Xylitol production from pretreated olive stone

Olive stone is one of the main lignocellulosic residues derived from olive oil production process. It is currently used for electricity or heat production following a combustion process. Nevertheless, other uses are being considered, especially in conjunction with other olive oil-derived residues such as olive tree biomass or olive pomace, and in particular under the biorefinery concept.

In this work, the possibilities of using olive stone as raw material for xyilitol production is assessed. The procedure included a water extraction at 130ºC for 90 minutes followed by another extraction with dilute sulfuric acid. This results in a solution containing more than 60 g/l of xylose as the main sugar. This liquor contained also up to 16 g/l acetic acid. An experimental study with synthetic sugars in this concentration range was performed with the xylitol producing yeast Candida bodiini. Results showed that this range of sugars is appropriate for xylitol production whereas the acetic acid concentration rendered the liquor not fermentable. As a consequence, different detoxification procedures were assayed. Best results were obtained by using Saccharomyces cerevisiae to consume glucose, furfural and acetic acid. Further process steps include centrifugation, pH adjustment and inoculation of Candida bodinii, a microorgsnism described as capable of producing xylitol. Depending on the starting liquor and the operational conditions, xylitol productions as high as 38 g/l were obtained after 90 h fermentation time.