PRODUCING PROTEIN FILMS WITH BIOBASED ADDITIVES AS A SUSTAINABLE PLASTIC PACKAGING ALTERNATIVE

Abstract

As an alternative to traditional plastic food packaging, interest has increased in biopolymers because they are more sustainable than conventional plastics. For example, plant-based proteins can be sourced from various waste streams and have the innate ability to form films projected to be home-compostable. Plasticizer and solvent choice are important when casting films to reduce brittleness and improve film tenacity through cross- linking. Glycerol, the most used bio-plasticizer, is prone to migrate out of films, thus reducing the films’ flexibility and shelf life. Our study aimed to couple the plasticizing effects of phenolic compounds with the protein solubilizing properties of formic acid to enhance protein film integrity. Films were solution-cast by dissolving plant proteins (gluten, zein, or soy) in combination with polyphenol extracts (green tea extract and grape seed extracts with low or high proanthocyanidin content – 26 or 48%, respectively) and

glycerol at different concentrations (10% or 20% w/w protein) in formic acid. Our results show that polyphenol addition improved tensile strength, generally concentration- dependent and increasing with polyphenol polymerization, as a result of covalent crosslinking as shown by the SDS-PAGE. For all protein types, the 4% GSE-HP/10% glycerol formulation produced the highest tensile strength, yielding a 2.11–3.72x increase compared to their respective glycerol controls. Notably, 1% GSE-HP/10% glycerol increased strength by 2.47x over its control while maintaining elongation statistically similar to both the untreated film and layered 0.1 mm cling wrap. SEM revealed overall smoother, more cohesive surfaces in polyphenol-treated films, illustrating enhanced film integrity. Polyphenol addition also reduced water uptake across all protein films. Polyphenol effect on water vapor permeability diverged where they decreased it in soy and zein films at higher glycerol levels, but increased it in wheat, likely due to matrix heterogeneity. For example, 1% GTE/20% glycerol increased WVP by 1.48X in wheat films, whereas the same formulation reduced WVP by 16% in zein, highlighting protein- specific responses. All in all, our protein film casting conditions with phenolic additives can successfully produce robust plastic alternatives, however, high solubility due to residual formic acid limits current food-contact applications, highlighting the need for post- processing to enable safe, functional packaging solutions.