The Effect Of Modified Atmosphere Packaging And Coating Process On The Quality Of Frozen Tilapia Fillets

In China,the production of tilapia is rich.But the processing methods are very single,which mainly is composed of frozen the whole fish and frozen tilapia fillets.During the storage,side effects such as pollution of harmful bacteria and endogenous enzyme activities can often lead to fat oxidation and protein denaturation of tilapia products,which seriously affect the edible quality.Modified atmosphere packaging can prevent microbes breeding and reduce lipid enzymatic reaction by changing the gas atmosphere of food during storage,so as to prolong the shelf life on purpose.Edible film is a kind of high mechanical properties and permeability selection film.It can keep the quality of the products mainly by preventing migration of gas and flavor substances in storage.Based on the specific biological material as the matrix,at the same time edible film carry special additives such as plasticizer,bacteriostatic agent,antioxidant,antifreeze,preservative to slow down protein denaturation,drying loss,fat oxidation and other adverse reactions of aquatic products during frozen storage.What's more,edible film can better maintain the aquatic product quality to meet people's demand for nutrients.In the study,tilapia is taken as test object through gas packaging and edible coating to improve the quality of frozen tilapia fillets,specific conclusions are as follows:1 In order to study the effect of ice glazing on quality of frozen tilapia fillets,an experiment is designed by the indexs of hardness,Ca²⁺-ATPase activity,whiteness value,water holding capacity and TBA value,TVB-N value.Results show that the hardness,Ca²⁺-ATPase activity,whiteness value and water holding capacity of frozen tilapia fillets decline obviously in the first 30 days.Meanwhine,the hardness,Ca²⁺-ATPase activity and whiteness value of frozen tilapia fillets treated by ice glaze are significantly higher than the control group,but the water holding capacity is not obvious.Accompany with the extension of frozen time,TVB-N vaiue and TBA value of the frozen tilapia fillets are increasing,and the level of ice glazing group are significantly lower than that of control group?p<0.01?.After frozen 90 days,the TVB-N vaiue of ice glazing group is 18.11 mg/100 g,which is considerably below the 19.32 mg/100 g of control group.What's more,TVB-N value of the two groups of samples does not exceed safe limits of 20.00 mg/100 g.After frozen 60 d and 75 d respectively,TBA value of the control group and ice glazing group reach to peak value,which are 2.883 mgMDA/kg and 1.856 mgMDA/kg in turn,and then it begin to decline.2 In order to research the effect of modified atmosphere packaging on quality of frozen tilapia fillets,the indexes of hardness,pH,TVB-N value,TBA value,the relaxation time T2 and Ca²⁺-ATPase activity are measured during storage.Results indicated that the hardness,Ca²⁺-ATPase activity of the fillets show a downward trend,and TVB-N value and TBA value are rising with the extension of frozen storage time.Among all the indexes,the tilapia fillets being used vacuum packing are significantly better than the nitrogen group and the control.During frozen storage,the pH of tilapia fillets decline first and then begin to rise,the vacuum packing group has been in a better level by the slowest rate of rising.After frozen 60 d,the TVB-N value of the control group exceed national security standard,which has been the spoiled meat,and unfavorable to edible.After frozen 105 d,TVB-N value of the vacuum packing group reach to peak value,which exceed the safe level of 20 mg/100 g.What's more,it prolongs the shelf life of frozen tilapia fillets at least 45 d.LF-NMR analysis showed that the frozen tilapia fillets has three different states of water in muscle,respectively are combined water?T20?,not easily flowing water?T21?,free water?T22?.With the extension of freezing storage time,the relaxation time T21,T22 of fillets reduced constantly,especially the tilapia fillets of vacuum packaging decreased fastest.And with the matching A21 was also significantly higher than other two groups.3 Based on the single factor experiment,using L9?34?orthogonal experiment to determine the composite coating technology of tilapia fillets.Results showed that the best concentration of sodium alginate is 0.2% 0.6%,the gel time of calcium chloride is 2¹0 min,optimal concentration of chitosan is 0.1% 0.5%in the single factor experiment.Orthogonal experiments showed that best composite coating process of the frozen tilapia fillets is sodium alginate 0.2%,gel time of calcium chloride 5 min,chitosan 0.1%.4 In order to investigate the effect of vacuum packing+composite coating film agent and composite coating film agent on the quality of frozen tilapia fillets,the tilapia fillets are soaked by above two methods.At the same time,with untreated tilapia fillets as the control group.Results showed that the Ca²⁺-ATPase activity,hardness,whiteness value,water holding capacity of tilapia fillets in the storage period are in downtrend,and TVB-N value and TBA value change are on the rise.After frozen 90 days,the TVB-N value of control group rises to 20.44 mg/100 g,which exceed the safety threshold value of 20.00 mg/100 g.Meanwhile,the TVB-N value of composite coating film agent group and vacuum packing+composite coating film agent group is 18.57?18.29 mg/100 g,which still maintain freshness.Above all,the physical and chemical indicators of vacuum packing+composite coating film agent group are significantly better than the control group,but not obvious with composite coating film agent group.5 In order to study the influence of chitosan coating on the glass transition temperature?Tg?and the microstructure,the frozen tilapia fillets are used as test objects.Results showed that the microstructure of fillets treated by different processing are subject to different degree of influence in terms of fresh fillets in the condition of low temperature.Among all the fillets soaked with chitosan,0.1% chitosan solution is best to protect microstructure for tilapia fillets,0.3% chitosan solution better,and 0.7% chitosan solution is the worst.Tg analysis showed that adding chitosan can improve the Tg of tilapia fillets.The ascending range is rise first and then begin to low along with the increasing of chitosan concentration,which is favor to enhance the storage stability of fillets,basically identical with electron microscope scanning results.