Characteristics Analysis Of Pseudomonas Fragi Biosurfactant And Its Effect On Microbial Community In Chilled Meat

The quality of chilled meat is strongly influenced by the composition and quantity of microorganisms present within it.Among these complex microbial communities,one or more specific spoilage organisms play a leading role in the spoilage process of chilled meat,with Pseudomonas fragi being recognized as the dominant spoilage organism.The growth and metabolism of these specific spoilage organisms are known to significantly impact the construction of the microbial community and meat quality.Biosurfactants represent a class of metabolic products secreted by microorganisms which can reduce surface tension and possess desirable emulsification,wetting,dispersion and solubilization properties.These surfactants may influence the physiological metabolic processes of microorganisms,thereby altering the construction of community.Therefore,this study aims to screen,identify,and characterize biosurfactant isolated from an isolate of P.fragi with strong spoilage potential.Subsequently,we extensively explore the influence of biosurfactant on the biological characteristics of P.fragi,as well as its role in the construction and function of microbial communities in chilled meat.The findings of this study provides valuable reference and theoretical basis for understanding the mechanism of P.fragi-mediated niche competition and structure regulation of spoilage bacteria in chilled meat.1.The ability of Pseudomonas fragi to produce biosurfactant was determined using the oil displacement method.The resulting biosurfactant was separated and extracted by acid precipitation method,and its chemical composition and physicochemical properties were subsequently determined using several analytical techniques,including Fourier-transform infrared spectroscopy and gas chromatography-mass spectrometry.The results showed that the biosurfactant predominantly comprised of amino acids,namely alanine,glycine,valine,leucine,isoleucine,proline,threonine and aspartic acid,as well as fatty acids such as hexadecenoic acid and octadecanoic acid,suggesting that the biosurfactant produced by P.fragi may be categorized as a lipopeptide biosurfactant.The critical micelle concentration of biosurfactant was found to be 100 g/L,and it exhibited surface tension-reducing properties.Moreover,the biosurfactant displayed excellent thermal stability,with only a 9% weight loss observed under conditions of 228℃.Additionally,the emulsification index of the biosurfactant for toluene,n-hexane and paraffin liquid was high,indicating that the biosurfactant was capable of effectively emulsifying different hydrocarbons.2.The effects of different concentrations of biosurfactant on the growth,biofilm formation,surface characteristics and proteolytic ability of P.fragi were studied.The results showed that the biosurfactant had a differential effect on the targeted phenotypic traits of P.fragi.Specifically,the biosurfactant demonstrated inhibitory effects on the biofilm formation,aggregation and crystal violet absorption rate of P.fragi NMC25.Conversely,the biosurfactant promoted the growth rate and enhanced the biofilm formation and aggregation of other P.fragi isolates.In addition,biosurfactant promoted the extracellular proteolytic ability of different P.fragi isolates,increasing their capacity to decompose sarcoplasmic and myofibrillar protein in a concentration-dependent manner.The results suggest that the biosurfactant has the capacity to modulate the adhesion colonization status within microbial populations and furthermore enhances the ability of the population to decompose the substrate and utilize resources in chilled meat.3.The effects of P.fragi biosurfactant on the quality and microbial community of chilled meat were studied.The spoilage status of the meat was evaluated by measuring several indicators,including total viable counts,psychrophilic microorganisms,p H,total volatile base nitrogen,and performed a comprehensive analysis of changes in the microbial community structure by employing amplified sequencing techniques.The results showed that biosurfactant inhibited the counts of psychrophilic microorganisms and the content of volatile base nitrogen in chilled meat at the end of storage,without significantly affecting the total viable counts and p H.In addition,biosurfactant promoted the proportion of Pseudomonas in the microbial community,inhibited the relative abundance of other microorganisms,and thus reduced the diversity of the microbial community in chilled meat.The results suggest that while the biosurfactant promoted the dominant position of Pseudomonas in the microbial community,it nevertheless lowered the overall spoilage ability of the community in chilled meat.