Screening And Application Of Aroma-Producing Strains From Tongcheng Dry-Cured Duck

Dry-cured duck is southern people's favorite food,because of its long storage time and rich preserved flavor.But also because of its long production cycle,high costs and being vulnerable to changes of environment,dry-cured duck is called seasonal food.Environmental microorganism has played an important role in the process of producing Tongcheng dry-cured duck.The paper selects microorganisms from dry-cured ducks to study their fermentative flavors,in order to provide research references for a novel ways of microbial fermentation technology,and the formation mechanism of Tongcheng dry-cured duck.In this paper,the physicochemical indicators and the microbial colony structure of the Tongcheng dry-cured duck were analyzed during the dry-cured duck process from Tongcheng region;By using headspace solid-phase micro-extraction and gas chromatography-mass spectrometry?HS-SPME-GC-MS?technology,we monitor the changes of volatile flavor substances in the process of producing Tongcheng dry-cured duck;by using ROAV value analysis method and comparing the key flavor compounds of Tongcheng dry-cured duck after ripening,we determine its key flavor substance and establish a sensory evaluation system.Through preliminary screening of strains,metabolizing flavor and rescreening experiments,starters of Tongcheng dry-cured duck were determined.And then,the fermentation strains were identified by nucleotide sequence alignment method of 16 S rDNA and ITS.Above all,we found out the influence of fermentation technology on the flavor of Tongcheng dry-cured dcuck.The results indicate that:?1?The pH and water activity of duck were gradually decreased.The curing process had a significant effect on pH,and air-drying process had a significant impact on water activity?P<0.05?.The overall diversity of bacteria and fungi has changed during the process of curing to air-drying.Some acid-resistant bacteria gradually become dominant strains of Tongcheng dry-cured ducks,mainly include Lactobacillus,Staphylococcus,Microbacterium,Citrobacter,Streptococcus,Acinetobacter and so on.Meanwhile,the fungis include Penicillium,Aspergillus,Creeping,etc.?2?Hexanal?1-Octen-3-ol?Nonanal are the key mutual flavor substances of the raw duck,we can see that duck flavor was significantly reduced after cured duck.And then Hexanal?Heptaldehyde?trans-2-Heptenal?2-pentylfuran?Octyl aldehyde?Nonanal??E?-non-2-enal?Octanoic acid,ethyl ester?Decenal are the key mutual flavor substances of the dried duck,which might be the flavor compounds of dried ducks.Moreover,at the end of ripening,Acetic acid,pentyl ester?Butanal?2,3-Butanedione?3-methyl-1-Butanol?3-?methylthio?-Propanal?2-Nonanone?2-Undecanone?Undecanal are the main flavor substances of the ripened duck.The unique local flavor of Tongcheng dry-cured duck includes butyraldehyde,2,3-butanedione,nonanal,2-undecanone and undecylenic aldehyde and other volatile substances,Moreover,together with the combined effect of volatile materials such as butyraldehyde,hexanal,2-heptanone,3-methyl-1-butanol,1-hexanol,1-penten-3-ol,furfural,1-octanol,and2-nonanone.?3?A non-sticky B1 strain,as amino acid deacidase negative,H₂O₂ enzyme-negative,is gained.It can degrade protein,fat and carbohydrate after preliminary screening experiment.B1 strain was identified as Lactobacillus sakei strain in method of nucleotide sequence analysis of 16 S rDNA.After preliminary screening,metabolic flavor and rescreening experiments,a mold M1 was obtained and identified as Aspergillus niger strain by ITS nucleotide sequencing analysis.The experiments selected Lactobacillus sakei strain and Aspergillus niger strain as starters.With three kinds of key flavor substances,include hexanal,nonanal and undecylenic acid,and sensory scores as indexes,were used to explore the fermentation flavor of Tongcheng dry-cured duck.Moreover,single species,fermentation temperature and fermentation time as three factors were considered.when it was inoculated with Aspergillus niger strain of 10⁷ cfu/g and Lactobacillus sakei strain of 10⁸ cfu/g,and its fermentation temperature was 20?and the fermentation time was 4 d.The key flavor components of Tongcheng dry-cured duck with the highest sensory score were best.