Physical and functional characterization of whey protein-lignin biocomposite films for food packaging applications

Abstract

Whey protein isolate (WPI) and lignin are by-products of the cheese production and pulp and paper industries, respectively. The objective of this work was to analyze the physicochemical and mechanical properties of biodegradable films made from WPI (at different denaturation levels), glycerol, and lignin. WPI solutions were subjected to heat treatments at 60 °C, 90 °C, and a 1:1 mixture of 20 °C and 90 °C to induce varying levels of protein denaturation. Films produced at 90 °C, with 88.65 % protein denaturation, exhibited superior mechanical properties and lower water solubility compared to WPI films treated at lower temperatures. Adding lignin enhanced specific film properties: alkaline lignin increased glass transition temperature, opacity, UV blocking capacity, and antioxidant properties, while reducing flexibility. Conversely, lignosulfonate resulted in thicker films and improved UV shielding and antioxidant benefits. Microstructural analysis revealed that uneven lignin dispersion within the film matrix likely limited the overall lignin-induced enhancement of mechanical and barrier properties. These findings show that WPI-lignin films, especially those with optimized lignin dispersion, have potential as sustainable alternatives to conventional plastic packaging, providing improved UV protection, antioxidant properties, and mechanical strength. Further research is needed to enhance lignin integration techniques and assess the scalability of these films for industrial use.