Valorization of Cincau Leaf and Red Ginger Waste-Derived Bioactives as a Sustainable Edible Coating for Postharvest Loss Reduction in Guava Fruit

Abstract

Guava (Psidium guajava L.) is highly perishable and loses vitamin C and market value rapidly after harvest, while most synthetic preservation methods raise food-safety and environmental concerns. Cincau (Premna oblongifolia) leaves and red ginger (Zingiber officinale var. rubrum), both underused local waste materials, offer a low-cost alternative for edible coatings, but their combined effect on guava has not been tested. This study formulated an edible coating from cincau leaf hydrogel and red ginger extract at several concentrations and evaluated its effect on the vitamin C content, antioxidant activity, and physical quality of guava during an 18-day storage trial. Coated and uncoated fruits were stored at room temperature and under refrigeration (8–10 °C); vitamin C was measured by iodometric titration, antioxidant activity by DPPH assay, and physical changes were recorded at three-day intervals. The formulation combining a high cincau concentration with a moderate red ginger concentration gave the best protection: after 18 days of refrigerated storage, coated fruit retained 65–70% of their initial vitamin C versus 35–40% in uncoated fruit, and antioxidant activity increased 1.5–2.0-fold relative to uncoated controls (p < 0.05). Coated guava also showed less browning, lower decay incidence, and slower softening. These results show that combining cincau hydrogel and red ginger extract creates a synergistic, biodegradable edible coating that can reduce postharvest losses and support circular-economy practices in tropical fruit supply chains.