Analysis Of Flavor Compounds And Three Ester Metabolic Enzyme Genes Of Food-borne Yeast Isolates

12 food-borne yeast isolates were studied in the work, collected from 5 different areas including Tianjin, Ningxia, Xinjiang, Xizang and Inner Mongolia. The isolates were identified by phenotypic characteristics and analysis of 26S rDNA gene D1/D2 domain sequences. They were proved to be Saccharomyces cerevisiae (3 isolates), Torulaspora delbrueckii (2 isolates), Pichia kudriavzevii (2 isolates), Pichia cactophila (1 isolate), Kluyveromyces marxianus (1 isolate), Clavispora lusitaniae (1 isolate), Kluyveromyces marxianus (1 isolate) and a suspected new species S4. The results obtained demonstrated the complexity of yeasts in the food.SPME-GC-MS was used to analysis and discuss the flavor compounds of fermentation liquid by different yeast isolates. Pure wort medium was selected as fermentation substrate in the study, with which the detecting result showed optimal kinds and contents of flavor compounds, including esters, alcohols and acids. The result revealed metabolic characteristics of flavor compounds in yeasts. Different kinds and contents of flavor compounds were detected from fermentation medium by different strains, while minor difference was observed in the same species. In particular, flavor compounds were identified in wort medium with strong aroma by S. cerevisiae A1. Among these compounds, most of them were esters, such as ethyl acetate, ethyl caprotate, ethyl caprylate and ethyl caprate.Three ester metabolic enzyme genes were cloned from S. cerevisiae A1, including EHT1, EEB1 and TGL3 with Genbank number GU471248, GU471249 and GU471250, respectively. The sequences showed a high degree (>99.7%) of homology to those repored in Genbank. Sequence alignment indicted that EHT1 and EEB1 were genes encoding alcohol acyl transferase, which were responsible for medium-chain fatty acid ethyl ester biosynthesis during fermentation, and TGL3 was a triacylglycerol lipase gene, playing major part in TAG mobilization from lipid particles. Distribution of the three genes in different yeast isolates was studied with PCR method in the work. In total of 15 yeast strains, EHT1 was detected in 12/15; EEB1 was detected in 4/15; TGL3 was detected in 5/15. The result obtained demostrated the relationship between yeast and the three ester metabolic enzyme genes, providing possible reference in industrial yeast identification.