Research On Microflora Changes And Preservation Technology Of The Salmon Under Cold Chain

In this paper,salmon under the cold chain circulation was chosen as the research object.At first salmon quality changes under different cold chain temperature conditions were studied.Then polymerase chain reaction denaturing gradient gel electrophoresis technology,the traditional identification technology and PCR technology were used to determine the specific spoilage bacteria.After that,the modified Gompertz equation and Belehradek equation were used for fitting growth kinetic model of Pseudomonas SBW25 at different temperatures.Then single-factor test,Box-Behnken test design and response surface methodology were used to show preservation effects of complex preservatives on salmon under 4 ?;Finally,in order to provide a theoretical reference for the preservation of salmon technology,different gas ratio of modified atmosphere packaging was impacted on the salmon to find the best ratio of compound.The main contents and results were listed as follows:1.The quality changes of salmon under different cold storage temperatures were analyzed.Quality and biochemical changes of salmons stored for 12 days under super-chilled temperature(-2?)and conventional cold chain temperature(0?,4?)were measured.Sensory scores,total number of bacteria,p H value,TBA,TVB-N,color value(brightness value L and redness value a*),histamine,K value and hardness value were used to analyze the quality changes of the salmons.With the extension of storage time,the sensory scores and hardness of each experimental group were significantly declined,while the total number of bacteria,TVB-N,brightness value L,TBA,histamine and K value were rose.And the changes of pH and a* were not significantly affected by the treatment of different storage temperature,but the same trend was emerged.Upon the analysis of different index data in this experiment,salmon's quality changes could be clearly reflected by total number of bacteria,TVB-N,histamine,K value and hardness value.2.PCR-DGGE(Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis)technology,traditional technology and PCR technology were adopted to analyze the changes of microbial flora of salmon and confirm the specific spoilage organisms by testing spoilage ability of different dominant strains with yield factors.DGGE fingerprint chromatography showed that the variety of bacterial strain decreased,but bands brightness of Pseudomonas spp.and Shewanella spp.increased,which was indicated that Pseudomonas spp.and Shewanella spp.became predominant bacteria during 4 °C cold chain temperature.After separating and identifying the spoilage strains of corrupt salmon at the end of storage period,it was found that there were five strains of dominate spoilage organisms,such as Carnobacterium maltaromaticum LMA28,Pseudomonas syringe pv.syringe B728 A,Pseudomonas fluorescens SBW25,Carnobacterium sp.WN1359 and Shewanella baltica OS678.After inoculating the 5 dominate spoilage organisms into sterilized salmon and refrigerating them for a certain time,it was found that their TVB-N yield factors were 1.26,1.25,1.36,1.08 and 1.03(×10-7 mg TVB-N/CFU)respectively.This showed that Pseudomonas fluorescens SBW25 had the strongest spoilage ability on salmon,followed by Carnobacterium maltaromaticum LMA28,Pseudomonas syringe pv.syringe B728 A,Carnobacterium sp.WN1359 and Shewanella baltica OS678 successively.3.Fish meat from salmon and sterile fish sauce were chosen as growth medium of Pseudomonas fluorescence,then the modified Gompertz equation and Belehradek equation were used for fitting growth kinetic model of P.fluorescence SBW25 at different temperatures.At the same time the impact of protease activity in sterile fish juice on the kinetic parameters was explored,and the applicability of the model was evaluated.Results showed that all relative coefficient of shelf life equation led to 0.999 under the temperatures fitted by modified Gompertz equation.This means modified Gompertz equation was suitable to describe microbial growth curve of salmon and sterile fish sauce.With the temperature increasing,the maximum growth rate(?max)increased and the detention period shortened.The R2 of model between temperature and the square root of ?max and the detention period in sterile fish sauce were up to 0.9303 and 0.9887,respectively,which were much higher than that in fish meat.In sterile fish sauce,protease activity and ?max in corresponding period had similar trend in specific growth rate of growth.The degree of deviation and accuracy of equation in sterile fish sauce under different temperature were close to 1.00.Predictive growth model of SSOs based on Belehradek in sterile fish sauce could reflect the shelf-life of the salmon under different temperatures appropriately.4.In order to extend the shelf life of the salmon,single-factor test,Box-Behnken test design and response surface methodology were used to study the preservation effects of complex preservatives composed of water-soluble Rosemary extract,?-poly-l-lysine and Chitosan on salmon under 4 ? storage.The optimum ratio of each component in the complex preservatives determined by a quadratic regression model based on total volatile basic nitrogen(TVB-N)was 0.24% water soluble extracts of Rosemary,0.45% ?-poly-l-lysine and 1.0 m L/L Chitosan.Salmon was treated with the optimized complex biological preservative,then sensory valuation,the total counts of colonies,Pseudomonas and Shewanella,and physico-chemical indicators were determined to verify the effect.Results showed that interaction of ?-poly-l-lysine and Rosemary extract was the most significantly,and the least significant interactions of ?-poly-l-lysine and Chitosan,optimized complex biological preservative can significantly inhibit the growth of spoilage bacteria,and extend shelf life of the control group 8 d to14 d.5.The preservation effect of different packaging methods on the salmon at the cold chain temperature 4?,and soaked by the best ratio of compound preservative before packing was also determined.Sensory,TVB-N,K value,the number of bacteria,Pseudomonas and Shewanella were measurd to explore the optimal gas atmosphere packaging ratio.Compared with CK group,the growth of microorganisms in salmon of VP group and A,B and C were significantly inhibited,and the deterioration of sensory quality slowed.After comprehensive comparison,B group(70%CO2/30% N2)was more conducive to maintaining the salmon's high quality under cold chain,the growth rate of Pseudomonas,TVB-N content and K value were inhibited,so as to prolong the shelf life to 16 d.