Essential Oils and Bacteriocin-Based Active Edible Coating: An Innovative, Natural and Sustainable Approach for the Control of Listeria monocytogenes in Seafoods

The anti-Listeria monocytogenes activity of four essential oils (EOs) (Salvia officinalis, Citrus limon, Mentha piperita and Thymus vulgaris) and bacteriocin bacLP17, added alone or in mixture in active edible coatings, was determined in artificially contaminated shrimps. The minimal inhibitory concentration (MIC) values of the EOs were determined against the NCTC 10888 strain of L. monocytogenes by using the broth microdilution method. The checkerboard method was carried out in tryptic soy broth (TSB), using microdilution to obtain the Fractional Inhibitory Concentration Index (FIC-Index) for six associations of EOs, chosen based on the best MIC results. All the EOs confirmed their anti-Listeria activity, both “in vitro” and inside the coatings. The coating matrix was suitable for use in the food field, allowing a gradual release of the EOs in packaged food. When the EOs were used in association (EO/EO) they were demonstrated to act synergistically, leading to a significant reduction in the amount (10–20 times) of EOs needing to be used, and consequently a decrease in the strong smell on the food. This effect was also confirmed when the compounds were incorporated into the coatings. The inclusion of the EOs within the coating not only ensured the anti-Listeria activity by increasing the shelf-life of food products, but also further mitigated the strong smell of the EOs, improving the organoleptic impact on the food and its sensory properties. Keywords: Listeria monocytogenes; shrimp; essential oils; bacteriocin; edible coating

Eco-Friendly Edible Packaging Systems Based on Live-Lactobacillus kefiri MM5 for the Control of Listeria monocytogenes in Fresh Vegetables

To meet consumer requirements for high quality food free of chemical additives, according to the principles of sustainability and respect for the environment, new “green” packaging solutions have been explored. The antibacterial activity of edible bioactive films and coatings, based on biomolecules from processing by-products and biomasses, added with the bacteriocin producer Lactobacillus kefiri MM5, has been determined in vegetables against L. monocytogenes NCTC 10888 (i) “in vitro” by a modified agar diffusion assay and (ii) “on food” during storage of artificially contaminated raw vegetable samples, after application of active films and coatings. Both polysaccharides-based and proteins-based films and coatings showed excellent antilisterial activity, especially at 10 and 20 days. Protein-based films displayed a strong activity against L. monocytogenes in carrots and zucchini samples (p < 0.0001). After 10 days, both polysaccharide-based and protein-based films demonstrated more enhanced activity than coatings towards the pathogen. These edible active packagings containing live probiotics can be used both to preserve the safety of fresh vegetables and to deliver a beneficial probiotic bacterial strain. The edible ingredients used for the formulation of both films and coatings are easily available, at low cost and environmental impact

Improving diced tomato firmness by pulsed vacuum calcification

Vacuum impregnation is a non-thermal technique used in food technology to replace the air occluded in the products with specific substances, thus modifying food quality. Here, this technique was employed to allow calcium ions to penetrate more efficiently in the tissue structure of diced tomatoes with consequent increase of the product firmness. Calcification was obtained in two ways, that is, either by keeping diced tomatoes at the reduced pressure of 100 mbar or by subjecting the product to cycles of pulsed vacuum from 1013 mbar to 30 mbar. Both procedures were conducted in the presence of calcium chloride solutions at various concentrations and temperatures. The results showed that the highest firmness was obtained by pulsed vacuum calcification at 30 mbar and 45 °C by using 4 cycles of pulsed vacuum. In these conditions, after two-months storage at room temperature, the treated diced tomatoes packaged in tinplate cans showed firmness increase of about 90% with respect to product not treated by vacuum infiltration. These results indicate the pulsed vacuum calcification as a promising process that can be effectively introduced in some phases of the industrial tomato transformation to improve the product texture

Improving diced tomato firmness by pulsed vacuum calcification

Vacuum impregnation is a non-thermal technique used in food technology to replace the air occluded in the products with specific substances, thus modifying food quality. Here, this technique was employed to allow calcium ions to penetrate more efficiently in the tissue structure of diced tomatoes with consequent increase of the product firmness. Calcification was obtained in two ways, that is, either by keeping diced tomatoes at the reduced pressure of 100 mbar or by subjecting the product to cycles of pulsed vacuum from 1013 mbar to 30 mbar. Both procedures were conducted in the presence of calcium chloride solutions at various concentrations and temperatures. The results showed that the highest firmness was obtained by pulsed vacuum calcification at 30 mbar and 45 °C by using 4 cycles of pulsed vacuum. In these conditions, after two-months storage at room temperature, the treated diced tomatoes packaged in tinplate cans showed firmness increase of about 90% with respect to product not treated by vacuum infiltration. These results indicate the pulsed vacuum calcification as a promising process that can be effectively introduced in some phases of the industrial tomato transformation to improve the product texture