| Grass carp is a traditional food in China,and its processing method is usually cured.However,the traditional curing method is affected by climate and environment factors,also,too much salt is added,which can not guarantee the quality of fish products and seriously affect people's health.The paper has taked grass carp fillet as the research object,which studied the effects of controlled freezing-point impregnation,controlled freezing-point dehydration and controlled freezing-point storage on the controlled freezing-point characteristics of grass carp fillet with low salt and high moisture content.On this basis,the changes of quality,freshness and microflora of grass carp fillet were further analyzed.In addition,low-temperature lactic acid bacteria in grass carp fillet were isolated,screened and identified.The main research contents are as follows:1?The controlled freezing-point characteristics of grass carp fillets were analyzed based on the combination of salt leaching and controlled freezing-point dehydration:Grass carp fillets were impregnated with 0%,2%,4%,6%and 8%salt water,then dehydrated to70%+1%,60%+1%,50%+1%,40%+1%water content under controlled freezing-point and vacuum.The freezing point,salt content,volatile base nitrogen and texture characteristics of grass carp fillets were analyzed.The results revealed that it was suitable to immerse the grass fillets for 10 h.The same salt water was used to impregnate the grass fillets,the lower the controlled freezing-point dehydration rate was,the lower the freezing point of the fish fillets was.The dehydration rate was the same,the higher the salt water concentration was,the lower the freezing point of the fish fillets was.The freezing point of 8%salt content can be reduced to-12.23 °C.The TVBN values of grass carp slices were slightly improved in the two treatments,and the effects on the freshness and texture of grass carp chips were not significant.2?Effect of Storage Temperature on Ice Preservation of Grass Fillets:In order toprolong the controlled freezing-point storage period of grass carp fillets,salt soaking and vacuum dehydration at controlled freezing-point were used to reduce the freezing point of fish in the experiment,thereby reducing the t3?emperature of the controlled freezing-point storage.In the experiment,fresh grass carp fillets were immersed in 4%saline for 10 hours,then dehydrated to 60±1%water content(freezing point was-4.2 ?)by controlled freezing-point and vacuum.Two groups of controlled freezing-point groups were set,the storage temperature of group T1 was set to(-0.5±0.5)?and the storage temperature of group T2 was set to(-3.5±0.5)?,the CT of refrigerated group at 4?was used as control.The p H value,total number of colonies(TBC),thiobarbituric acid value(TBA),free amino acids,volatile base nitrogen(TVBN)and corresponding sensory evaluation were periodically measured during storage to explore the effect of storage temperature on the quality change of grass carp fillets.The results revealed that reducing the storage temperature by reducing the freezing point can slow down the rising rate of TBC,TBA and TVBN,prolong the storage period significantly,and promote the production of free amino acids and enhance the taste of grass carp fillets.The storage period of samples stored at-0.5 ?and-3.5 ?on controlled freezing-point was 50 d and 60 d,respectively,and the storage period of refrigerated samples was only 30 d.According to the comprehensive analysis,the grass carp fillets stored at-3.5 ?had the best preservation effect,and the sensory was the best,followed by-0.5 ?.3 ?Analysis of Diversity of Grass Carp Fillets Stored at Different controlled freezing-points Based on High-throughput Sequencing:In order to investigate the changes of microbial flora in grass carp slices under different controlled freezing-point storage temperatures.In this experiment,fresh grass fillets(with a freezing point of-1.1 ?)and grass carp slices adjusted by freezing point(with a freezing point of-4.2 ?)were used as the research object and stored in group A(-0.5 ± 0.5)? and group B(-3.5±0.5)?,respectively.Firstly,the changes of volatile basic nitrogen(TVBN)and total bacterial count(TBC)of two groups of grass carp fillets were analyzed,and then the microorganisms in grass carp fillets were analyzed by high throughput sequencing.The changes of bacterial flora in two groups of samples at different storage stages were obtained.The experimental results show that with the increase of storage time,the TVBN value and TBC increase gradually.The comprehensive analyses showed that the storageperiod of the group A was about 18 d,while the storage period of the group B was about 60 d.At the phylum level,group A was mainly Proteobacteria and Bacteroides,while Group B has an absolute advantage in the early stage of Proteobacteria,and in the later stage,the Firmicutes is the main.At the generic level,Acinetobacter,Aeromonas and Flavobacter were the dominant genera in group A at the early storage stage,and the relative abundance of Acinetobacter reached the highest value of 50.74%at the end of storage.The main dominant bacteria in group B were Acinetobacter and Aeromonas at the early stage of storage.At the end of storage,Staphylococcus had an absolute advantage,accounting for 30.33%.4?Preliminary Isolation,Screening and Growth Characteristics of Low Temperature Lactic Acid Bacteria:Lactic acid bacteria have strong growth ability and can produce bacteriocin,and bacteriocin has an inhibitory effect on bacteria.In this chapter,in order to carry out preliminary separation and screening on low-temperature lactic acid bacteria,the physiological and biochemical characteristics and growth performance of the strains were studied by traditional isolation combined with 16 S r DNA identification.The results revealed that L1 strain was a low-temperature lactic acid bacteria,it grew well at low temperature,it also had strong NaCl tolerance and acid production ability. |
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