Incorporation of mangosteen peel powder into starch-based films: Structure-property-function relationships and bioactivity.

Starch-based films are promising candidates for sustainable packaging applications, but their practical use is often limited by insufficient mechanical strength, poor moisture resistance, and restricted functionality. In this study, mangosteen peel powder (MPP), an agro-industrial by-product rich in naturally occurring bioactive compounds, was directly incorporated into starch-based films as a multifunctional filler. The effects of MPP loading and particle size on film structure and performance were systematically investigated. MPP incorporation influenced particle dispersion and interfacial characteristics within the starch matrix, which in turn affected the mechanical, moisture-related, optical, and bioactive properties of the films. Among the formulations studied, the 4% MPP film exhibited the best overall performance, with a tensile strength of 32.5 MPa, water absorption of 5.71 g/g, and DPPH radical scavenging activity of 83.7%. In addition, MPP incorporation significantly improved UV-shielding performance, reducing transmittance at 300 nm from 83.1% for the pure starch film to 5.0-8.0% for MPP-containing films. Although higher MPP loading (6%) enhanced bioactivity, it led to reduced mechanical and moisture barrier performance due to aggregation effects. Overall, MPP acts as an effective multifunctional modifier for starch-based films, providing a sustainable strategy for developing bioactive and biodegradable packaging materials.