Purified Lotus Leaf Flavonoids in Lysozyme–Chitosan Coatings: Effects on Coating Properties and Strawberry Preservation

Conventional lysozyme–chitosan (LCS) coatings combine the film-forming properties of chitosan with lysozyme-mediated antibacterial activity, but their antioxidant capacity and activity against Gram-negative bacteria remain limited. In this study, purified lotus leaf flavonoids (LLF) were incorporated into a LCS matrix at 0.1–0.3% (w/v) to examine how a defined flavonoid fraction affects matrix structure, film performance, and strawberry preservation under ambient storage. LLF showed strong radical-scavenging activity, with IC50 values of 6.244 µg/mL for DPPH and 2.146 µg/mL for ABTS, and inhibited Staphylococcus aureus and Escherichia coli (MIC values of 0.625 and 1.25 mg/mL, respectively). Structural analyses indicated concentration-dependent, predominantly non-covalent interactions between LLF and the LCS network. LLF addition increased color intensity and opacity and altered water-related, barrier, thermal, and mechanical properties, revealing a formulation trade-off rather than uniform improvement of all material attributes. The LLF-LCS systems nevertheless showed stronger antioxidant and in vitro antibacterial activities than the CS and LCS controls. During 6 d of storage at 25 ± 2 °C, 0.2–0.3% LLF-LCS treatments reduced decay, limited weight loss, retained firmness, and better-preserved ascorbic acid, total phenolics, and anthocyanins. These findings demonstrate a formulation-dependent structure–property–preservation relationship for purified LLF in LCS coatings under short-term ambient storage and identify 0.2% LLF as the most balanced formulation within the tested range.