Essential oils as natural antimicrobials for application in edible coatings for minimally processed apple and melon: A review on antimicrobial activity and characteristics of food models

Essential oils (EOs) present a strong in vitro antimicrobial activity against pathogenic bacteria and fungi, acting mainly by permeabilization of the cellular membrane. Synergism between active compounds of EOs, especially those rich in phenolic terpenoids is an important attribute of EOs that makes them suitable for application as food-grade natural additives. In this context, EOs incorporation into edible coatings (ECs) for minimally processed (MP) apples and melons was reviewed. EOs inclusion at doses between 0.05% and 3% in ECs resulted in an additional inhibitory effect on the endogenous microflora (mesophiles, psychrophiles, psychrotrophs, yeasts and molds) as well on inoculated pathogen strains on coated fruits throughout storage, especially at doses higher than 0.5%. Low EO doses can act synergistically with antibrownings like organic acids, and with texture enhancers depending on the coating material used. EOs helped to maintain pulp firmness adding a hydrophobic barrier to ECs thus reducing weight loss of fruits. However, at doses higher than 0.3%, EOs were likely to trigger browning reactions, regardless of the presence of antioxidants, and their volatilization also caused changes to the fruits' aroma and flavor lowering sensory scores. Novel approaches include encapsulating EOs within nanoscale polymers as cyclodextrins, developing multilayer coatings and nanoemulsions, providing a controlled and sustained EO release through EC matrix that can mask EOs' aroma. Applying mild doses of EOs in ECs is an effective combined approach to inhibit microbial growth, avoid physical and sensory changes, and extend the shelf life of refrigerated MP fruits in several days.