Anais do Congresso Paranaense de Microbiologia
Anais do III Congresso Paranaense de Microbiologia

Yeast propagations for the production of fermented beverages are commonly processed as baker’s yeast. Although the system is fully aerated, a respiro-fermentative metabolism can be verified as a consequence of the Crabtree effect, leading to low biomass concentrations. In this research, we evaluated the capacity of brewer’s yeast strains to grow on oxidative substrates such as ethanol and glycerol. The ale (TB07) and lager (TB81) yeast strains cultured were donated by Levteck Tecnologia Viva (Florianópolis, Brazil). Growth was conducted on aerated Erlenmeyers containing 350 mL of medium. All media contained in grams per liter of deionized water: Yeast Extract, 1; MgSO4.7H2O, 0,4; (NH4)2HPO4, 1.3; CaCl2, 0.6; Fe2SO4, 0.05; KH2PO4, 1.5; NaCl, 0.5. The proportions of ethanol (1 – 5 g.L-1) and glycerol (6.5 – 20 g.L-1) varied based on the assay conducted. A single colony of the strain was inoculated in Erlenmeyers and grew for 48 hours at room temperature (23°C). Ethanol evaporation was evaluated by repeating the analyses without inoculation. Biomass concentration was determined by linear correlations (R2 = 0.994 for TB81; R² = 0.999 for TB07) with optical density of cell suspensions (570 nm). Ethanol concentration was quantified by Anton Paar's Alcohol Meter and glycerol by triglycerides assay. Final biomass concentrations and yield coefficients on media containing 1 – 5 g.L-1 of ethanol were 0.12 – 0.18 g.L-1 and 0.24 – 0.11 (g biomass)ꞏ(g ethanol)-1 for TB07 meanwhile 0.55 – 0.30 g.L-1 and 0.44 – 0.11 (g biomass)ꞏ(g ethanol)-1 for TB81, respectively. For glycerol media varying between 6.5 – 20 g.L-1, the values reached 0.08 – 0.11 g.L-1 and 0.07 – 0.02 (g biomass)ꞏ(g glycerol)-1 for TB07 while 0.28 – 0.20 g.L-1 and 0.24 – 0.12 (g biomass)ꞏ(g glycerol)-1 for TB81. Around 16% from 1 g.L-1 and 33% from 5 g.L-1 of ethanol were lost through evaporation. The results indicate a better capacity of growing on ethanol than glycerol for both strains. Moreover, ethanol loss through evaporation was greater when present in higher concentrations. This is the first time that the growth of brewer’s yeasts is evaluated on oxidative substrates, indicating their potential application in new propagation processes.