Study On The Spoilage Effect Of Aeromonas On Chilled Chicken

In recent years,in order to strengthen the prevention and control of poultry epidemic diseases and improve public health safety,the promotion of chilled chicken featuring"centralized slaughter,cold chain distribution and chilled marketing"will become the main trend of poultry consumption.Chilled chicken carcass is rich in nutrients,which is an ideal medium for microbial growth and reproduction.Microbial contamination is the primary factor leading to the spoilage of chilled chicken.The shelf life of chilled chicken in the market is only 3-5 days,which seriously restricts the development of chilled chicken industry.At present,most of the researches on chicken spoilage caused by microorganisms focus on the reports of dominant spoilage bacteria,and these studies are mainly judged by the number of bacteria,while few studies on spoilage bacteria with strong ability to decompose chicken.A variety of metabolites secreted by strong putrefying bacteria destroy the cell structure of chicken,and promote nutrient leakage for the growth and utilization of autotrophic and other putrefying bacteria.It is of great significance to study the putrefying characteristics of such strong putrefying bacteria for understanding the putrefying process of chilled chicken.The previous research of our group showed that Aeromonas is the dominant spoilage bacteria in chilled chicken because of its high proportion and strong putrefaction activity.Therefore,in order to deeply understand the influence of the spoilage characteristics of Aeromonas on the spoilage process of chilled chicken,this study isolated and identified Aeromonas in chilled chicken,evaluated its spoilage ability and analyzed the difference of its spoilage ability through the evaluation of in-vitro culture phenotype and in-situ culture spoilage potential,so as to provide theoretical basis for further exploring the spoilage mechanism of Aeromonas,providing research basis for controlling dominant spoilage bacteria in chilled chicken and prolonging the shelf life of chilled chicken.The research contents and results are shown as follows:1.Isolation and Identification of Aeromonas and its RJA EvaluationAeromonas was isolated from rotten chilled chicken,and gradually identified to species level through three levels of colony morphology,biochemical identification and molecular identification.Bacterial phylogenetic trees were constructed according to 16S r DAN and gyr B housekeeping gene sequences,and the genetic relationship among the isolates was understood.Based on the ability of bacteria to decompose chicken,RJA（Raw-chicken Juice Agar,RJA）was made by ourselves,and the change of decomposition circle of Aeromonas on RJA plate was recorded,and the putrefaction ability of each strain was preliminarily evaluated.CJA（Cooked-chicken Juice Agar,CJA）analysis of cooked chicken agar medium and gelatin hydrolysis test were used to further clarify the utilization of nutrients in chilled chicken by Aeromonas.The results showed that three kinds of 12strains of Aeromonas were isolated and identified from rotten chilled chickens,including Aeromonas intermedia 13 and 16,Aeromonas salmoniliforme 25,27,29,55,27,29,J3-1,J3-2,L and Aeromonas veronii 52.RJA plate was used to preliminarily evaluate the spoilage ability of the isolates.the diameter of decomposition circle of Aeromonas salmoniliforme 29 was significantly larger than that of other isolates,showing the strongest chicken spoilage ability,followed by Aeromonas salmoniliforme 25,J3-2,27 and J3-1,Aeromonas veronii 52,Aeromonas intermedia 16,13 and Aeromonas salmoniliforme 55 had weaker spoilage ability,but salmonilified CJA analysis showed that Aeromonas could not make good use of sarcoplasmic protein and myofibrillar protein in cooked chicken after heating denaturation Gelatin hydrolysis test showed that all 12 strains of Aeromonas were gelatinase positive,which had the potential to decompose collagen in chicken.2.Evaluation of Spoilage Ability of AeromonasThe differences of spoilage ability of Aeromonas were analyzed through the evaluation of putrefaction phenotype in vitro and putrefaction potential in situ culture.The growth curves of 12 strains of Aeromonas were measured to obtain their growth law information;The results of degradation of meat protein by bacterial extracellular enzymes showed that the extracellular enzymes of Aeromonas were weak in degrading sarcoplasmic protein,and only Salmonella 25,27,29,J3-1 and J3-2 could degrade protein strips at 30 k Da,while the extracellular enzymes of Aeromonas had strong degradation ability to myofibrillar protein,and the extracellular enzymes of isolated strains could degrade myosin,actin and other corresponding strips of myofibrillar skeleton protein to varying degrees.Aeromonas salmoniliforme 29 and 57,which have similar genetic relationship but great difference in spoilage ability,were inoculated into meat for in-situ culture spoilage analysis.The results showed that the growth and reproduction ability of No.29 strain in meat was stronger,and the TVBN value and p H value of chicken samples inoculated with No.29 strain were significantly higher than those inoculated with No.57 strain,and their sensory deterioration was more serious.The quantitative analysis of spoilage ability showed that the Y_TVBN/CFUvalue of Aeromonas salmoniliforme 29 was significantly higher than 57,so Aeromonas salmoniliforme 29 had stronger spoilage ability.