Application of chitosan enriched with essential oils to protect fresh foodstuffs from the attack of dipteran pests.

Each year, from 12 to 20% of worldwide food production is lost during post-harvest and post-production stages due to biotic factors, including several insect pest species. Fruit flies pose a threat to both the yield in the field and the handling and retailing of fruits, while blowflies and cheese skippers are dangerous to meat and ripening cheese products in places where hygienic conditions are scarce and in the event of failures along the cold chain network. From a food sustainability perspective, this work aimed to evaluate the protection given by essential oils (EOs) and chitosan against the oviposition of fresh foodstuff dipteran pests, specifically, Ceratitis capitata (Tephritidae) on kumquat fruits (Citrus japonica, Rutaceae), Drosophila suzukii (Drosophilidae) on blueberries (Vaccinium myrtillus, Ericaceae), Calliphora vomitoria (Calliphoridae) on raw beef meat, and Piophila casei (Piophilidae) on cheese and hams during curing. EOs raise great interest as an eco-friendly alternative with low toxicity to synthetic repellents and insecticides, although, currently, their actual use in food protection is limited due to their high volatility and the potential alteration of foodstuffs’ organoleptic qualities. Chitosan, a renewable and biodegradable polysaccharide already known as a preservative in the food industry, is proposed here as a stabiliser for the volatile component of EOs to prolong and/or enhance their bioactivity. Through oviposition deterrence trials specifically adapted to the four dipteran species, we tested and compared, under laboratory conditions, the protective action of some EOs (concentrations from 0.5 to 2.0% in ethanol), chitosan solutions (from 0.5 to 2.0% w/v in aqueous solution), and chitosan formulations enriched with the correspondent EOs (same chitosan concentration and EO content). The EOs were selected by a trained panel of sensory judges who found the best combinations with the different foodstuffs and were then chemically characterised through GC-EIMS. For kumquat fruits and blueberries, the chosen EOs were Cinnamomum verum (Lauraceae, main component (E)-cinnamaldehyde 58.7%) and Citrus reticulata (Rutaceace, limonene 83.6%); for meat products and cheese, they were Laurus nobilis (Lauraceae, 1,8-cineole 28.1%) and Piper nigrum (Piperaceae, β-caryophyllene 45.7%). All treatments produced a significant reduction in oviposition compared to the untreated control samples, with a prolonged protective action over time from the EOs-enriched chitosan solutions. The results of the trials will be discussed based on the different biology and oviposition behaviour of the four dipteran species, the potential repellent or attractive effect of the employed EOs, and the possible practical applications of the chitosan formulations enriched with EOs in fresh foodstuffs protection.