Characterization and antibacterial of soybean protein isolate composite film with carvacrol and walnut peel extract

Abstract

In order to alleviate plastic pollution and to substitute specific conventional polymer packaging, this research deployed biodegradable soy protein isolate (SPI) as a basis to create natural polymer composite films, integrating walnut peel extract (WPE) and carvacrol (CV) for their inherent antibacterial properties. The inhibition rates of the SPI/WPE5%/CV5% composite film on E.coli and S.aureus were 99.66% and 99.52%, the DPPH radical was 73.3% and ABTS radical was 95.5%. The SPI/WPE5%/CV5% composite film also exhibited excellent UV-visible barrier properties. Compared with the pure SPI film, the tensile strength of the SPI/WPE5%/CV5% composite film increased by 89.00%, the water solubility increased by 2.67%, and the water vapor permeability was reduced by 7.69%, While the water contact angle increased by 155.93%. Fourier Transform Infrared Spectroscopy studies possibly indicate that the polyphenol-proteins in the SPI/WPE/CV composite film are bound together by hydrogen bonding. X-ray Diffraction study demonstrated that the crystallinity of the SWC films increased. Scanning Electron Microscope results revealed the surface level and internal molecular structure of the SWC films. Thermal weight analysis showed that after adding WPE and CV, the thermal properties of the SWC films improved. This study explored release of the film and found that the composite film can continuously release polyphenols, which play an antibacterial and antioxidant role.