Enhancement of Antioxidant Activity and Inhibition of Polyphenol Oxidase from Green Oak Lettuce by Chitosan-Encapsulated Rambutan (Nephelium lappaceum L.) Peel Extract

Enzymatic browning in fresh-cut lettuce remains a critical challenge in the food industry, driving the search for effecti ve natural preservatives. This study explores the innovative encapsulation of rambutan (Nephelium lappaceum L.) peel bioactive compounds with chitosan to enhance their stability and bioactivity. Among the various rambutan peel extracts (RPE) evaluated, the methanolic extract exhibited the highest DPPH scavenging acti vity (IC50: 2.28 ± 0.15 μg/mL), correlated with its total phenolic content. The ethanolic extract also demonstrated strong antioxidant activity (IC50: 3.26 ± 0.17 μg/mL) and was selected for further studies due to its balanced antioxidant performance and suitability as a food-grade solvent for potential commercial applications. Liquid chromatography-mass spectrometry (LC-MS) analysis identified Sanguiin H11 and ellagic acid as the key phenolic compounds. Notably, ellagic acid demonstrated strong molecular docking with polyphenol oxidase (PPO), showing a binding energy of -6.75 kcal/mol through specific hydrogen bonding through indicated that ellagic acid has a superior binding affinity compared to the reference inhibitor tropolone (-5.20 kcal/mol). The optimized chitosan encapsulation system (10:1 w/w RPE: chitosan ratio) produced uniform spherical microcapsules (3403 ± 8.79 nm) with excellent colloidal stability (zeta potential: 31.17 ± 0.83 mV) and high encapsulation efficiency (60.53 ± 0.48%). This formulation significantly enhanced both DPPH radical scavenging activity (6.99-fold increase) and green oak lettuce polyphenol oxidase (goPPO) inhibition (2.29-fold improvement) compared to the chitosan control group. This research demonstrated the successful conversion of agricultural waste into effective natural preservatives with PPO inhibitory and antioxidant activities, offering a promising solution for fresh-cut produce preservation.