Effect of inoculum concentration and nutritional supplementation on Kluyveromyces marxianus NRRL Y-6860 fermentative performance

Kluyveromyces marxianus strains are excellent ethanol producers and its fermentative potential have been demonstrated in a wide variety of carbohydrate materials, including lignocellulosics. Recently, K. marxianus NRRL Y-6860 was selected in our laboratories due to its ability to produce ethanol from glucose above 40 °C. In this context, the aim of this study was to evaluate the influence of initial inoculum concentration and nutritional supplementation on K. marxianus NRRL Y-6860 ethanol production using semi-synthetic medium at 43 °C. For this purpose, experiments were performed employing 2^5-1 factorial design varying (NH₄)₂SO₄ (1.0 – 3.0 g/L), KH₂PO₄ (0.5 – 1.5 g/L), MgSO₄ (0.1 – 0.5 g/L), yeast extract (3.0 – 7.0 g/L) and inoculum concentration (1.0 – 5.0 g/L). The fermentation was carried out in 125 mL Erlenmeyers flasks containing 50 mL medium (120 g/L of glucose) under 100 rpm agitation. Statistical analysis of the results showed that among the five variables studied only inoculum concentration and yeast extract have significant effects on the ethanol production (p < 0.10 and R² = 0.98). The main effects were (+ 10.15) and (- 6.01), respectively, suggesting that the higher levels of inoculum concentration and lower levels of yeast extract improve the ethanol fermentation. In these conditions, maximum ethanol concentration was around 40 g/L and Y_P/S of 0.47 g/g. Further experiments exploring lower concentrations of salts are still necessary to optimize the fermentative parameters, since in the evaluated range these compounds were not statistically significant.

Supported by FAPESP, CNPq and CAPES (BRAZIL)