Wet-heating Maillard reaction as an approach to enhance the mechanical and water-resistance properties of protein-based edible films

Protein-based edible films provide considerable potential as alternatives to plastic packaging, but their inferior mechanical and water-resistance properties have hindered their application in the food industry. Maillard reaction (MR), which irreversibly alters the structure of proteins by covalently binding amino groups on protein chains with carbonyl groups on reducing sugars in the presence of heat, holds great promise for enhancing the film-forming properties of proteins. In this study, wet-heating was applied to pea protein isolate (PPI) and pullulan (90 ℃ for 2 - 48 h), and the properties of PPI-based films were evaluated. Especially, PPI treated by heat alone for 2 - 48 h was investigated as a positive control, which allowed us to demonstrate the simultaneous effect of heating and MR. The results showed that MR generated Maillard reaction products with a brown color. Additionally, we observed that both heating and MR played roles in improving film properties. The heating effect significantly increased the tensile strength from 1.42 MPa (unheated PPI film) to 2.58 MPa (4 h of heating) and decreased water vapor permeability from 1.72 to 0.72 g mm h-1 m-2 kPa-1. Meanwhile, the MR with pullulan significantly enhanced elongation at break and water contact angle of films (increasing to a maximum of 353.21% and 104.35°, respectively), comparable to or surpassing films based on synthetic polymers. These findings illustrated the distinct roles of heating and MR in enhancing the packaging properties of protein-based films and provided new insights into the application of MR in the food industry.