Sustainable chitosan and medicinal plant oils as natural edible coatings for postharvest quality preservation of guava fruits (Psidium guajava L.)

Postharvest loss of tropical fruits remains a significant challenge for food security and sustainability, as their delicate texture and high metabolic activity make them highly susceptible to rapid deterioration through handling and distribution. This study investigates the application of an edible coating technique to reduce loss, deterioration, and spoilage, and to increase the shelf-life of guava fruit. The fruits were immersed in chitosan and edible oils (moringa, lemongrass, marjoram, and rosemary). Chitosan (2%) and 1-2% moringa oil extended the shelf life of fruits by up to 24 days. Moringa oil at 1-2% mitigated the loss in fruit weight compared to 1% chitosan after the 24th day of storage, and the fruits had superior quality attributes (TSS, vitamin C, sugar content). The findings show that 2% chitosan and 1-2% moringa oil were the most effective treatments, reducing weight loss to about 10-25% compared to nearly 50% in untreated fruits and maintaining overall fruit quality. These treatments boosted peroxidase (POD) activity, reaching a peak of 76.47 U/g and keeping hydrogen peroxide (H2O2) levels low at 24.25 µmol g-¹ FW, signalling strong protection against oxidative stress. On the chemical side, they maintained higher total soluble solids (13.17 °Brix), total sugars (11.36%), and vitamin C (32.49 mg/100 mL), while keeping acidity lower (0.82%). By comparison, lemongrass and marjoram oil treatments were far less effective, showing faster weight loss and oxidative damage levels similar to those of the control group. Chitosan and oil coatings substantially reduce bacteria and yeasts/moulds on guava fruits, and moringa oil treatment improved physio-biochemical characteristics and reduced postharvest disease spoilage. The results highlight that natural coatings, particularly chitosan and moringa oil, not only preserved the physio-biochemical quality of guava but also offered a sustainable, biodegradable solution that can help reduce food loss, limit reliance on synthetic chemicals, and support environmentally responsible postharvest management practices.