Nanoemulsions containing blends of essential oils in the control of Listeria innocua inoculated in mortadella

Abstract

Meat and its derivatives need special treatments in the handling and storage process because they are easily contaminated foods. Although these products meet market requirements, due to their great practicality, processed meat products are often contaminated by salt-resistant pathogenic microorganisms capable of multiplying during refrigerated storage. L. monocytogenes is a pathogen of interest in the food industry and has been highlighted in recent years in quality control due to the difficulties of elimination, as well as the possibility of causing serious diseases to consumers. This bacterium is involved in a large number of foodborne outbreaks around the world; and the foods most involved are ready-to-eat foods that are stored for long periods in refrigeration, especially meat products. Although this bacteria is eliminated by proper heat treatment of products, there is a possibility of contamination of the processing line when standard operating procedures fail. Currently, the quality, safety and authenticity of food are concerns of consumers who are increasingly looking for foods with a long shelf life and as natural as possible, so essential oils emerge as an alternative for replacement or combined use in reducing the use of synthetic preservatives in food. Due to the great instability of essential oils under environmental conditions, there are limitations in the use of these preservatives. This difficulty can be overcome by encapsulating these oils in nanoemulsions, which have better physicochemical characteristics and greater stability, in addition to increasing the biological activity of the oils due to their better distribution on certain surfaces. The aim of this study was to prepare mortadella with reduced concentration of nitrite, incorporating emulsions and nanoemulsions containing blends of essential oils, in order to evaluate the antimicrobial activity against Listeria innocua and the physicochemical and sensory characteristics of the meat product. Two combinations of essential oils were applied to the mortadella. In total, five different treatments were prepared: Control - without addition of essential oils; Treatment 1 - oregano essential oil (0.075325%), white thyme (0.07925%), chinese pepper (0.058675%) and clove leaf (0.07925%); Treatment 2 - oregano essential oil (0.0875%), white thyme (0.05%), chinese pepper (0.0875%) and clove leaf (0.15%); considering Treatments 1 and 2, two nanoemulsions were developed which constituted Treatments 3 and 4, respectively. The mortadella samples were stored at 8 °C for 21 days. The nanoemulsions were characterized for droplet size, polydispersity index and zeta potential. Technological characteristics of the samples, such as pH, lipid oxidation and color were analyzed. Sensory evaluation of mortadella was conducted by focus group. In general, the antimicrobial activity of treatments containing essential oils and nanoemulsions proved to be more efficient than the control treatment. Regarding the physicochemical analyses, there was no difference between the treatments for pH, lipid oxidation and color, however, an increase in lipid oxidation was observed along the storage time. Although the use of natural preservatives incorporated in mortadella formulations is interesting and attractive, changes in sensory characteristics must be considered. The present study presented a promising strategy to improve the safety of meat products, but more studies should be carried out to optimize the concentrations and types of essential oils, in order to reduce the impacts on sensory characteristics.