Efficient biosynthesis of levan using recombinant levansucrase and preservation efficacy of edible composite films

Levan is a biodegradable and biocompatible microbial polysaccharide with promising food and biomedical applications. However, the low soluble expression of levansucrase (SacB) severely hinders large-scale levan production. This study aimed to enhance SacB expression and explore levan-based functional edible films for fruit preservation.

A VNp6 signal peptide-fused recombinant expression system coupled with bacterial envelope material (BEM) particle immobilization was constructed to realize efficient SacB expression and streamline enzyme purification. Bioinformatic and enzymatic assays verified that the recombinant SacB was a structurally stable soluble protein. The enzyme exhibited optimal catalytic activity at pH 5.8 and 50 °C, affording a levan yield of 21.18 g L^-1 under optimized conditions. Structural characterization demonstrated that the enzymatically synthesized levan possessed a porous β-(2 → 6)-linked network structure suitable for edible film fabrication. Levan-based composite films with 2 g kg^-1 tea polyphenols exhibited integrated desirable properties, including strong antioxidant activity, broad-spectrum antibacterial ability and favorable mechanical performance, which effectively alleviated fruit spoilage and displayed great potential for berry preservation.

This study established an integrated technical system for SacB expression and levan functional utilization. It provides a novel strategy for high-efficiency heterologous SacB expression and offers theoretical and technical support for developing green packaging materials and high-value levan application. © 2026 Society of Chemical Industry.