Preparation of carboxymethyl chitosan/polyvinyl alcohol double-layer film loaded with tannic acid- zeolitic imidazolate framework-8@quercetin particles for lotus root preservation.

Abstract

Rapid release of active compounds from packaging films reduces preservation efficacy, significantly diminishes antioxidant and antibacterial effects. Zeolitic imidazolate framework-8 (ZIF-8) exhibited increased porosity after tannic acid (TA) etching. This facilitated sustained drug release and enhanced the material's sensitivity to acidic environments. By optimizing the size of ZIF-8, the etching content of TA, and the loading of quercetin (Qe), a composite material of TA-ZIF-8@Qe was synthesized. The double-layer film was fabricated using a layer-by-layer solution-casting method, comprising a carboxymethyl chitosan layer with varying concentrations of TA-ZIF-8@Qe and a polyvinyl alcohol layer. Incorporation of TA-ZIF-8@Qe improved the film's tensile strength as well as its antioxidant and antimicrobial activities. The film exhibited biological safety and biodegradability, without affecting seed growth. At a loading capacity of 12%, the cumulative release rates of the film over 96 h were 47.55%, 56.88%, and 63.65% at pH levels of 6.77, 5.50, and 4.65, respectively. After 12 days of storage under the same double-layer film conditions, films stored at 25 °C exhibited lower water-vapor permeability but higher oxygen permeability than those stored at 4 °C. At the same temperature, compared to the carboxymethyl chitosan layer, the water vapor and oxygen permeability of the polyvinyl alcohol layer as the outer layer was lower. The optimized film extended the shelf life of lotus root slices to 12 days under refrigeration at 4 °C and to 8 days at 25 °C. This study highlights the significant potential of this double-layer film as a food packaging material.