Effects Of High Hydrostatic Pressure(HHP)treatment On The Quality Of Lateolabrax Japonicus During Chilled Storage And Its Antibactial Mechanism

High hydrostatic pressure?HHP?,as a cold processing method for food,is to place the food material into high-pressure vessel,which can transfer the pressure by water or oil and keep it for certain time under high pressure?100-1000 MPa?.HHP could give the formation of non-covalent bonds in food?such as hydrogen bonds,ionic bonds and hydrophobic bonds?,make the microbial death and protein denaturation in food so as to attain the goal for sterilization,enzyme-blunting,food-quality improving and shelf-life extending.Lateolabrax japonicas,one of the economic fish species in China,is famous for its fresh meat,which is rich in nutrients,full of protein for health function,and favor for consumers.However,fish tissues are susceptible to endogenous enzymes and microorganisms due to the high contents of nutrient and moisture,which caused the fish spoilage.Therefore,it is very necessary to take the appropriate treatment technology to extend its shelf life.The main contents of this paper are as follows:1.The effect of High hydrostatic pressure?HHP?treatment on the quality and structure of perch?Lateolabrax japonicas?fillets during cold storage were researched in this paper.Samples were treated with different HHP condition?0.1,200,250 and300MPa for 9 min?and then placed at 4?respectively after been washed and drained.Physiochemical?pH,hardness,Water Holding Capacity?WHC?,Low Field-Nuclear Magnetic Resonance?LF-NMR?,Thiobarbituric acid?TBA?,Total volatile basic nitrogen?TVB-N?value?,microorganisms?Total Viable Count,TVC?parameters were measured at 0,4,8,11,13,15d,the observation of appearance and microstructure were also used to evaluate the structure of Lateolabrax japonicas fillets,correlation among parameters of each group were analyzed respectively.The results show that high pressure intensity was positive correlated with the change of hardness,TBA,TVB-N,TVC value and negative correlated with pH value,WHC.The higher of pressure,the more of effects obviously.The results of LF-NMR combined with WHC also prove that the water mobility of samples and loss of free water were serious with HHP,the surface of samples were also remarkable milky and cooking-like.The results of microstructure observation for HPP illustrated that the tissue of fish muscle becomes blurred and the structure muscle fiber becomes compact disorderly,especially for 300MPa treatment.Therefore,HHP can extend the shelf life of Lateolabrax japonicus fillets during cold storage at least 4d and the optimal condition is 250MPa,9min on the whole.2.In order to study the effect of high hydrostatic pressure?HHP?with bamboo vinegar?BV?on the quality change and protein properties of perch?Lateolabrax japonicus?fillets during cold storage,HHP?250 MPa 9 min?with 0%,1%,2%,3%BV can be used for the treatment of samples respectively and then stored at 4?.Different indexes,such as sensory evaluation,physicochemical?color difference,pH value,electrical conductivity and total volatile basic nitrogen?TVB-N?value?and protein properties?actin globulin content,total sulfhydryl content,TCA soluble oligopeptide elution?,can be measured at day0,4,8,12,14,16,18 d respectively so as to evaluate the quality change and protein properties of perch?Lateolabrax japonicus?fillets during cold storage comprehensively.The results showed that the quality of samples with HPP and BV treatment could be improved its quality,The TVB-N value of samples treated by HHP with 3%BV was 31.88±1.33mgN/100g at the end of storage?18d?,which was significantly lower than that of CK group?44.77±1.89mgN/100g?.In addition that,the treatment could delay the increase of pH value and electrical conductivity,which also slow down the protein degradation significantly and maintain its good characteristics.Therefore,HHP with BV treatment can improve the quality and protein characteristics of perch fillets,HHP?250 MPa 9min?with 3%BV treatment was better than that of other groups,which can prolong the shelf life of perch fillets during cold storage for another 7 d at least.3.In order to study the effect of high hydrostatic pressure?HHP?on the changes of bacterial community structure in perch?Lateolabrax japonicus?fillets under cold storage,one of the samples were treated at 250 MPa for 9 min?HHP group?and the other one were treated at 0.1 MPa?CK group?.Then samples in two groups can be stored at 4?,total volatile basic nitrogen?TVB-N?and microbial indexes?total viable counts?TVC?,Shewanella counts,Pseudomonas counts and Psychrobacter bacteria counts?PBC??were measured at day 0,3,6,9,11,13 and 15 respectively.The correlation was analyzed at the same time so as to evaluate the effect of HHP in the quality of perch?Lateolabrax japonicus?fillets under cold storage.The bacterial community structure of perch?Lateolabrax japonicus?fillets at different storage time?early,middle,later and final stages?was carried out by high throughput sequencing technology.The results showed that the increase of TVB-N,TVC,Shewanella counts,Pseudomonas counts and PBC were significantly slower than that of control group.TVB-N value and microbial indexes can be used as freshness evaluation indexes for analyzing the quality changes of?Lateolabrax japonicus?fillets after HHP treatment.The results of high throughput sequencing indicated that the main bacteria in CK and HHP group were Bacillus sp.,Bacillus subtilis sp.and Lactococcus sp.,but the composition and type of bacteria between two groups at the later of storage were shown at the significant difference.The main bacteria of CK group in the later of storage was Pseudomonas sp.and that of HHP group was Psychobacter sp.The main bacteria of CK group in final storage was Psychobacter sp.,Pseudomonas sp.Shewanella sp.and Aeromonas sp.and that of HHP group was Psychobacter sp.,Pseudomonas sp.and Yersinia sp..HHP can inhibit the increase of TVB-N value and microbial indexes,which also have the significant effect on the bacterial composition during storage.Moreover,HHP can also significantly inhibit the growth of Psychobacter sp.and Shewanella sp..4.In order to study the dominant spoilage bacteria and their spoilage ability of Lateolabrax japonicus fillets during chilled storage at the end of storage,the specific colonies of Lateolabrax japonicus were obtained by selective mediums.The dominant spoilage bacteria were determined according to results of the selective mediums combined with sensory evaluation.The pure strains were isolated by plate streaking and the species were screened by the observation of colony morphology.The genus and species of bacteria was analyzed by physiological and biochemical experiments,16S rDNA technique.The identified dominant spoilage bacteria were inoculated on Lateolabrax japonicus with sterile treated and stored at 4?under cold storage.Total volatile base nitrogen?TVB-N?and total viable counts on different storage periods were measured respectively,TVB-N yield factor(Y_TVB-N)was used to evaluate the spoilage ability of bacteria.The results show that five strains of Pseudomonas sp were screened including P1?Pseudomonas sp.WCS374?and P2?Pseudomonas fragi P121?,P3?Pseudomonas fragi B-727?,S1?Putrefaciens Shewanella?and S2?Shewanella baltica OS185?.According to the results of spoilage capability,their order as follows:S1>S2>P2>P3>P1.The spoilage ability of P2?Pseudomonas fragi?is higher than that of P1?Pseudomonas sp.WCS374?and P3?Pseudomonas fragi B-727?,Shewanella.sp was higher than that of Pseudomonas sp..5.The aim of this study was to investigate the mechanism of high hydrostatic pressure?HHP?on the dominant spoilage bacteria in aquatic products-Shewanella putrefaciens and to understand the changes in bacterial cell damage and death.The treatment conditions were set at 200,300 and 400 MPa for 9 min respectively;samples treated by 0.1MPa were used as controlled one.Different parameters,such as survival rate,bacterial growth curve,electrical conductivity,propidium iodide?PI?intake,the content of nucleic acid and protein,enzymatic activity,were analyzed respectively.Scanning electron microscopy?SEM?can be used to observe the damage of Shewanella putrefaciens under different HPP conditions.The results showed that when compared with CK group,the growth of Shewanella putrefaciens could be greatly inhibited after different HPP treatment and the logarithmic phase of bacteria can be delayed.300MPa and 400MPa for 9 min treatments could kill all of the bacteria.Electrical conductivity and PI intake were positive correlation with the pressure,but the activity of Na⁺/K⁺-ATPase in bacterial cell membrane was significantly decreased.The results of SEM observation showed that the level of deformation and cell damage were related to the increase of pressure.HHP treatment can inhibit the growth of bacteria,destroy its structure,inactive the enzymatic activity,which led to the death of bacteria.