Properties of Soy Protein Isolated Films and Release of Antimicrobial from Films into Fatty Food Simulants
|Keywords||Soy protein isolate films barrier property antimicrobial active packaging release limited packaging-limited food model diffusion coeffecient partition coefficient|
Foodborne disease is one of the most common diseases in the world. This disease is usually caused by the food contaminated by the microorganism or chemical substances. Most diseases of human being and livestocks are ascribed to the bacteria, which account for 85～90%of the diseases induced by microorganism. The bacteria do serious harm to human being’s health, which is one of the key factors that affect the shelf life of food. In recent years, the study of the bacteria control, as well as the exploitation of the new antimicrobial and antimicrobial packaging material has become a fascinating field of research. The selection of natural antimicrobials (AMs), determination of their characteristics, detection of releasing amounts and kinetic analysis have been studied in this thesis, which includes:The Microplate Reader with a sterile 96-well microtitre plate was used to detect the antimicrobial activities of nine kinds of substances. By this method, six kinds of more effective agents were sieved. The activities ranking of selected antimicrobial agents against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Listeria monocytohenes (L. mono), Salmonella enteritidis (S. enteritidis), Yersinia enterocolitica (Y. enterocolitica) and Shigella sonnei (Sh. sonnei) were cinnamaldehyde (Cin)> isoeugenol (Iso)> thymol (Thy)> eugenol (Eug)> vanillin (Van)> guaiacol (Gua).Antimicrobial-soy protein isolate (AM-SPI) films were prepared. AM-SPI films showed ideal bacteriostat effect after examination of the films’bacteriostat rates, bacteriostat zone and the packaging experiments of meat products. Cin, Iso, Thy, Eug and Van were identified as the finaly antimicrobials. Their concentration for vanillin, cinnamaldehyde, eugenol, isoeugenol and thymol in SPI films was 0.35,0.30,0.35,0.25 and 0.25%, respectively. Their mechanical properties such as elongation at break (ELO), tensile strength (TS) were determined. The water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of SPI films under different RH and temperatures were studied. The WVTR and OTR values were compared with those of other packaging material—polyethylene (PE) film, polyproplene (PP) film and polyvinyl alcohol (PVOH) film. The result show that the SPI films are Non-Fickian materials and their WVTR/OTR satisfied exponential relationship (y=Aexp (x/B)+C, where x was environment relative humidity). The addition of Van, Cin, Eug, Iso and Thy has negative effects on mechanical performance and permeability properties of SPI films. The stabilities of Van, Cin, Eug, Iso and Thy in olive oil were determined. Results indicated that the antimicrobials showed good stabilities in 5,20,40,60℃respectively. After 10 days, loss rates of AM were smaller than 12%. There was no new peak found in the chromatogram of phenolic compounds analyzed after 30 days of storage. Thus, phenolic compounds losses might be due to the frequent opening of the cap during the process of sampling instead of the chemical instability of phenolic compounds. The losses could be minimized if sampling is done promptly and efficiently. The release of AM from the SPI films contained certain amount of natural antimicrobials into olive oil in different temperatures was studied. For the above experiments, olive oil was sampled systematically and than treated. Afterwards they were analyzed by high performance liquid chromatography with UV-vis detection. The detection wavelength was set at 230 nm and 280 nm. The flow rate of 1.0 mL/min was used. The column temperature was held at 40℃. Samples were eluted according to the method (0 min,25%acetonitrile and 75%water; 30 min,50%acetonitrile and 50%water; 35 min,25% acetonitrile and 75%water; 40 min,25%acetonitrile and 75%water). The detection of limit, accuracy and recovery of the testing method have been investigated.The partition coefficient (KF,P) of AM between the SPI films and olive oil was calculated by dividing the concentration in the food simulants by the concentration left in the film when the equilibrium was reached. The diffusion coefficient (DP) of AM in the SPI films was determined by fitting the release model of the limited packaging-limited food system to the experimental data. The limited packaging-limited food system model was proved to be able to predict the AM release under given conditions. Based on this, the impacts of the temperature, the structure and polarity on KF,P and DP have been analyzed. The results showed that the higher the temperature was, the higher the release rate of antimicrobial would be. The high regression coefficients suggested that the Arrhennius equation could adequately describe the relationships between the temperature and thymol’s release rate. KF,P of AM was inversely proportional to the temperature. The activation energy of diffusion for Van, Cin, Eug, Iso and Thy was found to be 18.3249,57.3392,52.4339,53.9238 and 55.9217 kJ/mol, respectively. In the selected antimicrobial, the effect of temperature on the diffusion coeffecient of Van is smaller than other antimicrobial. The release quantity of AM from SPI films into olive oil at 30℃was compared with the predicted values by the imited packaging-limited food model.