| The environmentally friendly active packaging materials loaded with bioactive substances,composed of natural biopolymers,have become a research hotspot in the field of food packaging in recent years.In this study,Pickering emulsion was introduced as the loading system of cinnamon essential oil,and the covalent complex of zein and gallic acid（GA）prepared by alkali treatment was used as an emulsifier to stabilize cinnamon essential oil Pickering emulsion（ZGPE）.Then,the effects of different loading amounts of ZGPE on the properties of matrix chitosan（CS）after film-forming were studied.Finally,the ZGPE/CS proportion with the best comprehensive performance was selected to prepare the emulsion based active coating solution,which was used in the postharvest storage of mango to evaluate its practical application value.The main results were as follows:（1）The zein-GA covalent complex was prepared in the aqueous phase with a p H of 12.0 by alkali treatment.The results showed that the binding amount of zein to GA was 33.25 mg/g;the content of free amino groups in zein-GA complex decreased by45%compared with zein due to the covalently binding with GA,and the electrophoresis results indicated that the relative molecular weight of the complex increased.The covalent reaction also reduced theα-helix structure in the secondary structure of zein by 10.5%,and increased the content of unordered curl by 2.9%.The Fourier transform infrared spectroscopy（FTIR）of zein-GA showed a red shift in the amide band and a quenching phenomenon in the fluorescence spectrum,indicating that the mechanism of the preparation of protein-polyphenol covalent by alkali treatment is the reaction of quinone formed by polyphenol oxidation with protein nucleophile group.In addition,the particle size distribution of ZGPE prepared by the covalent zein-GA complex as emulsifier was uniform,the particle size was 2.58μm,and the Zeta potential was 43.25m V.（2）The emulsion based active film was prepared by solvent casting method using ZGPE and CS as the film-forming matrix,then its structural characteristics and physicochemical properties were characterized in order to explore the effect of different ZGPE loading amounts on the properties of matrix CS after film-formation.The results showed that the loading of ZGPE could fill the gaps in the CS matrix,making its network structure more compact,which is conducive to the formation of a uniform and stable composite film.When the addition of ZGPE was 7.5 m L（15%,v/v）,the active film had the best mechanical properties,the tensile strength was 21.14 MPa,and the elongation at break was 37.13%;the best gas barrier performance,water vapor and oxygen transmission rate were 7.00×10-7 g/m·s·Pa and 6.07×10-8 g/m·s·Pa,respectively.In addition,the FTIR,X-ray diffraction（XRD）and scanning electron microscopy（SEM）showed that the interaction between the film-forming matrix polymers was strong,and the thermogravimetric analysis（TG）showed that the thermal stability of the active film was increased.Furthermore,the loading of ZGPE improved the shortcoming of swelling of the CS matrix after film-formation,and increased the hydrophobicity of the surface of the active film;and the cinnamon essential oil loaded in the active film showed slow-release characteristics in the food simulant solution,which could provide long-term antibacterial and antioxidant activity.（3）ZGPE and CS were homogeneously blended to form emulsion based active coating solution and applied to the surface of mangos by impregnation.The performance of emulsion based active film in practical fresh-keeping application was studied by measuring the changes of physiological indexes during storage time.The results showed that during the 10-day storage cycle,the weight loss rate,respiratory intensity,p H value,hardness and soluble solids of mangos in the emulsion based active coating group were better than those in the control group.In addition,the emulsion based active coating could also stimulate the activities of superoxide dismutase（SOD）and catalase（CAT）in mango fruit,reduce the accumulation of malondialdehyde（MDA）in the body,inhibit the attack of reactive oxygen species on tissue cells,and better maintain the integrity of fruit tissue cells.At the same time,the existence of cinnamon essential oil also prevented the invasion of microorganisms during storage.To sum up,the active film loaded with ZGPE can effectively maintain the postharvest storage quality of mango and prolong its shelf life. |
PDF Full Text Request