Heterogeneity in Diameters of Protein Fibrils and Chitosan for a High CO₂/O₂ Selectivity and Desired Mechanical Properties of Edible Bioplastic Films

Edible bioplastics offer a possible approach with great potential to address the challenges of plastic and microplastic crisis and the issue of food waste. In the present study, in situ, induction of fibrillation of legume proteins within chitosan matrix is found to form edible bioplastic films with a high CO₂/O₂ selectivity coefficient of ≈130. Desirable mechanical properties, including a high elongation at break of ≈230%, are realized to fabricate shopping bags, which can be filled with 5 kg of fruits. An atmosphere with a high CO₂ content and low O₂ concentration is spontaneously achieved after strawberries are packaged with the films and ≈85% of the fruits are edible after 9 days. The contents of CO₂ in the equilibrium state and the percent of edible fruits are positively correlated with the CO₂/O₂ selectivity of the films. By comparison of the edible bioplastic films made from mung bean protein (MP) and pea protein (PP), the fibrillation capability of legume proteins and the heterogeneity in polydisperse diameters of the protein fibrils and chitosan are demonstrated to make great contributions to the dense microstructure, leading to the strong mechanical properties and high gas selectivity of the films. The structure-property relationship is elucidated for high-performance bioplastics films.