Novel composite films based on sodium alginate and carboxymethyl cellulose incorporated with lychee peel polyphenols: Physico-chemical properties, microstructure and food preservation

Lychee peels, rich in polyphenols, are typically discarded as fruit waste during processing. This study developed composite films incorporating lychee peel polyphenols (LPP) with sodium alginate and carboxymethyl cellulose to enhance preservation performance. The results showed that adding 2 mg/mL LPP increased the tensile strength of SA-CMC films by 153.0% (from 7.39 to 18.69 MPa), while higher LPP concentrations caused a significant decrease. As the LPP concentration increases, the UV transmittance and water vapor permeability of the composite film gradually decrease, while the static contact angle increases from 59.3° to 106.2°. FTIR and XRD analysis confirmed that LPP interacts with the film-forming matrix through non-covalent interactions. SEM showed that the film surface was smooth and uniform at low LPP concentrations (≤ 2 mg/mL), while high LPP concentrations resulted in slight wrinkling. Bananas and tomatoes were used to test the preservative properties of the film. Compared with the control group, the SCML-2 film effectively alleviated browning and weight loss (29.5% reduction) in the banana after 7 days of storage. However, when LPP ≥ 3 mg/mL, the preservation effect of the composite film was significantly reduced, even worse than that of the control group (tomato preservation experiment). A potential mechanism has been proposed to explain the interaction between LPP and the film-forming matrix. The findings establish that optimal LPP concentration requires balancing preservation efficacy with matrix compatibility, providing innovative insights into the use of LPP for the preparation of fresh fruit packaging films and the extension of food shelf life. • Integration of lychee peel polyphenols (LPP) into polysaccharide-based films • LPP enhancing mechanical strength (+60.15% at 2% LPP) and UV barriers of films • High LPP (≥3%) can lead to structural inhomogeneity and reduce functional properties • Films reduce banana browning and weight loss by 26–30% vs. control group