Medium-chain volatile flavour esters are important molecules since they have extensive applications in food, fragrance, cosmetic, paint and coating industries, which determine different characteristics of aroma or taste in commercial products. Biosynthesis of these compounds by alcoholysis is catalyzed by acyl-CoA:ethanol O-acyltransferases Eht1 or Eeb1 in Saccharomyces cerevisiae. In this study, these two yeast enzymes were selected to explore their preparations as the form of whole cell biocatalysts for the production of volatile flavour esters. Here, the novel whole cell biocatalysts Pichia pastoris yeasts with functional extracellular expression of Eht1 or Eeb1 were constructed. Flavour production was established through an integrated process with coupled enzyme formation and ester biosynthesis in the recombinant yeasts in one pot, leading to the formation of volatile C6–C14 methyl and ethyl esters from wort medium. Interestingly, there is no significant difference between P. pastoris-EHT1 and P. pastoris-EEB1 in substrate preference during flavour biosynthesis, indicating a similar role of Eht1 and Eeb1 in P. pastoris cells, in contradiction with previous findings in S. cerevisiae to some extent. Consequently the study not only provides a greater understanding of these two enzymes in a heterogeneous host, but also demonstrated the positive effect of the recombinant Eht1 and Eeb1 in ester formation by P. pastoris live cells, potentially paving the way towards achieving efficient production of volatile flavour by an integrated biocatalytic system composed of recombinant enzyme production and flavour biosynthesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1195-0) contains supplementary material, which is available to authorized users.

Sequence analysis of DIID2 region of 26S rDNA was used for identification of different yeasts isolated from food-borne material. Then, their aromas compounds were detected and analyzed by SPME-GC-MS, another biology information technology.12 yeast strains were grouped in 7 species belonging to 5 genera as follows: Saccharomyces cereVISlae, Torulaspora delbrueckii, Kluyveromyces marx ian us, Pichia cactophila, Clavispora lusitaniae, Pichia membranifaciens, and Pichia kudriavzevii. Among all yeast strains, most of volatiles were similar, but contents were affected by different strains. Strain Al (Saccharomyces cerevisiae) produced relatively higher aromas compounds than S6 (Kluyveromyces marxianus). The result of GC-MS showed ethyl octanoate and phenylethyl acetate were high-impact flavors by strain Al and S6, respectively. In conclusion, it is a reliable identification system to indentify food-borne yeasts at species level using 26S rDNA sequencing and phenotypic studies. SPME-GC/MS analysis highlights aroma compounds can be used for pre screening potential edible yeast strains effectively.