Preparation And Properties Of Chitosan-based Bacteriostatic Agents And Their Application In Strawberry And Fresh Tremella Fuciformis Bacteriostatic Preservation

Chitosan(CS)is an important renewable resource obtained from deacetylation of chitin.It has many excellent properties and can be used as a safe and feasible green bacteriostatic preservative material for the fresh storage of food.However,chitosan has high molecular weight and is insoluble in water and alkaline solution,which limits its application.In order to enhance the solubility of chitosan and expand its application,it can be chemically modified.However,the traditional chemical modification method uses a large number of organic or inorganic reagents,which is easy to pollute the environment.Therefore,in order to obtain a green,safe and environmental friendly chitosan-based antibacterial material which can be used in food antimicrobial and fresh-keeping,this paper prepared chitosan-based antimicrobial agent immobilized with natural antimicrobial substances,and explored its application effect in food antimicrobial and fresh-keeping.Chitosan was treated with 2,2,6,6-tetramethylpiperidine oxygen free radical(TEMPO)/laccase oxidation system and chitosan enzyme.TEMPO/laccase chitosan(TLCS)and chitosan-TEMPO/laccase chitosan(CTLCS)were prepared and their structures and properties were investigated.The secondary structure of TLCS and CTLCS was changed and C6 hydroxyl group was substituted by FTIR.The contents of aldehyde and carboxyl groups in TLCS and CTLCS were determined.It was found that the aldehyde and carboxyl groups in TLCS were 287.7 mmol/kg and 21.53 mmol/kg,respectively,and the degree of substitution was 5.1%.The content of aldehyde and carboxyl groups in CTLCS were 174.5 mmol/kg and 12.53 mmol/kg,respectively,and the degree of substitution was 3.1%.Compared with chitosan,the solubility of TLCS and CTLCS in aqueous solution and 1% citric acid solution was improved,the dynamic viscosity was significantly reduced,and the total antioxidant capacity of TLCS and CTLCS were increased by 3 times and 2.5 times,respectively.Cytotoxicity experiments showed that TLCS and CTLCS had no cytotoxicity.Therefore,TLCS and CTLCS can be used as solid carriers of natural antimicrobial agents to prepare water-soluble,sprayable and nontoxic chitosan-based antimicrobial agents for food preservation.Lysozyme(LSZ)and Cinnamaldehyde(CIN)were covalently combined with aldehydes and amino groups in TLCS and TLCS to prepare lysozyme-TLCS bacteriostatic agent(LSZ-TLCS),lysozyme-CTLCS bacteriostatic agent(LSZ-CTLCS),cinnamaldehyde-TLCS bacteriostatic agent(CIN-TLCS)and cinnamaldehyde-CTLCS bacteriostatic agent(CIN-CTS).The immobilization of lysozyme by TLCS and CTLCS was 49.60 mg/g and 26.41 mg/g,respectively,and the immobilization of cinnamaldehyde was 18.61 mg/g and 21.77 mg/g.FTIR,XRD and TGA showed that lysozyme and cinnamaldehyde changed the structure and crystallinity of TLCS and CTLCS by covalent bonding,and improved the thermal stability of cinnamaldehyde.Staphylococcus aureus(ATCC25923)and Escherichia coli(ATCC25922)were used to study the bacteriostatic effect of four kinds of bacteriostatic agents.It was found that all four kinds of bacteriostatic agents had bacteriostatic effect.The practical antimicrobial and fresh-keeping effects of four antimicrobial agents were studied by using strawberry and Tremella fuciformis.The results showed that the four antimicrobial agents could extened the shelf life of strawberry by 2 days,and played a positive role in the color,hardness,weight loss and pH.The four antimicrobial agents could inhibit the corruption of tremella fuciformis,but had no significant effect on the sensory,Hunter whiteness and weight loss of tremella fuciformis.In conclusion,this study provided two chitosan derivatives which could be used as carriers of natural antimicrobial agents.Four chitosan-based antimicrobial agents were prepared,which provided a basis for food antimicrobial and fresh-keeping.