Pomelo Peel Flavonoids: From Extraction and Microencapsulation to Dosage-Dependent Modulation of Starch/KGM Composite Film Properties

In this study, pomelo peel waste was utilized as the raw material to extract flavonoids, which were subsequently microencapsulated with β-cyclodextrin (β-CD) and incorporated into a corn starch/konjac glucomannan composite film matrix, aiming to develop biodegradable candidate films containing an antioxidant extract for potential food packaging applications. The extraction conditions for pomelo peel flavonoids (PF) were optimized via response surface methodology, yielding the optimal parameters as follows: extraction time of 123.88 min, temperature of 69.07 °C, etc., under which the total PF extraction rate reached 5.958%. At high concentrations, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacities of the obtained PF did not differ significantly from those of ascorbic acid. The fabricated PF-loaded β-cyclodextrin microcapsules (PF-CD-MCs) achieved an encapsulation efficiency of 71.24 ± 0.21%, the morphological and spectroscopic results suggested the successful formation of the inclusion complex and were incorporated into the composite films at varying addition levels ranging from 0% to 40% (w/w). The results demonstrated that the loading content of PF-CD-MCs played a critical regulatory role in the microstructure and macroscopic properties of the films. At 10% loading, the water vapor permeability (WVP) reached its minimum, whereas 20% loading provided the best overall compromise: the microcapsules remained uniformly dispersed without recrystallization, the film retained acceptable barrier and mechanical performance, and the active loading was higher than that at 10%. At 30%–40%, aggregation and recrystallization caused structural defects and marked deterioration in WVP, mechanical strength, and water resistance. Therefore, 20% is recommended as a comprehensive loading level rather than a single-property optimum. This study provides important theoretical foundations and technical references for the high-value utilization of pomelo peel waste and the rational design of biodegradable active packaging materials.