Preparation Of Eugenol-carboxymethyl Chitosan/Pullulan Composite Film And Its Application In The Preservation Of Chilled Pork

China is a big country in pork production and consumption,of which fresh meat consumption accounting for more than half of the pork consumption market.With the increasing attention to pork safety and in order to reduce the risk of transmission of infectious diseases such as zoonoses caused by long-distance transportation of live livestock and poultry,chilled pork has become the main direction of pork supply and consumption.Chilled meat is fresh,hygienic,soft and elastic,but its rich nutrients make it vulnerable to microbial contamination,lipid oxidation and other factors and prone to corruption.Therefore,it is important to develop storage methods that help extend the shelf life of chilled meat.To solve the problem of easy spoilage of chilled meat during storage,we fabricated a novel composite film using carboxymethyl chitosan（CMCS）/pullulan（Pul）/eugenol（E）by casting method.The mechanical properties,barrier properties,water resistance,thermal stability and other properties of the composite films were tested to evaluate the performance,and the structure and intermolecular interaction of the composite films were explored.The composite films were applied to the preservation of chilled meat,and the physicochemical and sensory indexes,texture and volatile gas of chilled meat during storage were evaluated.The main research contents and results are as follows:（1）CMCS and Pul were mixed according to different mass ratios（5:0,4:1,3:2,2.5:2.5,2:3,1:4,0:5）to prepare CMCS/Pul composite films.Based on the evaluation of the mechanical properties,water vapor and oxygen barrier properties,and water resistance of the composite films,the preparation conditions of the composite film with better performance were selected to prepare E-CMCS/Pul composite films.The results showed that the tensile strength,flexibility,water vapor permeability and oxygen permeability of the composite film with CMCS/Pul of 2.5/2.5 were moderate,and the water resistance was good.The tensile strength was 18.00 MPa,the elongation at break was 56.44%,and the water vapor permeability（WVP）was 4.64×10^–11g/m·s·Pa,oxygen permeability（OP）was2.80×10^–4g/m²·s,so CMCS/Pul=2.5/2.5 was selected for subsequent experimental research.（2）Eugenol was added to CMCS/Pul film-forming substrate at a ratio of 1%～5%to prepare CMCS/Pul composite films containing eugenol.The rheological properties of the film-forming solution were analyzed,the structure of the composite films,the interaction between molecules,the compatibility between eugenol,CMCS and Pul were investigated,and the mechanical properties,barrier properties,water resistance,thermal stability,oxidation resistance and antibacterial properties of the composite films were evaluated.The Fourier transform infrared spectroscopy（FTIR）results showed that intermolecular hydrogen bonds were formed among E,CMCS,and Pul,which was consistent with the rheological test results.Scanning electron microscopic（SEM）images showed that eugenol was well dispersed in the CMCS/Pul matrix.X-ray diffraction spectrum（XRD）showed that eugenol had good compatibility with CMCS and Pul.Moreover,the addition of eugenol improved the thermal stability of the films,and significantly increased the antibacterial properties and antioxidant properties.When 5%eugenol was added,the WVP of the film reduced to2.41×10^–11g/m·s·Pa,and the thermal stability increased by 15℃.However,the mechanical properties of the composite films decreased after the addition of eugenol,but the mechanical properties of the composite film containing 4%eugenol were better,the tensile strength was19.56 MPa,and the elongation at break was 36.62%,which was confirmed by the SEM.（3）CMCS/Pul composite films with different eugenol content（0%～5%）were used in chilled meat preservation experiment.The changes of physical and chemical indexes such as aerobic plate count,TVB-N value,TBARS value and p H value of chilled meat during storage were measured,and the sensory properties,texture properties and volatile gas changes were evaluated.The results showed that the CMCS/Pul composite film containing5%eugenol could significantly delay the increase of the aerobic plate count,TVB-N value,TBARS value and p H value of chilled meat compared with the control group,and slow down the the deterioration of texture characteristics and the generation of putrid odor of chilled meat,thus prolonging the freshness of chilled meat.