The Mechanism Of Volatile Compounds Formation Associated With Predominant Microbial Community In Jinhua Ham Based On AI-2/LuxS Quorum Sensing System

Jinhua ham,a traditional Chinese dry-cured ham,is prestigious for its unique quality.Flavor,which relies on microorganisms and endogenous enzymes in the ham,is the most important character to evaluate the quality and grade.Nowadays,study on ham flavor is still limited,particularly the role of microorganisms in the formation of ham and its importance have not been explored deeply.Autoinducer-2(AI-2)is related to food spoilage and fermentation process.However,there is little research on AI-2 and the formation of food flavor,and studies on how the AI-2/LuxS quorum sensing system regulates the behavior of bacteria to affect flavor are rarely reported.Therefore,we study on the mechanism of volatile compounds formation associated with predominant microbial community in Jinhua ham based on AI-2 /LuxS quorum sensing system to provide a theoretical basis for flavor formation mechanism.The main research contents include the following three parts:(1)Typical physical and chemical indexes(TVC,pH,TVB-N,TBARS)in Jinhua ham at different processing stages were detected dynamically,and it showed a rising trend as processing.The most important volatile compounds in Jinhua ham were aldehydes,and hexanal and nonaldehyde were dominant.The complexity of Jinhua ham sample and the changes of bacterial community in different processing stages were analyzed,and the dominant bacteria community was Staphylococcus spp.(2)We screened and identified Staphylococcus spp.from different processing stages of Jinhua ham.The main isolated genus was S.saparophytics by protease and lipase activity assay,and further inoculated in sterile gravy for simulated fermentation to determine the ability of producing flavor.Consequently,S.saprophyticus contributed to the formation of characteristic volatile compounds in Jinhua ham by producing hexanal,nonanal,octanal,trans-2-decenal,phenylacetaldehyde,heptanal,2-octenal,decylaldehyde,benzaldehyde.In addition,annotation of S.saparophytics genome revealed that it had genes encoding luxS,which produces the AI-2 signaling molecule,and the pathway of aldehydes synthesis of S.saprophyticus.(3)The regulation of the ability of flavor production of S.saparophytics and its mechanism were explored based on AI-2/LuxS quorum sensing system that was identified by the luxS gene and AI-2 activity.Furthermore,AI-2 had an effect on lipase and protease activities,and flavor production ability of S.saparophytics.AI-2/LuxS quorum sensing system affected the flavor production ability of S.saparophytics by regulating the aldehyde-related genes,amino acid and fatty acid metabolism pathway-related genes by looking for the receptor genes regulated by AI-2/LuxS through transcriptomics.In conclusion,the major volatile compounds in Jinhua hams were aldehydes,and the microbial characteristics of the dominant bacteria was Staphylococcus spp.during Jinhua hams processing.The S.saparophytics are related to the yields of aldehydes,indicating the contributory role of Staphylococcus in the characteristic flavor development of Jinhua ham.Furthermore,AI-2/LuxS quorum sensing system can affect the flavor production ability by regulating the aldehyde-related genes,amino acid and fatty acid metabolism pathway-related genes of S.saparophytics.Our results present an advance in the importance of microorganisms in the formation of volatile compounds in Jinhua ham.Moreover,it could provide some theoretical support for the formation mechanism of the volatile flavor of dry-cured ham and it has realistic significance in the manufacture of fermented meat products.