Study On The Preparation Of Methyl Jasmonate/Soy Protein Isolate Composite Membrane And Its Inhibitory Effect On Decay Incidence In Postharvest Strawberry Fruit

Soy protein isolate(SPI) is commonly used to prepare biological packaging film for its perfect film-forming ability. However, compared to the commercially available fresh-keeping films, its mechanical property and moisture barrier property is more sensitive to the external environment. In addition, since it is rich in amino acids and other nutrients, micro-organisms can grow easily which result in short shelf life and poor ability of food preservation. Therefore, the practical application of SPI film is greatly limited. However, adding some antimicrobial agents such as essential oils into SPI film can effectively improve its antimicrobial property, and inhibit microbial growth on the surface of packaged food, thereby extending the shelf life.In this thesis, the process of film formation by adding several additives into soy protein isolate as the membrane substrate was investigated. Meanwhile, the preparation of methyl jasmonate(MeJA) antimicrobial film was explored and the effect of different concentrations(MeJA) on physical properties of SPI film was investigated. Finally, its ability for preservation of strawberry fruit after harvest was evaluated. The main results are as follows:(1) Effect of glycerol, pH, temperature, reducing agent Na2SO3 and solvent ratio(ethanol:deionized water) on the appearance and mechanical properties of SPI film was investgated firstly; Accordingly, three key factors including the amount of glycerol, pH, temperature were selected for optimization of SPI film-forming condition by Box-Behnken response surface. The results showed that when the amount of glycerol added is 27% at pH 8.91 and film-forming temperature 90? the values of comprehensive performance(Strength, Modulus of elasticity, Elongation) of film can get a maximum of 20.5774.(2) By direct or mixing lipids emulsion both can prepare the aromatic protein film. The Box-Behnken response surface experiment of three factors and three levels showed the results that glycerol, pH and temperature variation had a more significant influence on the mechanical properties of SPI-lipid film. The interaction between glycerol and pH, glycerol and temperature are much greater than pH and temperature interaction for both films. SPI-lipid film had a higher mechanical strength overall, however its appearance was poor and it is difficult for post-detection. Therefore, choose the MeJA-SPI film without lipids and the optimal modification condition was proved to be when the amount of glycerol added is 32.5% at pH 7.12 and temperature 88.12 ?, under this condition, the values of comprehensive performance of film reaches a maximum of 20.5058.(3) Compared with SPI film, addition of methyl jasmonate significantly increased thickness(max 0.091 mm) and elongation, light barrier properties, mechanical strength and moisture barrier properties of the film. The structural characterization of SPI and SPI-M(0.05%) films was characterized by scanning electron microscopy, X ray diffraction, and Fourier transform infrared spectrometer analysis. Results showed that the appearance of SPI-M(0.05%) films was smooth, indicating that methyl jasmonate is compatible with soy protein isolate matrix and will not affect its internal amorphous structure. The FTIR indicated that there is a certain MeJA and SPI matrix interaction. In addition, MeJA–SPI films could effectively inhibit decay incidence in postharvest strawberry fruit and extend their shelf life.