A self-adhesive glutenin-based coating cross-linked by genipin for suppressing microplastic shedding in harsh environments†

The large-scale application of plastic packaging has raised concerns on the generation of microplastics (MPs). The presence of MPs in food has been increasingly reported, and plastic packaging is one of the main sources. However, few studies have focused on strategies to inhibit shedding of MPs. Herein, a simple, green, and durable coating, which was inspired from soybean milk skin, was developed to suppress MP shedding from food-grade plastics in seven harsh simulation environments (considering the five factors of heat, acid, alkali, salt, and oil). This coating was formed via the phase transition of glutenin after treatment with tris(2-carboxyethyl)phosphine, and it spontaneously adhered to any plastic surfaces under mild conditions. To improve its physical properties, genipin was used as a cross-linking coating. The performance of the cross-linked coating improved in the following aspects: (1) increase in its contact angle from 84.7° to 96.1°; (2) improvement in its tightness; (3) reduction in its roughness from 0.59 μm to 0.31 μm; (4) improvement in its elastic modulus from 19.85 GPa to 30.87 GPa; (5) improvement in its gas barrier permeance by 24.46%; and (6) and decrease in the shedding abundance of MPs by 61.14%. Notably, the inhibition rate of the cross-linked coating on MP shedding under any harsh conditions ranged from 92% to 98%. After coating, MPs with sizes exceeding 100 μm were not observed through fluorescence and micro-Raman microscopies. Moreover, the covalent crosslinking mechanism of genipin on the coating was investigated using Fourier transform infrared and X-ray photoelectron spectroscopies. Furthermore, cell proliferation was used to demonstrate the safety of the coating. Overall, this work provides new insights into the control of MPs, inspiring researchers to focus more on the front-end source and design new materials to defend against the threat of MPs to human health.