Preparation Of Edible Film And Evaluation Of Its Antibacterial Effect

Soy protein isolate (SPI) is a kind of natural polymer, which can be used as environment-friendly, biodegradable materials. The aim of this study is to optimize the protocols for the preparation of SPI edible films, and then evaluate the bacteriostatic effects and functionalities of these films.This study prepared edible SPI and SPI-AgNO3 composite film forming dispersions (FFD) and corresponding films, which were then characterized structurally by Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and atomic force microscope (AFM) analysis. The tension strength (TS), water vapor permeability (WVP), optical properties, peroxide value (POV), bacteriostatic effects and acute toxicity of the film-forming dispersions and films were evaluated.Results showed that the addition of oleic acid (OA) promoted changes in the arrangement of groups on the surfaces of FFD particles. Microstructure analyses indicated that the OA-treated films of SPI had a rougher surface. As regards for the film properties, the addition of OA caused a decrease in TS and WVP. The mechanical and optical properties of the films were closely related with their microstructure. In addition, both pH and temperature have direct effects on the film-forming features of the FFD. The effect of SPI edible film on the antioxidative features of fat indicates that the best preservation condition of the fat is away from light. The POV of the SPI film-covered group is lower than that of the antioxidant-containing group, but is significantly higher than that of the groups without any treatment. Refreshing tests were conducted on cherry tomatoes coated with edible SPI FFD. The weight-loss rate, respiration rate and texture of cherry tomatoes were used as criteria for evaluating the refreshing effects of different FFD at ambient temperature. Results showed that the use of compound coating agents containing 5% soy protein isolate,0.3% sodium sulfite,0.2% Tween80,3% glycerol and 1% oleic acid can obtain the optimal refreshing effect. The SPI films can delay the transpiration, decrease the weight loss rate and inhibit respiratory strength significantly.The SPI-AgNO3 composite films had significant bacteriostatic effects against two representative bacteria, Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative). Acute toxicity test in mice shows that SPI-AgNO3 composite dispersions is nontoxic at low concentration.This study will help to broaden the application range of SPI and its products; it also has significance for the application of SPI in a variety of industrial fields.