| Salmon meat has high water content,rich in protein and polyunsaturated fatty acids,and has high nutritional value.It is popular with consumers,but it is easy to breed microorganisms and be oxidized,and its shelf life in cold storage condition is very short.As a kind of raw food diet,it is delicious and has dense taste,but frozen storage will make it lose its dense texture and taste.Therefore,it is very necessary to extend the shelf life of salmon in cold storage with temperature higher than 0℃.Coating foods with edible film is a good food preservating method.Considering the high moisture content of salmon,curdlan(CL)with certain hydrophobicity was used as the base material to prepare certain water-resistant and flexible edible films through the screening of plasticizers.Condidered the short shelf life of salmon meat caused by its high tendency of microbial breeding and oxidative rancidity,antioxidants and antibacterial agents were added in order to prepare water-resistant and flexible CL-based edible films with anti-oxidation and antibacterial activity,and their effects on the structure and properties of the edible film were further studied,this research could enrich the functional and active packaging system and prolong the refrigerated shelf life of salmon fillets.The main research content and results are as follows:(1)The effects of different plasticizers—glycerol(GLY),ethylene glycol(EG),propylene glycol(PRO),xylitol(XY),sorbitol(SOR)and polyethylene glycol(PEG)on the structure and physical properties of CL edible films were studied.The results showed that the crystallization peak of the film changed when PEG and XY were added,and the addition of all plasticizers reduced the crystallinity of the film,and the crystallinity of the film with PRO decreased most obviously.The addition of all plasticizers improved the roughness of the surface and section of the film,and the surface and section of the CL-GLY film were the smoothest.Plasticizers reduced the number of hydrogen bonds in the CL film.Plasticizers reduced the number of glass transition temperatures of CL molecules in the film,and lowered the main glass transition temperature.The addition of plasticizer increased the light transmittance,oxygen permeability,WVP value and water solubility of CL film,but the film still had good water resistance and barrier property.The plasticizer reduced the swelling rate of the CL film.The tensile strength and elongation at break of the film increased after adding plasticizers GLY,PEG and EG,indicating that these plasticizers improved the flexibility of the film,and the improvement of GLY was the most obvious.In summary,the CL-GLY film with optimal mechanical properties and certain water resistance property can be obtained by adding GLY.(2)The effects of different antioxidants—ascorbic acid(AA),tea polyphenols(TP),curcumin(CUR),ferulic acid(FA)and protocatechuic acid(PA)on strctuctures,physical properties and antioxidant properties of CL/glycerol(CLG)edible films were further investigated.Adding PA and FA changed the crystallization form of the film,all the antioxidants reduced the crystallinity of the film,and the crystallinity of the film with FA decreased most obviously.The films containing AA,PA and CUR had increased surface roughness.The roughness of the cross-section of the films with PA,CUR,and FA increased,and the structure was not dense.PA increased the number of hydrogen bonds in the CLG film.All antioxidants except FA increased the main glass transition temperature of the film.After adding TP and CUR,the light transmittance of the film of decreased,while after adding FA,PA,AA,the light transmittance of the film increased.The addition of antioxidants decreased the WVP value of CLG film and increased the contact angle,water solubility and oxygen permeability of CLG film.The contact angle of CLG-FA film was the largest.FA,PA,AA reduced the swelling rate of CLG film.The water content of CLG film with FA and PA remained unchanged.The addition of antioxidants increased the tensile strength of CLG film and decreased the elongation at break.Among them,the elongation at break of the film with FA,PA,and CUR decreased not that much.The DPPH and ABTS scavenging rate of the films increased after the addition of antioxidants,indicating that the antioxidant performance of the films was enhanced,and the films with FA had the highest free radical scavenging rate.In summary,the CLG-FA film which had the best anti-oxidant property,good mechanical properties and certain water resistance property was obtained.(3)The effects of antimicrobial agents—glycine(GL),lysine(LYS),thyme essential oil(TEO),cinnamon essential oil(CEO),nisin(NISIN)and natamycin(NA)on the structures,physical properties,antioxidant and antibacterial properties of CL/glycerol/Effects of ferulic acid(CLGF)film were studied.The results showed that the crystallization form of the film was changed when NA was added,and the crystallinity of the film was increased by the addition of all antibacterial agents.All antibacterial agents increased the surface roughness of the film,and the addition of NA increased the cross-section roughness of the film.All antibacterial agents except NA reduced the number of hydrogen bonds in the CLGF film.Antimicrobials increased the primary glass transition temperature of CLGF film.The addition of antibacterial agent reduced the light transmittance and swelling rate of the film.Increased oxygen permeability of CLGF film.TEO,CEO,NISIN films decreased the WVP values of CLGF.GL,TEO,CEO,and NISIN reduced the water solubility of the film.TEO increased the contact angle of the film,and other antibacterial agents reduced the contact angle of the film.GL,TEO,CEO,NISIN increased the tensile strength of the film,and all antibacterial agents decreased the elongation at break of the film.Adding TEO or CEO,the anti-oxidant property of the film was slightly enhanced,and the anti-oxidant property of the film with NISIN was not significantly changed.Antibacterial agents increased the antibacterial properties of the films against Escherichia coli and Staphylococcus aureus,and the film with NISIN showed the strongest antibacterial properties against both bacteria.To sum up,after adding Nisin,the CLGF film with the best antibacterial performance could be obtained,and this film still had excellent anti-oxidant property,good mechanical properties and certain water resistance property.(4)The effect of CLG,CLGF,CLGF-GL,CLGF-LYS,CLGF-TEO,CLGF-CEO,CLGF-NISIN and CLGF-NA edible film-coating on the refrigeration quality of salmon fillets were studied.The results showed that the edible films containing antibacterial agents could delay the deterioration of salmon meat.To be specific,the change of pH value of salmon meat was delayed and the increasing extent of TBA value were decreased,the increase of hardness,cohesiveness and chewiness of salmon meat were delayed,the decrease of elasticity was slowed,and the weight loss rate and number of clump count of salmon meat were decreased.On the whole,CLGF-NISIN edible packaging had the best preservation effect on salmon fillets. |
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