Evaluation of stress tolerance and fermentative behavior of indigenous Saccharomyces cerevisiae

Abstract

Sixty six indigenous Saccharomyces cerevisiae strains were evaluated in stressful conditions (temperature, osmolarity, sulphite and ethanol tolerance) and also ability to flocculate. Eighteen strains showed tolerant characteristics to these stressful conditions, growing at 42 °C, in 0.04% sulphite, 1 mol L(-1) NaCl and 12% ethanol. No flocculent characteristics were observed. These strains were evaluated according to their fermentative performance in sugar cane juice. The conversion factors of substrates into ethanol (Y(p/s)), glycerol (Y(g/s)) and acetic acid (Y(ac/s)), were calculated. The highest values of Y(p/s) in sugar cane juice fermentation were obtained by four strains, one isolated from fruit (0.46) and the others from sugar cane (0.45, 0.44 and 0.43). These values were higher than the value obtained using traditional yeast (0.38) currently employed in the Brazilian bioethanol industry. The parameters Y(g/s) and Y(ac/s) were low for all strains. The UFLA FW221 presented the higher values for parameter related to bioethanol production. Thus, it was tested in co-culture with Lactobacillus fermentum. Besides this, a 20-L vessel for five consecutive batches of fermentation was performed. This strain was genetically stable and remained viable during all batches, producing high amounts of ethanol. The UFLA FW221 isolated from fruit was suitable to produce bioethanol in sugar cane juice. Therefore, the study of the biodiversity of yeasts from different environmental can reveal strains with desired characteristics to industrial applications.

Keywords: Saccharomyces cerevisiae; UFLA FW221; alcoholic fermentation; biofuel; fermentation kinetics.

Figure 1

Dendrogram obtained by Ward’s hierarchical clustering method performed for different growth conditions (temperature, osmolarity, sulfite and ethanol tolerance and flocculation capacity). G1 = most resistant strains (Growth at 42 °C, in 1 M NaCl, 0.04% (w/v) sulfite and tolerated 12% ethanol. They were not flocculent) and G2 = most sensitive strains.

Figure 2

Principal component analysis (PCA) of the kinetic parameters of 19 S. cerevisiae strains in sugar cane juice.

Figure 3

Principal component analysis (PCA) of the kinetic parameters of four selected S. cerevisiae strains in sugar cane juice.

Figure 4

Results obtained in the fermentation employing S. cerevisae UFLA FW221 in co-culture with L. fermentum. a. Rates of CO₂ (dCO₂/dt) production; b. Carbohydrates and ethanol yields; c. Growth of S. cerevisiae UFLA FW221and L. fermentum strains evaluated by plating in YPD and MRS medium, respectively, in pure and co-culture during sugar cane juice fermentation.

Figure 5

Pulsed Field Gel Electrophoresis (PFGE) of strains isolated in the five batches. Numbers represents the batches.

Figure 6

Viable S. cerevisiae cells stained with the Live/Death Yeast Viability kit and viewed by fluorescent microscopy after five batches.

Figure 7

Biomass production by UFLA FW221 during five batches (20 L) in sugar cane juice fermentation. T0 = initial time of batch, TF = final time of batch.