Study On The Effect Of Fermenters On The Quality Of Mianning Ham

Mianning ham is a famous fermented meat product in Sichuan,which is made from the plump pig leg after dressing,pickling,washing and drying.The leg is small and generally weighs 4-6 kg,and is protected by the national geographical indication.On the basis of Penicillium lanciformis and Staphylococcus equinus screened in the previous study,this subject carried out pure breed fermentation experiments on the selected strains,and applied them in Mianning ham,and studied the changes of physical and chemical indexes,microbial diversity and flavor substances during the fermentation process.The results showed that:(1)The moisture content,aw and pH value of Mianning ham during fermentation showed a downward trend as a whole.The moisture content of the ham in the compound fermentation group was significantly lower than that in the blank control group and the single bacteria fermentation group(P<0.05).In the middle and late stages of fermentation,the pH values of all three groups of hams were significantly different(P < 0.05)and decreased to below 6.0.The salt content showed an overall increasing trend.The content of nitrite in the two groups of hams inoculated with microbial fermenters was significantly lower than that in the naturally fermented hams,and the overall trend of TBARs content increased and then decreased,both within the limits of the national standard(TBARs value ≤1 mg/kg).The protein and fat contents of the hams in the three groups at different fermentation stages increased continuously with the fermentation time,and at the late stage of fermentation,the fat content of the ham in the compound fermentation group(32.5 g/100g)was significantly higher than that of the single bacteria fermentation group(31.86 g/100g)and the blank control group(30.48 g/100g)(P <0.05).(2)High-throughput sequencing was used.The dominant bacterial phyla detected at the phylum level were Firmicutes and Proteobacteria,with the highest relative abundance of Firmicutes in the monobacterial fermentation ham(96.90%),followed by the composite fermentation group(84.35%).The dominant bacterial genera at the genus level were Staphylococcus and Cobetia,with relative abundances of 80.47% and 8.56% in the compound fermentation group,respectively.The dominant fungal phylum at the phylum level was Ascomycota,and its relative abundance was 96.31%,97.33% and 99.13% in the blank control,single fermentation and composite fermentation groups,respectively,with the highest relative abundance in the composite fermentation group.The dominant genera of fungi at the genus level were Debaryomyces,Aspergillus and Yamadazyma,with relative abundances of 55.73%,22.31% and 14.65% in the samples of the combined fermentation group,respectively.(3)Three groups of samples were examined by SPME-GC-MS technique,and 224 volatile compounds were identified in the Mianning ham samples at the fermentation maturity stage.The composite fermentation group had the largest number of volatile flavor compounds(175),followed by the monobacterial fermentation group(120).Twenty-two key flavor substances were screened using odor activity value(OAV)calculations,among which octanal,(E)-2-nonenal,(E,E)-2,4-nonadienal,hexanal,nonenal and 1-octen-3-ol contributed more in the blank control,monobacterial fermentation and compound fermentation groups of hams.Principal component analysis(PCA)was used,it was determined that 3-(methylthio)propanal,benzaldehyde,phenylethylaldehyde,decanal,undecanal,dodecanal,2-heptanone,2-nonanone,linalool,n-nonanol and 2-undecanone contributed more to the flavor of the compound fermented hams.(4)Twelve key flavor-presenting amino acids were identified among the 16 free amino acids by the TAV method.In the compound fermentation group,the largest TAV value was for glutamic acid,followed by histidine,lysine and alanine.Glutamic acid was the major freshtasting amino acid in the three ham groups,and lysine was the major sweet-tasting amino acid in the three ham groups.The bitterness of arginine and histidine contributed more to the flavor of ham in the monobacterial fermentation group,as determined from the amino acid content thermogram analysis.In the compound fermentation group,the sweetness of alanine,valine,glycine and methionine had a more prominent contribution to the ham.