Produção de fenóis voláteis por isolados de Dekkera bruxellensis da fermentação etanólica e efeitos sobre uma linhagem industrial de Saccharomyces cerevisiae
Silva, Lincon Felipe Lima
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One of the main contaminant yeast is Dekkera bruxellensis being known its ability to produce volatile phenolic compounds such as 4-vinylphenol (4-VP) and 4-ethylphenol (4-EP) from hydroxycinnamic acids through the activity of the enzymes cumarate decarboxylase (CD) and vinylphenol reductase (VR), respectively. Hydroxycinnamic acids are present in the sugarcane juice as well as molasses and, thus, 4-EF could be synthesized during Brazilian ethanol fermentation conditions and act as metabolism inhibitors of Saccharomyces cerevisiae. The objective of this work was initially quantify the specific activities of the enzymes CD and VR of three strains of D. bruxellensis isolated from the ethanolic fermentation and two industrial strains of S. cerevisiae (PE-2 and CAT-1). Following the production of 4-EP in fermentations with and without cell recycle utilizing molasses and sugarcane juice as fermentation media by the strains of D. bruxellensis and one industrial strain of S. cerevisiae (PE-2) was evaluated. The effect of p-coumaric acid, 4-VP and 4-EP on the growth of S. cerevisiae PE-2 was also evaluated in semi-synthetic medium. The D. bruxellensis strains showed maximum specific enzymatic activity (U/mg protein) CD of 184.44 up to 215.52 and VR of 101.94 up to 154.26. Although the S. cerevisiae strains also showed CD and VR enzymatic activities, that there was no 4-EP production under fermentation conditions. The fermentative tests without cell recycle showed that the highest values for 4-VP and 4-EP occurred after 24 h during the exponential phase of growth and were stable until 72 h of fermentation in sugarcane juice and molasses. Comparatively the concentrations of 4-EP were higher in the fermentations with cell recycle especially in molasses, with D. bruxellensis CCA077 being the largest producer, 9.47 mg/L, in the first 12-h fermentative cycle already. There was no inhibitory effect of p-coumaric acid, 4-VP and 4-EP at concentrations of 4 to 20 mg/L, 2 to 10 mg/L and 3 to 15 mg/L, respectively, on the maximum specific growth rate of the S. cerevisiae PE-2 strain.