05). Greatest antibacterial activity were obtained in the experiment that used edible coatings containing EOs, at 48 hours of storage reductions in bacterial counts between 1.09 and 1.25 Log CFU.g(-1) were obtained. In the vapor effect experiment, the EO of T. vulgaris caused the highest reduction in the population of bacteria inoculated in raw bovine meat (p < 0.05), 0.40 Log CFU.g(-1) at 96 hours of storage. This study supplied important information regarding new and promising natural alternatives, based on the concept of active packaging, for the control of L. monocytogenes in the meat industry.

Keywords: Rosmarinus officinalis; Thymus vulgaris; active packaging; antilisterial compounds; meat safety.

Figure 1

Main stages of the experiment that evaluated the antibacterial activity of edible gelatin coatings containing essential oils (EOs) of Thymus vulgaris and Rosmarinus officinalis against Listeria monocytogenes inoculated in raw beef pieces. (A) L. monocytogenes inoculation in raw beef pieces. (B) Drying of the raw beef pieces after the bacterial inoculation step. (C) Recipients containing the edible coating solutions of gelatin, from left to right: solution without the addition of EOs, solution containing T. vulgaris EO, solution containing R. officinalis EO. (D) Drying of the raw beef pieces after the edible coating application. (E) Raw beef piece with the application of edible gelatin coating containing T. vulgaris EO inside a polyethylene terephthalate packaging, after 1 hour storage at 7 °C.

Figure 2

Effect of the Thymus vulgaris essential oil vapor on the formation of Listeria monocytogenes inhibition zones on the culture medium surface after incubation at 37 °C for 24 hours.