Study On The Film Properties Of Chitosan-grafted-phenolic Acids And Its Preservation Effect On Agaricus Bisporus

Chitosan(CS)can be used as a novel edible film instead of traditional packaging material due to its good film-forming property.However,the lack of its biological activity greatly limits application because of the special biological macromolecular structure of chitosan and the defects of its hydrogen atom donor.In this study,gallic acid(GLA),caffeic acid(CA),gentisate acid(GTA)and sinapic acid(SA)were grafted onto chitosan by 1-(3-dimethylaminopropyl)-3-ethylcarbinimide hydrochloride(EDC)/1-hydroxybenzotriazole(HOBt)chemical crosslinking method.The conjugates were prepared into films further.By comparing the physical and chemical properties,antioxidant and antibacterial activities of chitosan-grafted-phenolic acid films,caffeic acid-grafted-chitosan(CA-g-CS)film with better comprehensive properties were screened and its preservation effect on Agaricus bisporus was evaluated.The main findings are as follows:(1)Four phenolic acid-grafted-chitosan conjugates were prepared with different phenolic acids via EDC/HOBt,and their characteristics were analyzed.Furthermore,the antioxidant and antimicrobial activities of conjugates were compared to screen out the optimal conjugates.The substitution degree and antioxidant activity of CA-g-CS and gallic acid-grafted-chitosan(GLA-g-CS)had significantly(P<0.05)higher than CS and other two conjugates.The characterization analysis showed that the UV absorption peaks of CA-g-CS were stronger than that of GLA-g-CS.In addition to all proton signals of chitosan,these conjugates showed new absorption peaks between 6.2-7.5ppm,corresponding to aromatic protons of phenolic acids.The antioxidant and antimicrobial activities of these conjugates were significantly enhanced,and both GLA-g-CS and CA-g-CS showed stronger antioxidant activity.In addition,bacteriostatic ability of CA-g-CS was significantly stronger than that of GLA-g-CS.(2)GLA-g-CS and CA-g-CS were further developed into films by casting and were characterized in terms of appearance,structure,and mechanical and barrier properties,as well as antioxidant and antimicrobial activities.The results showed that the CA-g-CS film exhibited the highest tensile strength(10.67±0.47 MPa)and elongation at break and had desirable barrier properties against water vapour and oxygen(0.70±0.02 g mm/m~2h k Pa and 37.72±0.23 meq/kg,respectively).In addition,both the GA-g-CS and CA-g-CS films displayed higher antioxidant activity than the CS films,while CA-g-CS also exhibited a significantly stronger(P<0.05)inhibitory effect on Bacillus subtilis(G~+)and Staphylococcus aureus(G~+).These findings will contribute to a theoretical basis for the development of the CA-g-CS film into food packaging.(3)CA-g-CS coated on HDPE film was used as a novel active packaging material for Agaricus bisporus preservation.The effect of HDPE/CA-g-CS film on physicochemical indexes of Agaricus bisporus during cold storage were measured.As the result showed,HDPE/CA-g-CS film displayed higher hardness and whiteness,and the lower respiration rate compared with commercial HDPE film,which means that HDPE/CA-g-CS film can maintain the quality of Agaricus bisporus during storage.