Layer-by-Layer Electrostatic Deposition of Edible Coating on Fresh Cut Melon Model: Anticipated and Unexpected Effects of Alginate–Chitosan Combination

Edible coatings attract interest today as efficient and safe techniques for controlling the deterioration and extending the shelf-life of food products. In the present study, a layer-by-layer (LbL) electrostatic deposition of oppositely charged natural polysaccharides, a polyanion alginate and a polycation chitosan, was implemented for coating a model food: fresh-cut melon. The performance of the alginate–chitosan coating was compared with single-layer coatings and with non-coated control. The LbL coating was found to possess the beneficial properties of both ingredients, combining good adhesion to melon matrix of the inner alginate layer with antimicrobial activity of the outer chitosan layer, thereby reducing the bacteria, yeast, and fungi counts by 1–2 log CFU. The bilayer coating slowed down tissue texture degradation, so that after 14 days of storage only LbL samples maintained an appreciable firmness. An unexpected benefit of the LbL coating was that its enhanced gas-exchange properties exceeded those of both monolayer coatings and even of the non-coated control. As a result, the LbL coating prevented an increase in headspace CO₂ and ethanol concentrations, which are the signs of hypoxic stress and off-flavor development observed in other samples, especially in alginate-coated melons. The phenomenon was presumably related to swelling behavior of the chitosan layer in the humid atmosphere of the fresh-cut melon package, giving the melon pieces an attractive succulent appearance. At the same time, the LbL coating resulted in somewhat increased produce weight loss due to the reduced surface water vapor resistance. The method is cheap, simple, and can improve the quality and safety of food products.