Oregano essential oil-pectin edible films as anti-quorum sensing and food antimicrobial agents.

Edible films can be used as carriers for antimicrobial compounds to assure food safety and quality; in addition, pathogenesis of food bacteria is related to a cell to cell communication mechanism called quorum sensing (QS). Oregano essential oil (OEO) has proved to be useful as food antimicrobial; however, its food applications can be compromised by the volatile character of its active constituents. Therefore, formulation of edible films containing OEO can be an alternative to improve its food usages. QS inhibitory activity of OEO and pectin-OEO films was evaluated using Chromobacterium violaceum as bacterial model. Additionally, antibacterial activity was tested against Escherichia coli O157:H7, Salmonella Choleraesuis, Staphylococcus aureus, and Listeria monocytogenes. OEO was effective to inhibit bacterial growth at MIC of 0.24 mg/mL for all tested bacteria and MBC of 0.24, 0.24, 0.48, and 0.24 mg/mL against E. coli O157:H7, S. Choleraesuis, S. aureus, and L. monocytogenes, respectively. Pectin-films incorporated with 36.1 and 25.9 mg/mL of OEO showed inhibition diameters of 16.3 and 15.2 mm for E. coli O157:H7; 18.1 and 24.2 mm for S. Choleraesuis; 20.8 and 20.3 mm for S. aureus; 21.3 and 19.3 mm for L. monocytogenes, respectively. Pectin-OEO film (15.7 mg/mL) was effective against E. coli O157:H7 (9.3 mm), S. aureus (9.7 mm), and L. monocytogenes (9.2 mm), but not for S. Choleraesuis. All concentrations of OEO (0.0156, 0.0312, 0.0625 and 0.125 mg/mL) and pectin-OEO films (15.7, 25.9 and 36.1 mg/mL) showed a significant anti-QS activity expressed as inhibition of violacein production by C. violaceum. Additionally, the application of pectin-OEO films was effective reducing total coliforms, yeast, and molds of shrimp and cucumber slices stored at 4°C during 15 d. These results demonstrated the potential of pectin films enriched with OEO as food related microorganisms and QS inhibitors.

Essential oils as biopreservatives: different methods for the technological application in lettuce leaves.

Investigations were carried out to assess the efficiency of 3 essential oils, clove, tea tree, and rosemary, as natural preservatives during the postharvest of lettuce leaves. The effect of different concentration (1 and 0.5 MIC) of plant essential oils applied in 3 forms (spray, immersion, and capsules) was studied on lettuce leaves. The evolution of different microbial populations was evaluated during refrigerated storage. The application forms of the biopreservatives were shown to be an important factor in determining the effectiveness of the essential oils. Clove and tea tree essential oils at 1 MIC and applied embedded in lactose capsules presented a significant inhibition on mesophilic, psicrotrophic, and coliforms populations, while rosemary in none of the 3 technological applications forms exerted inhibitory effect on all microbial populations evaluated. Essential oils (at 0.5 MIC) applied by spray, immersion, and embedded in lactose capsules exerted lower inhibitory effects, with respect to 1 MIC, on the different microbial populations present on lettuce leaves. At the end of the storage (7 d), lettuce samples treated with tea tree, clove, and rosemary (at 1 and 0.5 MIC) by spray were the only organoleptically acceptable. It is concluded that clove and tea tree essential oils can control different microbial population present in lettuce. Practical Application: The exploration of naturally occurring antimicrobials in food preservation receives increasing attention due to consumer awareness of natural food products. Biopreservatives are useful in extending the shelf life of foods, reducing or eliminating pathogenic bacteria and increasing overall quality of food products. The effectiveness of essential oil application in foods is the result of factor associations such as applications forms, concentration applied, the way of action, storage temperatures. The application methods (spray, immersion, and embedded in lactose capsules) and the concentration of essential oils have been shown to be important factors in determining the effectiveness of these biopreservatives. The oil concentrations required to produce a certain level of inhibition in actual foods could be questionable due to the organoleptic impact. However, these novel natural preservatives in combination with other factors in obstacle technologies are an alternative to control the pathogen growth minimizing undesirable changes in organoleptic characteristics.

Effectiveness of edible coatings combined with mild heat shocks on microbial spoilage and sensory quality of fresh cut broccoli (Brassica oleracea L.).

UNLABELLED: The use of edible coatings and mild heat shocks is proposed as postharvest treatments to prevent microbial deterioration of refrigerated broccoli. Minimally processed broccoli was coated with either chitosan or carboxymethyl-cellulose (CMC) combined or not with a previous application of a mild heat shock. The evolution of microbial populations (mesophilic, psycrotrophic, Enterobacteriaceae, molds and yeast, and lactic acid bacteria) was studied during 20 d of storage and fitted to Gompertz and logistic models. Results revealed that, at the end of the storage, chitosan coating significantly reduced all microbiological population counts, except lactic acid bacteria; while higher reduction was observed with chitosan coating combined with a heat shock treatment. A significant delay at the beginning of the exponential phase was observed for all the bacterial populations analyzed. On the other hand, CMC coating, with and without a previous thermal treatment, did not exert any antibacterial effect. Excellent agreement was found between experimental microbial counts and predicted values obtained from Gompertz and logistic models. Kinetic modeling was found to be valuable for prediction of microbiological shelf life of broccoli during storage. Results showed that the application of chitosan coating effectively maintained microbiological quality and extended shelf life of minimally processed broccoli. According to these results, the use of the edible chitosan coating alone or in combination with a heat mild shock appear to be a viable alternative for controlling microbiological growth and sensory attributes in minimally processed broccoli. PRACTICAL APPLICATION: The continuous consumer interest in high quality and food safety, combined with environmental concern has induced to the development and study of edible coatings that avoid the use of synthetic materials. The edible coatings, formed from generally recognized as safe materials, have the potential to reduce weight loss, respiration rate, and improve food appearance and integrity. It is one of the most effective methods to maintain food quality. On the other hand, heat treatments have been demonstrated to be effective as a nonchemical means of improving postharvest quality for a variety of horticultural products. The applications of mild heat shocks combined with edible coatings constitute an alternative for the natural preservation of crops for which the use of synthetic chemicals is objectionable.