Postharvest Quality Preservation and Shelf-Life Extension of Apples Through Edible Coatings and Natural Preservative Treatments

Abstract

Apples (Malus domestica), a leading temperate fruit crop valued for their nutritional and sensory qualities, experience substantial postharvest losses (8.6–50%) driven by rapid climacteric respiration, ethylene biosynthesis via the Yang cycle, transpiration-induced weight loss, enzymatic browning mediated by polyphenol oxidase (PPO), and microbial decay (primarily anthracnose and stem-end rot). Edible coatings formulated from polysaccharides (chitosan, starch, alginate, pectin), proteins (whey protein, zein), lipids (carnauba wax, beeswax), and composite blends create a semi-permeable barrier that modulates internal atmosphere, reduces O₂ availability and CO₂ accumulation, slows ethylene production and respiration, limits moisture loss, delays cell-wall degradation by polygalacturonase and pectin methylesterase, and inhibits enzymatic browning and pathogen growth. Incorporation of natural bioactive agents’ essential oils (cinnamon, oregano), nisin, lysozyme, ascorbic acid, and citric acid transform these coatings into active packaging systems with enhanced antimicrobial and antioxidant properties. Advanced application technologies, including electrostatic spraying, electrospraying, and nano-emulsions, improve uniformity, adhesion, and controlled release. Research demonstrates significant shelf-life extension (up to 21 days), retention of firmness, titratable acidity, ascorbic acid, total phenolics, and visual appeal, while reducing weight loss, browning index, and decay incidence. This review underscores edible coatings as a sustainable, consumer-friendly alternative to synthetic fungicides and plastic packaging, offering a practical solution to minimize postharvest waste, enhance market value, and support circular-economy principles in the global apple industry.