Development and characterization of soy protein isolate-based emulsion films with green sichuan pepper essential oil: Functional and structural insights

Soy protein isolate (SPI)-based films had limited application due to high water vapor permeability (WVP), weak antioxidant and antibacterial activity. Herein, the green sichuan pepper essential oil (GSPO) with natural antibacterial and antioxidant effects was added in SPI to prepare SPI-GSPO emulsion film, and the physicochemical properties and antioxidant/antibacterial activity of SPI-GSPO emulsion films were comprehensively evaluated. The results showed that the particle size of SPI-GSPO pre-emulsions decreased and the zeta potential increased as the increasing content of GSPO, providing a well-structured pre-emulsion for the preparation of film. The transparency value, L* and a* of films improved, while the b*, swelling ratio (SR), water solubility (WS), WVP, moisture content (MC), and Delta E decreased due to more hydrogen bonds formation that replaced hydrophilicity interaction when GSPO incorporated into SPI film. The antibacterial activity of SPI-GSPO emulsion film enhanced with the incorporation of GSPO. Furthermore, the mechanical properties, including tensile strength (TS), elongation at break (EAB), and antioxidant activity improved with GSPO added and reached the maximum value of SPI-GSPO-1.0 emulsion film. Meanwhile, the upper surface and cross-section structure of SPI-GSPO-1.0 emulsion film showed smooth and uniform. Overall, it was an effective method to promote the antioxidant, antibacterial activity, and mechanical strength of emulsion films by adding GSPO.