Fermentation of olive tree pruning acid-hydrolysates by Pachysolen tannophilus

The influence of hydrolysis conditions on the fermentation of hydrolysates obtained from olive tree pruning (a renewable, low cost, largely available agricultural residue) is analyzed in this work. Hydrolysis was performed using sulfuric acid at atmospheric pressure (90 °C) in a concentration range of 0.5–4N for 240 min. The fermentation of hydrolysates was carried out by Pachysolen tannophilus in a discontinuous tank bioreactor at 30 °C and pH 3.5. The main fermentation parameters determined in this study include maximum specific growth rate, biomass productivity, specific substrate consumption rate, specific ethanol production rate, and ethanol and xylitol yields. The results show that ethanol yields are much higher than xylitol yields under all the conditions tested. The maximum ethanol yield (0.38 g/g) is reached with the hydrolysate obtained with 0.75N sulfuric acid. Under these conditions the conversion of the hemicellulose fraction is 92%.