| More and more attentions have been focused on the edible films due to the enhancement of people’s environmental and food safety awareness. Soy protein isolated (SPI) has attracted progressively increasing interest of the researchers for it’s excellent film-forming property, biodegradability, edibility, nutritional and good barrier characteristics against gas, oil, et al.In this thesis, the SPI films was prepared with SPI as a substrate and TGase as a modifier. To optimize the films preparation conditions, the mechanical properties, water vapor and oxygen permeability were selected as the film quality indexes. The effects of the concentration of SPI and enzyme, the kinds and addition of plasticizer, pH and drying temperature on the above film quality indexes were evaluated and then the preferred options were confirmed. Furthermore, using the mechanical properties as the index, the optimization for the technology parameters of TGase modification and SPI films-forming conditions were implemented. The changes of film’s structure, composition due to modification were studied with SDS-PAGE electrophoresis apparatus, UV-VIS, X-ray diffraction, FTIR and SEM. In the last step, the application properties of the protein film on the edible packing material was explored. The main results were as follows:(1) Based on the results of the single factor experiments, using the mechanical properties of the films as the index, the SPI film-forming conditions were optimized through the response experiments design with the factors such as pH and the addition of SPI, TGase and glycerol.The optimal modification SPI film-forming condition was proved to be:pH8.07, the addition of SPI, TGase and glycerol was5.01%,0.27%and2.30%, respectively. Under this condition, The values of TS and EB of the modified SPI films were3.25±0.05MPa and146±0.56%, respectively. The Chi-square test was used to verify the deviation between the actual and theoretical values,the result showed that the deviation was not significant(P>0.05), the binomial regression model can better reflect the formation process of the TGase-modified SPI film.(2) The material composition and structure of the CK film and TGase-modified SPI film were charactered through the tests of SDS-PAGE electrophoresis apparatus, UV-Vis, X-ray diffraction, FTIR and SEM. The results showed as follows:compared with CK, the proteins molecule of the SPI film appeared cross-linking; the amount of effective lysine reduced, whereas the degree of crystallinity increased after modification by transglutaminase. The FTIR-spectrums test showed that after TGase-modification, the secondary structure of SPI changed, i.e. the ratio of a-helix or random coils increased. The changes of the secondary structure explained the improvement of the tensile strength of TGase-modified SPI films. The SEM test showed that the uniform and compactness of the films were enhanced after TGase modification.(3) The preliminary application possibility of SPI films in food packaging was studied. Compared with the PVC plastic packaging film, the mechanical strength and the barrier characteristics against oil of TGase-modified SPI films were inferior, whereas the barrier characteristics against gas were better. Moreover, according to the tests of the water sorption isotherm, the TGase-modified SPI films could be applied under the condition of the relative humidity ranges33%-62%. Thus, more detail considerations such as the hydrophilic group of SPI films and the food quality requirements are necessary during the application of the TGase-modified SPI films in the food packaging. |
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