Ethanol and xylitol production by fermentation of acid hydrolysate from olive pruning with Candida tropicalis NBRC 0618

• Olive tree pruning biomass can be a potential source of carbohydrates and bioproducts.
• Pretreatment, acid hydrolysis, concentration and conditioning process were carried out.
• The influence of acid concentration over the fermentation process has been studied.
• A sequential production of ethanol and xylitol has been detected.

Olive tree pruning biomass has been pretreated with pressurized steam, hydrolysed with hydrochloric acid, conditioned and afterwards fermented using the non-traditional yeast Candida tropicalis NBRC 0618. The main aim of this study was to analyse the influence of acid concentration on the hydrolysis process and its effect on the subsequent fermentation to produce ethanol and xylitol. From the results, it could be deduced that both total sugars and d-glucose recovery were enhanced by increasing the acid concentration tested; almost the whole hemicellulose fraction was hydrolysed when 3.77% was used. It has been observed a sequential production first of ethanol, from d-glucose, and then xylitol from d-xylose. The overall ethanol and xylitol yields ranged from 0.27 to 0.38 kg kg−1, and 0.12 to 0.23 kg kg−1 respectively, reaching the highest values in the fermentation of the hydrolysates obtained with hydrochloric acid 2.61% and 1.11%, respectively.