Investigations on the biotechnological production of natural isoamyl acetate and ethyl acetate

In this study, the production of isoamyl acetate using Williopsis saturnus from sugarbeet molasses by fermentation and from fusel oil in a molasses based medium by bioconversin; and the production of ethyl acetate using Pichia yeasts by fermentation were studied. For isoamyl acetate production the effects of 3 different strains of Williopsis saturnus (HUT 7087, IAM 12217 and NCYC 22), temperature (15 ºC and 25 ºC) and aeration (aerated, semi-aerated and unaerated) on the production of isoamyl acetate were determined and enhancement of isoamyl acetate production by bioconversion with addition of fusel oil at the most suitable conditions was aimed. For ethyl acetate production, the influence of 2 different yeasts (Pichia anomala NCYC 432 and Pichia subpelliculosa NCYC 436), temperature (15 ºC and 25 ºC) and aeration (aerated, semi-aerated and unaerated) were examined.Fermentation and bioconversion trials were performed with batch fermentors at controlled conditions and with orbital shaker in flasks, respectively. Flavour compunds were determined with gas chromatography-flame ionization detector.According to the results obtained, Williopsis saturnus HUT 7087 was the highest isoamyl acetate producer among Williopsis saturnus strains, and that strain formed higher amount of ester at 25 ºC than at 15 ºC, at semi-aerated medium than aerated and unaerated mediums. The addition of 1% of fusel oil into medium caused a 3 fold increase in isoamyl acetate production and the maximum amount of isoamyl acetate produced was 354 mg/L. Pichia anomala NCYC 432 produced higher level of ethyl acetate than that of Pichia subpelliculosa NCYC 436 from molasses. The highest amount of ethyl acetate was determined at 25 ºC than at 15 ºC, at semi-aerated medium than aerated and unaerated mediums, and the maximum amount was found about 6.7 g/L.Keywords: Natural flavour, Williopsis saturnus, Pichia, fermentation, bioconversion