Fermentation of acid hydrolysates from olive-tree pruning debris by Pachysolen tannophilus

The influence of the type and concentration of acid in the hydrolysis process and its effect on the subsequent fermentation by Pachysolen tannophilus (ATCC 32691) to produce ethanol and xylitol was studied. The hydrolysis experiments were performed using hydrochloric, sulphuric and trifluoroacetic acids in concentrations ranging from 0.1 to 1.0 N, a temperature of 90 degrees C, and a time of 240 min. The fermentation experiments were conducted on a laboratory scale in a batch-culture reactor at pH 4.5 and 30 degrees C. The hydrolysis with the highest acid concentration produced the complete solubilization of hemicellulose to monosaccharides. The highest values for the specific rate of ethanol production were registered in cultures hydrolyzed with trifluoroacetic acid, and values were found to decrease as the acid concentration increased. The highest values of overall ethanol yields (Y(E/s)(G) = 0.37 kg kg(-1)) were also found in the fermentation of the hydrolysates of trifluoroacetic acid.