The Preliminary Research Of The Separation And Aroma Produci Characteristics Of Increased Flavor Lactic Acid Bacteria Form Ghee

Ghee is a traditional dairy products in China, its production and consumption for a longhistory of thousands of years, after natural acclimation of several thousand years, some lactic acidbacteria with excellent fermentation and probiotic features were preserved, by classification,collection, this valuable resource can be protected and used. Despite the fermented dairy productsdeveloped rapidly in our country, so far almost all large dairy companies in China use foreignstarter cultures. The research in our country was fewer in terms of lactic acid bacteria, thefoundation is weak, strain character such as flavor, function can not meet the individual needs ofthe production and consumers, resulting in the homogeneity of the products. In this study, the gheeof traditional fermented as the research object, the content of acetaldehyde and diacetyl as anindex, strains with strong capacity of acetaldehyde and diacetyl production were separated, using16SrDNA analysis to determine the strain type, the aroma-producing characteristics waspreliminary studied, provide evidence for the development of new fermented dairy products.(1) By conventional separation methods, two hundred and sixteen lactic acid bacteria wereisolated from15parts ghee samples. The acetaldehyde and diacetyl content of single strainfermented milk was determinated with the method of phenol reagent spectrophotometric ando-phenylenediamine. Lactic acid bacteria were screened by using L. delbrueckii subsp. bulgaricusand S. thermophilus for the standard strains, forty-six strains of lactobacillus was isolated, sixstrains with strong ability to produce diacetyl and forty-one strains with strong capacity to produceacetaldehyde，the production capabilities of acetaldehyde and diacetyl of R128was strong.Through16SrDNA analysis, the strains were determined to E.durans, E.faecalis, S.agalactia andL. plantarum.(2) Through the study, the optimum inoculum density of various strains were different toproduce acetaldehyde and diacetyl, it was between4%~8%. The diacetyl content of various strainswas higher with citrate addition amount of0.5%~2%. In the process of fermentation, pH valuedecreased with time, the enzyme activity increased at first then decreased along with time, thecontent of acetaldehyde increased first and then decreased with the extension of time, diacetylcontent always increased with the time prolonging. Correlation analysis was conducted betweenthe value of pH, activity of lipase and protease, the amount of acetaldehyde and diacetyl of strains,effect of the pH and enzyme activity of acetaldehyde and diacetyl content was studied, themechanism of strain produce acetaldehyde and diacetyl was preliminary explored. The pH aresignificantly negative correlated to the content of acetaldehyde and diacetyl, and lipase andprotease activity was positively correlated to the content of acetaldehyde and diacetyl.(3) Pure fermented yoghurt samples and mixed fermented yoghurt samples were detected byelectronic nose, and the data were processed by principal component analysis (PCA). In the fourpure fermented yogurt samples, the original response curve and odor fingerprints of yoghurtsamples fermented by R29, R93, R128had a high degree of similarity, the flavor composition of R29, R93, R128was similar, the original response curve and odor fingerprints of R61hadsignificant differences with other samples. In the five mixed strain fermented yogurt samples, theoriginal response curve was similar, the blank were well separated by PCA, the response values ofyogurt samples were significantly increased compared with blank form odor fingerprints, thecontent of sulfides, pyrazine, furan, esters, aldehydes, ketones and hydrocarbons of yogurtsamples were higher then blank samples.