Effect Of Different Freezing Methods,Storage Temperature And Thawing Methods On The Quality Of Pengze Crucian Carp(Carassius Auratus Var.Pengze)

Storage at low temperature can slow fish deterioration.Company usually uses frozen storage for the fish before producing products.The change in quality of final products will be different through different methods during freezing,storage and thawing.Pengze crucian carp(Carassius Auratus var.Pengze)of special fish in Jiangxi province was used as research object in this paper.Changes in relevant quality indicators of fresh pengze crucian carp through different freezing methods[liquid nitrogen freezing(LNF)and freezer freezing(FF)],storage at different temperature(-20?and-40?),and different thawing methods[slack water thawing(SWT),running water thawing(RWT),and low temperature and high humidity thawing(LHT)]after frozen storage were compared.Microbial structure and diversity of fresh pengze crucian carp during frozen storage were studied.This research provides theoretical guidance for establishing a set of pre-treatment processing method of pengze crucian carp.(1)The general composition of fresh pengze crucian carp muscle was determined and heat conduction formulas of pengze crucian carp back at different freezing methods and thawing methods were studied.The results shown that pengze crucian carp muscle had the largest water content and was a healthy diet food with high protein and low fat.It had high proportion of delicious amino acids,and its proportion of essential amino acids and ratio of essential amino acids to nonessential amino acids met amino acids ideal model of FAO/WHO,which indicated that pengze crucian carp was delicious and its protein belonged high-quality protein.R~2 of all fitted heat conduction formulas of fish back at different freezing methods and thawing methods was more than 0.95,indicating the rationality of these formulas.Therefore,these formulas could be used to predict the freezing and thawing time of pengze crucian carp with different back thickness through freezing methods(LNF and FF)and thawing methods(SWT,RWT,and LHT).The order of required freezing and thawing time from long to short was as follows:FF>LNF and LHT>SWT>RWT.The thinner the thickness of the fish,the faster the temperature changes.Overally temperatural changes were more balanced at LHT than those at the other two methods.(2)Changes in quality of pengze crucian carp during frozen storage at different freezing methods and storage temperature were compared.The results demonstrated that all the pH values first increased and then deceased,and the soluble myofibrillar protein(SMP)content and texture properties gradually declined with the prolonging of storage time.The thiobarbituric acid(TBA)values,total volatile basic-nitrogen(TVB-N)values,thawing loss rate,and cooking loss rate all showed an upward trend.The order of changing amount in the pH values,SMP content,TBA values,TVB-N values,thawing loss rate,cooking loss rate,and texture properties was as followed:samples during storage at-20?after FF>samples during storage at-20?after LNF>samples during storage at-40?after LNF,which indicated that LNF and storage at-40?could slow the degradation of ATP,denaturation and degradation of proteins,lipid oxidation,the loss of freezing and thawing,the decrease of texture properties,and etc.,comparing with FF and storage at-20?.(3)The results from comparison of the quality indicators of frozen pengze crucian carp through different thawing methods demonstrated that the pH values,SMP content and texture properties of pengze crucian carp decreased after freezing-thawing.The TBA values,thawing loss rate and cooking loss rate increased,as well as no significant changes in TVB-N values.It was shown that the quality of pengze crucian carp declined after freezing-thawing.was analyzed.The order of changing amount in the pH values,SMP content,TBA values,thawing loss rate,cooking loss rate,hardness,springiness,gumminess,and chewiness after different thawing methods was as followed:SWT>RWT>LHT,and the changes in TVB-N values,cohesiveness,and resilience were not obvious.The extent of ATP degradation,proteins denaturation and degradation,and lipid oxidation after LHT was less than RWT and SWT,so that the thawed sample after LHT was closed to the quality of fresh pengze crucian carp.Therefore,LHT could maintain water holding capacity of proteins and texture properties of fish muscle.(4)Changes in microbial structure and diversity of pengze crucian carp during frozen storage based on high-throughput sequencing technology were investigated.It was shown that species richness,diversity,evenness,and diversity differences with fresh fish first increased and then decreased with the prolonged storage time.The dominant microorganism transformed,and Acinetobacter was significantly suppressed in fresh samples during the middle and late period of frozen storage.During the middle period of frozen storage,the dominant microorganisms were Deinococcus,unidentified_Oxyphotobacteria,and Cetobacterium.Phyllobacterium was the dominant microorganism during the late period of frozen storage.Unidentified_Oxyphotobacteria,as the mainly dominant microorganism,existed after frozen storage,and its abundance ranks high.Spearman correlation analysis between changes in microbial community and quality indicators of pengze crucian carp during frozen storage was studied.The results demonstrated that Ralstonia_pickettii,Vibrio_ponticus,and Elizabethkingia_mening-oseptica were positively relative with SMP content,and texture property,and significantly negative with thawing loss rate and cooking loss rate.The changes in these microorganisms caused thawing loss and cooking loss by influencing the changes in SMP content,thereby declining texture properties.