Effects Of Slurry Ice Treatments On The Quality And Microbial Community Change Of Lateolabrax Japonicas During Circulation

Lateolabrax japonicusare is one of the most common economic fishes,and is also one of the most important species in China.It mainly distributed in China offshore and estuary seawater,fresh water interchange,which is one of the high-grade freshwater fish species in China due to its delicious taste,high protein,vitamins and essential amino acids.However,due to the weakness of muscle tissue,Lateolabrax japonicus is vulnerable to the effects of microorganism,fat oxidation and endogenous enzymein in the circulation after catched,which results in spoilage and deterioration of the fish muscle,and reduces the nutritional value.Ice storage d is a commonly used technology for the preservation of aquatic products,which can inhibit the activity of enzyme and the growth of microorganisms in fish.Slurry ice is a new type of fresh-keeping technology.Due to the advantages of small and smooth ice particles,good fluidity and high latent heat value,slurry ice can completely immerse the fish body in storage stage,effectively insulate oxygen,and reduce the mechanical damage on the surface of the fish body at the same time.In this paper,five parts of research on Lateolabrax japonicus preservation were carried on in order to improve the quality of Lateolabrax japonicus during ice storage.The main research contents and conclusions are as follows:1.First,the effects of slurry ice(SI)and acidic electrolyzed water ice(AEWI)and crushed ice on the quality,ATP-related compounds and microorganism changes of Lateolabrax japonicus during storagewere investigated in order to find an effective method for keeping Lateolabrax japonicus.The effects of slurry ice(SI)and acidic electrolyzed water ice(AEWI)on the quality,ATP-related compounds and microorganism changes of Lateolabrax japonicus during ice storage,thesamples were treated by slurry ice(SI)and acidic electrolyzed water ice(AEWI)respectively,and crush ice as the controlled(CK).The sensory,Total volatile basis nitrogen(TVB-N),Texture Profile Analysis(TPA),ATP degradation(K,H,Fr value)and Microbiological(Total Viable Counts(TVC),Pseudomonas counts,shewanella counts)parameterswere analyzed..The results indicated that samples treated with SI and AEWI could be kept the better sensory quality,delayed the decomposition rate of muscle tissue at the late storage.Meanwhile TVB-N value,K value,TVC,Pseudomonas counts and shewanella counts in samples of SI and AEWI could be inhibited significantly.In addition,the content of Adenosine Triphosphate(ATP)and Inosine Monphosphate(IMP)were decreased,Hypoxanthine nucleotide(HxR)was increased at first and then decreased,Hypoxanthine(Hx)was accumulated with the extension of storage time.The inhibiting effect of SI on the degradation process of ATP was more significant than AEWI one.The results of correlation analysis and Principal Component Analysis(PCA)showed that the growth of microorganism was closely related with TPA,IMP,HxR and Hx,which could represent the freshness variation of Lateolabrax japonicus during ice storage.Therefore,the use of SI and AEWI could replace crushed iceand prolong shelf life of samples greatly;slurry ice has the best preservation effect especially.2.Seconed,the effects of different ice treatments on bacterial composition and its metabolic function in Lateolabrax japonicuswere analysised by using High-throughput Sequencing.The variation of microorganisms and the correlation between bacterial flora change and quality index in Lateolabrax japonicuswere investigated.Samples were treated with slurry ice(SI),acidic electrolyzed water ice(AEWI)and crushed ice(CK)respectively.Total volatile basic nitrogen(TVB-N)and K value of samples with different treatments during ice storage were measured;the bacterial composition and its metabolic function were also analyzed by using high-throughput sequencing and phylogenetic investigation of communities by reconstruction of unobserved states(PICRUSt).The results showed that SI andAEWI had certain fresh-keeping effect on samples,the effect of slurry ice for inhibiting the degradation rate of protein and nucleotide in Lateolabrax japonicus was most significant.The result of high-throughput sequencing showed that,Bacillus,Lactococcus and Oceanobacilluswere the main dominant bacteria at the early stage of storage(0-3d)in all samples,the relative abundance of these dominant bacteria in CK and AEWI groups were much higher than that in SI.In the middle and later periods of storage(12-21d),the relative abundance of Pseudomonas andShewanellain SI wereincreased from 1.25%,0.03%to 4.38%,5.4%,and Moritella,Shigella,Aliivibriowere also increased rapidly,which have a significant impact on the deterioration of Lateolabrax japonicas.The relative abundance of Acinetobacter was at the highest proportion,which was up to 27.77%in sample of CK and became the dominant spoilage bacteria.However,in AEWI group,Pseudomonas and Acinetobacterwere not detected at the early stage.At day 21,the increase of relative abundance in Pseudomonas and Acinetobacter had accelerated the corruption of samples.Pseudomonas,Acinetobacter,Psychrobacter and Shewanella were positively correlated with TVB-N and K values of samples,which may were the specific spoilage organism(SSO)of Lateolabrax japonicas during ice storage.When compared with the other two groups,SI can inhibit the degradation rate of protein and nucleotide in samples effectively.The relative abundance of genes was related to amino acids,lipid and carbohydrate metabolism in samples were greatly higher than that in SI at the later storage period(P<0.05).This may partially explain the reason why SI could delay the spoilage at the level of bacterial metabolism,which could provide the reference for optimizing the fresh-keeping methods of Lateolabrax japonicas.3.In the third part,the effects of precooling treatment with slurry ice on the quality change of Lateolabrax japonicas during circulation were studied.The circulation of Lateolabrax japonicas was simulated and the effect of precooling treatment with slurry ice on the quality change of fresh Lateolabrax japonicas during circulation was researched.Different treatments,such as continuousslurry ice(SI)and crushed ice(CK)precooling,transportation and storage,slurry ice precooling-no ice-crushed ice(SNI),were used for Lateolabrax japonicas respectively after samples were divided randomly.Sensory evaluation,physiochemical(pH,salinity,TPA,and Thiobarbituric acid(TBA)),microbial(TVC)parameters combine with scanning electron microscope(SEM)and sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE),were measured at regular intervals.It showed that the chilling to 0?of samplesin slurry ice in 1-1.5h,and the terminal temperature was-1.1?.The cooling rate is significantly higher than that of crushed ice.As for its quality,the advantage of continuous precooling in slurry ice can be observed during the later storage.When compared with the CK group,the increase of pH value,TBA value and TVC of Lateolabrax japonicas in SI storage can be slowed down significantly.Moreover,the degradation of protein and muscle tissue was also inhibited;the shelf-life of SI group can be extented from 12d to 18d.The core tenperature of Lateolabrax japonicas in SNI group were under 0.8?during transportation without ice,it showed that slurry ice can control the temperature fluctuation of Lateolabrax japonicaseffectively.The quality change of Lateolabrax japonicas in SNI group has no significant difference with that in CK group,and the shelf-life all were 12d.Therefore,slurry ice was one of the rapid and efficient methods for preservation of aquatic product,the method of transportation without ice has a good guidance in short-distance transportation of aquatic products.4.In the fourth part,slurry iceand cold storage were used to simulate the actual circulating temperature of Lateolabrax japonicus,and the growth kinetics of spoilage organisms and the prediction of shelf life for samples were discussed.The circulation of Lateolabrax japonicus was simulated by different storage conditions,such as slurry ice storage(-1.8?),crushed ice storage(0?),cold storage one(4?)and cold storage two(10?).The kinetic growth of total viable counts,shewanellacounts and Pseudomonas counts,TVB-N and QI(Quality index)value at the end of the shelf lifewere analyzed respectively.On the basis of the dynamic change of SSO with modified Gompertz equation,Belehradek equations and Arrhenius equations were used to construct the prediction models of growth and shelf life for SSO.The results showed that the modified Gompertz equation could describe the dynamic microbial growth in Lateolabrax japonicus at different storage conditions and the average minimum corruption values ofshewanella counts and Pseudomonas counts were6.48±0.41lg(CFU/g),6.33±0.36lg(CFU/g)respectively.Meanwhile,the applicability of models were validated under crush ice storage(0?)and temperature-fluctuation conditions(slurry ice precooling(-1.8?)–transportation without ice(0.8?)–crush ice(0?).The bias factors(B_f)and accuracy factors(A_f)of shewanella counts and Pseudomonas counts from the models based on Belehradek equations were 0.9936,0.9510 and 1.0242,0.9821and 1.0845,1.0425,1.1075,1.0934 respectively and the relative errors of shelf life model were within the range of 0-10%.The accuracy of Belehradek equation was better than Arrhenius equation.In conclusion,the models obtained by Belehradek equations were more effective for predicting the growth of SSO and the shelf life of samples at different storage conditions so as to provide the theoretical basis for predicting the shelf life of Lateolabrax japonicus.5.The last part studied the effect of slurry ice combined with antioxidant of bamboo(AOB)and rosemary extract(RE)on the antioxidant activity and microorganismduring storage.The effects of antioxidant of bamboo(AOB)slurry ice and rosemary extract(RE)slurry ice on the antioxidant activity and microorganism of Lateolabrax japonicas during storage were studied.The samples treated with slurry ice were used as control group(SI),0.1%AOB+SI(AOB-SI)and 0.1%RE+SI(RE-SI)were used for the storage of Lateolabrax japonicas respectively.Sensory score,total viable counts,Peroxide Value(POV),malondialdehyde(MDA),free fatty acid(FFA)and protein oxidation(carbonyl value,Sulfhydryl value)were measured respectively during stoage.The results showed that samples with AOB-SI and RE-SI treatment could delay the increase of POV,MDA and FFA content significantly,inhibit the content of carbonyl,sulfhydryl and TVC greatly.The antioxidant effect of AOB-SI treatment was slightly better than that of RE-SI.It can be seen that AOB-SI and RE-SI can delay the process of hydrolysis and protein oxidation,inhibit the growth of microbes,which can prolong the shelf life of Lateolabrax japonicas with slurry ice for another 3d.