Hydrothermal Treatments of Cistus ladanifer Industrial Residues Obtained from Essential Oil Distilleries

Purpose The aim of this study was to optimize hydrothermal treatments (autohydrolysis) for selective hydrolysis of hemicelluloses in the residues obtained from the industrial steam distillation of Cistus ladanifer (rock-rose) for essential oil extraction (CLR). The effect of the autohydrolysis in the removal of extractives of these residues was also evaluated.MethodsThe raw material was treated with water in a 6:1 liquid-to-solid ratio (w/w) and the effect of temperature (130-230 degrees C) on the composition of liquid and solid phases were evaluated and interpreted using the severity factor (log R-0). Results The highest recovery of oligosaccharides (24.7 g/L), corresponding to a yield of 28.4 g/100g of CLR was obtained at moderate conditions, log R-0 of 3.12. Together with hemicelluloses, polar extracts were also largely solubilized during the hydrothermal process yielding hydrolysates with a relevant concentration of phenolics. The highest glucan content (35.6g/100g of CLR) of the solid residue was obtained at more severe conditions, log R-0 of 4.0 (220 degrees C). There was no apparent lignin solubilisation in any of the conditions, which is an advantage of this hydrolytic pretreatment. Conclusions Cistus ladanifer residues demonstrated to have potential to be used in the biorefinery framework with a full upgrade of all biomass fractions.