| The film-forming technology and condition of soy protein/ polyvinyl alcohol were systematically studied. The effect of adding method solvent、soy protein content、polyvinyl alcohol content、glycerol content and pH on the properties of the film were studied through single-factor experiments,using ordinary soy protein and polyvinyl alcohol as mainly materials. Response surface methodology was carried out to optimize the technology and condition of soy protein/ polyvinyl alcohol film.,and the mathematical model was established. The artical also investigated the effect of reducing agents、intensifiers and surface-active agents on the properties of the film. The properties of the film were improved using L9(34)orthogonal experiment design ; the structure of the soy proteirn/ polyvinyl alcohol film and the film modified was characterized through differential scanning calorimetry(DSC)、infrared spectroscopy ( FT-IR )、scanning electron microscope(SEM); the degradation properties of the film improved and unimproved were studied through buring experiments; also, the film’s preservation effect were evaluated,using hami melon as packaging content. The main aspects and results were represented as follows:1.The single-factor experiments results showed: After melting the soy protein and polyvinyl alcohol with distilled water, leach the polyvinyl alcohol into the soy protein, then add 30 mL ethanol into the mixed solution, which would make the solution vacuumized easily, and make the film much more stronger; the film was obtained easily when soy protein content was 2.0%-5.0%. When the soy protein content was 3.0%, the integrated grade was highest. When the polyvinyl alcohol content was 3.0%, the integrated grade was highest.If 2.0% glycerol was added, the properties of the film were optimal. Under alkaline condition, the films were yellow, the colour aggravated dark while the pH increased.When pH was 8.0, the integrated grade was higher and the colour was lighter. At pH 8.0 the film had better properties.2.The response surface methodology was designed, using soy protein content、polyvinyl alcohol content and pH as factors. The result showed: The optimal content of soy protein、polyvinyl alcohol and pH were 2.87%, 3.19%, and 8.65 respectively. The tensile strength、elongation、transmittance and water absorption of the films under the optimal technology were 5.41Mpa, 40.60%, 29.57% and 66.70% respectively and its integrated grade was 0.689. The regression equation of integrated grade with soy protein content、polyvinyl alcohol content and pH wasy=0.45-0.083X1+0.15X2+0.067X3+0.022X1X2+0.013X1X3-0.03X2X3+0.022X12-0.016X22+0.023X32.The R2 of the regression equation was 0.9973.3.The effect of agents on the properties of the films was investigated. The results showed that the best reducing agent was sodium sulfite anhydrous,and its suiltable content was 0.15%; the best surface-active agent was sodium dodecylbenzenesulfonate, and its content was 0.125%; the best intensifier was gelatin, and its optimal content was 0.200%. The L(934)orthogonal experiment showed that the optimal combination of the factors was: sodium sulfite anhydrous was 0.15%, sodium dodecylbenzenesulfonate was 0.125%, gelatin was 0.25%.4.The structures of the soy protein/ polyvinyl alcohol film modified and unmodified were characterizated, using DSC、FT-IR and SEM. The result showed that soy protein and polyvinyl alcohol can fused at a certain extent, but they couldn’t distributed uniformly, there was micro phase separation between soy protein and polyvinyl alcohol. The film modified by agents had a better homogeneous structure, and the soy protein and polyvinyl alcohol molecular combined into a three-dimensional net structure.5.The degradation properties of the soy protein/ polyvinyl alcohol film improved and unimproved were studied through buring experiments.Under constant temperature and humidity, the weight loss of soy protein/ polyvinyl alcohol film indoor was 65.9%,and the modified film was 66.9% after 131 days. Under natural conditions,the weight loss of soy protein/ polyvinyl alcohol film outdoor was 69.4%,and the modified film was 70.7% after 131 days.6. The preservation effect of film on melon indicated: with the storage time prolonged, the weight loss of Hami melon continued to increase, the weight loss of the melon wrapped by modified film was lower than wrapped by soybean protein / polyvinyl alcohol film; in the first five days, the rigidity of each grop was lower than the controlled group, in the sixth and seventh days, the rigidity of controlled group dropped considerably; compared with the controlled group, the Vc content of the melon wrapped with degradable film decreased relatively fewer; the pH of each grop presented a trent :first falling and then rising, the controlled group decreased most; soluble solids content of the controlled group, the group wrapped with degradable films increased firstly and then dropped, from sixth to seventh day ,it prsented a slight upward trend. |
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