| Yellow catfish(Pelteobagrus fulvidraco)takes an important share in the freshwater fish product consumption market of China,with an annual output of500,000 tons in 2018.However,due to the strong hard spines of the pectoral fin and dorsal fin of yellow catfish,joint locking occurs during stress,and the fish are easy to stab each other in the process of fishing and transportation,leading to infection and death of fish,consumers are also vulnerable to injured during the slaughter.In addition,with the current urbanization and popularization of the Internet of Things,more and more consumers choose online retail and cold chain logistics to buy fish products.Therefore,it is a better way to sell yellow catfish after slaughter.However,there is a high moisture in the muscle of yellow catfish,lipid oxidation and spoilage will occurs with the actions of endogenousenzymes,exogenous enzymes and microorganisms after slaughter,which will affects the muscle quality and food safety.Therefore,in this paper,the changes of quality,nutrients and microorganisms in the cold preservation process after slaughted yellow catfish were studied.The purpose of this paper is to provide reference for cold chain transportation and logistics distribution.Three temperature groups T1,T2 and T3 were designed(33 ℃,27 ℃,15 ℃)to simulate the average temperature in different seasons of Chongqing,each group was cold-preserved to(0,2,4,6,12 h hours)respectively,and two treatment groups were set up at each preserved time point.The slaughtered yellow catfish around total weight of 1kg per group,were placed in a foam insulation box(40*20*19cm,foam thickness2.5cm)with 10 biological ice packs which avarege weight is 267 grams and frozen at-20℃ refrigerators for 48 h,and then cold-prserved for 12 h,all yellow catfish samples were divided equally into five parallel groups.Sampling muscles at different time points,physical indicators of samples were measured by texture analyzer,WHC(water holding capacity)and WBC(water binding capacity)were tested.Then,use national standard were used to evaluated the values of p H,volatile base nitogen(TVB-N),metmyoglobin(Met Mb),2-thiobarbituric acid(TBA),and four nutrient components(moisture,crude protein,crude fat,crude ash),Moreover,acid hydrolysis method was used to determinated the contents of amino acids,fatty acids contents were detected by high efficiency gas chromatograph,Afterwards,the variations of microbial diversity of samples were determined by the 16 S r RNA high-throughput sequencing.Based on the above parameters,the muscle quality,nutritions,microbial diversity changes of slaughtered yellow catfish within cold preservation process were comprehensively analyzed and assessed.The main results are as follows:(1)Effects of cold preservation on muscle quality of yellow catfish.The results showed that the values of hardness,springiness,cohesiveness,gumminess,resilience and chewiness of yellow catfish muscle by cold preservation at different environmental temperatures were decreased with the extension of preservation time,and the higher preservation temperature,the lower texture indexes value.After 12 h of preservation,the decrease of hardness was 277.73 g in T1 group,springiness and cohesiveness in T1 group decreased from 0.545 to 0.478 and 0.38 to 0.315 respectively.However,the change of texture indexes were small in T2 and T3 group,the hardness of T2 and T3 group decreased from 1148.04 g to 927.42 g and 946.76 g respectively,the decrease of springiness were 0.072 and 0.041 respectively,and the decrease of cohesiveness were0.054 and 0.045 respectively.Comparing with 0h control,there were significant decreases in the texture indexs of yellow catfish muscle in T1 group after preserved 6h(p<0.05),but there were significant decreases in the texture indexs in T2 and T3 group after preserved 12h(p<0.05).After 12 h of cold preservation,the value of each texture index in T1 group was significantly lower than that in T3 group.The results showed that the lower the temperature is,the better the muscle quality will be.The change trend of water holding capacity(WHC)is the same as that of texture.The WHC of T1,T2 and T3 group decreased from 75.05% to 65.59%,68.92% and 71.79% respectively.The index of water binding capacity(WBC),muscle cooking loss rate,storaged loss rate,and frozen leakage rate all increased after the preservation,and the preservation temperature was higher,the greater to the loss rate.Tested the physical and chemical indexes,showed that the values of p H,volatile base nitogen(TVB-N),metmyoglobin(Met Mb)and 2-thiobarbituric acid(TBA)values increased gradually with the extension of preservation time,but the changes were small.After 12 h of preservation,the p H of the muscle in T1,T2 and T3 group were 6.94,6.96 and 6.96 respectively,indicating no rancidity.In the T1 group,the content of TVB-N increased from 12.64mg/100 g to 18.19 mg/100 g after 12 h of cold preservation,but the value did not exceed the maximum content of national standard(20 mg/100g).After 12 h of preservation,the content of TVB-N in the muscles of the T2 and T3 group were slightly higher than that before preserved,but not significantly different with that before preserved(p>0.05),and the contents of TVB-N in the muscle samples of the T2 and T3 group were not exceed the first-grade freshness.The results showed that the lower the cold preservation temperature was,the better preserved,and the higher the freshness of yellow catfish.(2)Effects of cold preservation on muscle nutritional components of yellow catfish.The results showed that 17 kinds of amino acid and 13 kinds of fatty acid were detected in the muscles of yellow catfish after 6h of cold preservation at different environmental temperatures.The total amino acid mass fraction of muscle was as high as 79.17%,the essential amino acid mass fraction of T1＿6 was highest(33.02%),and the highest sum of eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA)was5.96%.The mass fraction of each amino acid of yellow catfish was slightly increased with the extension of preservation time at the same temperature,but the difference was not significant(p>0.05).The trends of mass fraction of the most fatty acids were similar to that of amino acids,which gradually increased with extension of preservation time(p>0.05).At 0h,the moisture in muscle was 79.48%,moisture in T1 group slightly increased after 12 h of preservation(80.84%)(p>0.05),while that of the samples in other groups decreased gradually(78.82% and 78.63%,respectively).The trend of content of crude ash and crude fat was similar to that of moisture,with no significantly change after preservation,while the contents of crude protein in the yellow catfish’s muscles increased after preserved 12 hours in the T1,T2 and T3 group(79.78%,79.51% and 79.74% respectively).(3)Effects of cold preservation on muscle microbial diversity of yellow catfish.The results showed that,at the same environmental temperature,the total number of microorganisms decreased first and then increased with the extension of preservation time.After preservated 6h,the total number of microorganisms in T3 group was 1704,higher than that in T1 and T2 group(916 and 345 respectively),indicated that genus Acinetobacter and other psychrophiles bacteria were the majority in the colony of muscle.There were 22 species microorganism in the muscle at 0h,which the species abundance is all more than 0.01,that was higher than that of 2h,4h,6h in T1,T2 and T3 group.The number of the most advantage microorganism in T1 group are more than that in T2 and T3 group,the results show that the decrease of cold preservation temperature results in the slow growth and even death of some non-psychrophiles or non-dominant microorganisms,reduced the microbial diversities.The results showed that low cold preservation temperature is conducive to slow down the deterioration of muscle.In order to ensure the high quality of muscles,considering the change degree of quality parameters in cold preservation of yellow catfish after slaughtered.Therefore,after slaughtered,yellow catfish should not be kept for more than 6 hours under the environmental temperature of 33℃ and the above experimental conditions.However,the yellow fish after slaughtered could preserved 12 hours at the environmental temperature of 27℃ and 15℃.This study will provide a reference for the cold chain logistics and transportation of yellow catfish,and provide basic data for the cold-preserved,processing and qualitysafety of aquatic products. |
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