Study On The Spoilage Effects Of Specific Spoilage Organisms Pseudomonas Koreensis PS1 And Bacillus Fusiformis J4

Microbial infection is one of the most important factors causing pork spoilage.Quorum sensing is a mechanism for bacteria to communicate information by secreting chemicals called signal molecules,which may be connected with food spoilage.Therefore,the growth and substrate consumption kinetics of Pseudomonas koreensis PS1 and Bacillus fusiformis J4,specific spoilage organisms(SSO)isolated from chilled pork,were studied during pork gravy culture at 4?.The effects of the main medium composition and culture conditions on the secretion of N-acyl-homoserine lactone(AHLs)by SSO were further investigated,and analyzed the effects of exogenous AHLs signaling molecules on the SSO spoilage.The main results are shown as follows:1.Study on the growth and substrate consumption of SSO in pork gravy.In the experiment,SSO were back-incorporated into fresh broth and stored at 4?for deteriorate,during which samples were taken to determine the growth of the bacteria and the substrate consumption.It was shown that two SSO were able to grow in broth at 4?,and P.koreensis PS1 was more capable of breaking down proteins and carbohydrates than B.fusiformis J4.The TVB-N content produced by P.koreensis PS1 was as high as 31.62mg/100 m L by the 9th day of incubation,and further calculation of TVB-N yield factor for SSO confirmed that P.koreensis PS1 had a stronger spoilage capacity.The kinetic analysis showed that the growth of two SSO in the broth conformed extremely to the modified Gompertz equation,and the consumption of proteins and sugars by SSO conformed to the exponential equation.2.Study on the effects of the medium main composition and culture conditions on the production of AHLs signaling molecules by SSO.The types and patterns of secreted signaling molecules of SSO were analyzed by biosensing and?-galactosidase activity methods,investigated the effects of the medium main composition,the culture conditions and exogenous addition of S-adenosyl methionine(SAM)on the secretion of AHLs by SSO.The results showed that P.koreensis PS1 could secrete AHLs-type signaling molecules,while B.fusiformis J4 could not.The AHLs concentration enhanced as the bacteria number increases,and its peak appeared at 16th hour.The main components of the medium had different degrees of AHLs,and the greatest amount of AHLs was secreted when fructose was used as the carbon source.Similarly,the secretion of AHLs was greatest when ammonium chloride was used as the nitrogen source.An increase in the concentration of casein-hydrolyzed amino acids reduced the secretion capacity of AHLs,and 5%Na Cl greatly inhibited the secretion of AHLs.The culture conditions also affected the secretion of AHLs.The ability of P.koreensis PS1 to secrete was reduced under weak acid and alkaline.The optimal temperature for AHLs secretion was 28?.In addition,excessive inoculum size and high shaker speed reduced the ability of P.koreensis PS1 to secrete AHLs.32?mol/L SAM enhanced the utilization of reducing sugars and total phosphorus by P.koreensis PS1 without affecting bacterium growth,and obviously promoted the AHLs secretion.3.Study on the effects of exogenous AHLs signal molecules on the SSO spoilage.Exogenous addition of AHLs was used to analyze their effects on the growth and spoilage factors of SSO in liquid culture,and then the effect of C6-HSL on SSO spoilage in chilled pork was evaluated.The results showed that there were significant differences in the effects of different types AHLs on the spoilage factors of SSO.C₆-HSL remarkably promoted the protease activity,lipase activity and the biofilm formation of P.koreensis PS1.50?mol/L C₆-HSL extremely significantly promoted the growth of P.koreensis PS1,while changing the AHLs types had no effect on growth.10?mol/L C₆-HSL increased the lipase and trypsin activities of P.koreensis PS1 during the storage of chilled pork at 4?,accelerating the decomposition of proteins,fats and carbohydrates,resulting in a significant expansion in TVB-N,putrescine,tyramine and cadaverine.Unexpectedly,C₆-HSL had little effect on the spoilage of B.fusiformis J4.This experiment investigates the mechanism of spoilage effect of SSO on chilled pork,which has an important theoretical basis and practical significance for preservation of chilled pork and its meat products.