| The sea bass（Lateolabrax japonicus）has high nutritional value and is popular with consumers.However,sea bass is easy to deteriorate,which is mainly caused by the oxidation of lipid and protein,the growth of microorganism and the degradation of enzyme,which limits the transportation and shelf life of fresh sea bass.Therefore,it is particularly important to find an effective method to keep the quality of sea bass during refrigeration and extend the shelf life.The main research contents of this paper are as follows:first,the antibacterial effect of Melissa officinalis L.essential oil on Vibrio parahaemolyticus and Shewanella putrefaciens was studied by the changes of cell membranes and biofilms.Second,physicochemical propertiesg of the active film,which was made of Melissa officinalis L.essential oil combined with locust bean gum and carboxymethyl chitosan,was analyzed.Third,the active coating made of Melissa officinalis L.essential oil combined with locust bean gum and carboxymethyl chitosan was applied to the sea bass under cold storage,and the effects of the active coating on sea bass with the quality,physical and chemical properties,lipid oxidation and protein structure of sea bass during cold storage were studied.Finally,based on the Cl O2combined with active coating,the changes of quality and physicochemical properties of sea bass during cold storage were studied.The main research contents and conclusions are as follows:1.To study the antibacterial activity and mechanism of Melissa officinalis L.essential oil.Taking Vibrio parahaemolyticus and Shewanella putrefaciens as research objects,the minimum inhibitory concentrations（MIC）of the two kinds of bacteria were obtained through the broth microdilution method.0.25×MIC,0.5×MIC,1×MIC,2×MIC Melissa officinalis L.essential oil were respectively added to Vibrio parahaemolyticus and Shewanella putrefaciens to study the bacteriostatic mechanism of Melissa officinalis L.essential oil.The results showed that,the content of nucleic acid and protein significantly increased,the electrical conductivity increased and the cell activity decreased after Melissa officinalis L.essential oil treated.Through the analysis of transmission electron microscope and scanning electron microscope images,it could be seen that the complete and smooth cells appeared dents and folds.The cell wall was destroyed by Melissa officinalis L.essential oil,the permeability of the cell membrane was increased,flowing out the cell content and causing cell death.The amount of biofilm on Vibrio parahaemolyticus and Shewanella putrefaciens were decreased,and the content of extracellular polysaccharide was also decreased.The growth environment and nutrients of biofilm were damaged with the addition of Melissa officinalis L.essential oil,and the adhesion of biofilm was reduced.2.To study the preparation and properties of the active film of Melissa officinalis L.essential oil combined with locust bean gum and carboxymethyl chitosan.Taking1×MIC,2×MIC,4×MIC Melissa officinalis L.essential oil into nanoemulsions,and combined with locust bean gum and carboxymethyl chitosan which were used as film-forming substrate.The results showed that:the Melissa officinalis L.essential oil nanoemulsions improved the breaking elongation,water resistance and hydrophilicity of the active films.The elongation at break of the active films containing 0.4%Melissa officinalis L.essential oil nanoemulsions was increased from 18.49%to27.97%and the water resistance was decreased from 56.32%to 25.43%,and the water contact angle was increased from 75.13 to 83.86.Scanning electron microscope image and Fourier transform infrared spectrum analysis showed that the Melissa officinalis L.essential oil nanoemulsions was very compatible with the film-forming substrate,and the essential oil was evenly dispersed in the film.At the same time,the anti-oxidation and antibacterial activities of the active films were significantly enhanced with the added concentration of Melissa officinalis L.essential oil.3.To evaluate the fresh-keeping effects of Melissa officinalis L.essential oil nanoemulsions-locust bean gum-carboxymethyl chitosan active coating on sea bass during cold storage.0.5×MIC,1×MIC and 2×MIC Melissa officinalis L.essential oil into nanoemulsions,and combined with locust bean gum and carboxymethyl chitosan which were used as film-forming substrate.The active coating was prepared.The sea bass was soaked and kept at 4℃refrigeration.The changes of sea bass on microorganisms,physical and chemical properties,volatile flavor compounds during the cold storage of were studied.The results showed that:compared with the control,the growth of microorganisms and odor compounds of sea bass was inhibited by the treatment of active coating.At the same time,the degradation of freshness amino acids such as glutamic acid and alanine was slowed down,and the growth of histidine was inhibited.The shelf life of sea bass in the control group was 6 d,and that in the treatment group with locust bean gum-carboxymethyl chitosan active coating and 0.5×MIC,1×MIC,2×MIC Melissa officinalis L.essential oil nanoemulsions-locust bean gum-carboxymethyl chitosan active coating were 6 d,9 d,12 d and 15 d,respectively.According to the sensory analysis results,the sea bass treated with active coating containing 1×MIC Melissa officinalis L.essential oil nanoemulsions was the best treatment.4.To evaluate the effects on lipid oxidation and protein structure of Melissa officinalis L.essential oil nanoemulsions-locust bean gum-carboxymethyl chitosan active coating treated sea bass during cold storage.After the same treatment as above,.the changes of sea bass on lipid conservation and protein structure during cold storage were studied.The results showed that:the treatment of Melissa officinalis L.essential oil nanoemulsions-locust bean gum-carboxymethyl chitosan active coating controlled the oxidation of lipid,significantly reduced the centrifugal loss of fish,and effectively delayed the changes of water activity and water migration.The results of carbonyl,sulfhydryl and laser confocal analysis showed that the coating treatment could reduce the oxidative degradation of sea bass protein during cold storage.5.To evaluate the fresh-keeping effects of Cl O2pretreatment combined with the active coating of Melissa officinalis L.essential oil nanoemulsions-locust bean gum-carboxymethyl chitosan on sea bass during cold storage.Soaking sea bass fillets with 0.5 mg/L Cl O2for 10 minutes,then immersion of sea bass with active coating containing 1×MIC Melissa officinalis L.essential oil nanoemulsions,and stored at 4℃.The changes of microorganism and physical and chemical properties of sea bass during cold storage were studied.The results showed that,Cl O2decelerated the growth of microorganisms during storage,the combination of active coating containing Melissa officinalis L.essential oil and Cl O2had better fresh-keeping effects than that of single treatment,the growth of odor compounds was significantly inhibited.The shelf life of sea bass in the control group was 9 d,and the shelf life of sea bass treated by Cl O2,Melissa officinalis L.essential oil active coating treatment group and Cl O2-Melissa officinalis L.essential oil active coating were 12 d,15 d and18 d respectively. |
