D-XYLOSE PRODUCTION FROM ENDOCARP OF OLIVE FRUIT: OPTIMIZATION OF DILUTE SULPHURIC-ACID HYDROLYSIS

摘要

Endocarps in fragments from olive fruits (EF) have a high content of xylans and could be a potentialmaterial for production to D-xylose by hydrolysis with inorganic acids. Hydrolysis of EF by diluted sulphuric acid athigh temperature was researched in this study. Firstly, the effects of two operational conditions, including reactiontemperature (180–220°C) and time (2–8 min), on monosaccharides yields were examined using a 2~2 factorial design.An acid concentration of 0.01 M and a solid/liquid ratio of 1/6 were set. D-xylose was the major sugar in thehydrolysates, with a maximum yield above 0.20 kg kg~(–1)EF that was achieved at 201°C reaction temperature for 5.2min. Under those conditions the low content of L-arabinose, D-galactose, and D-glucose (< 0.01 kg monosaccharidekg~(–1)EF), and of the fermentation inhibitors (< 0.001 kg HMF kg~(–1)EF; < 0.033 kg acetic acid kg~(–1)EF) provided aninteresting subtract for its biochemical conversion to xylitol or ethanol. Finally, a new factorial design was developed,with the optimal condition derived from the first experimental series, to study the effect of acid concentration (0.01–0.03 M) and solids loading (50–150 g) on sugars production. Although the maximum D-xylose yield decreased withthe increase of solid/liquid ratio, the conditions that release more pentoses at high solids loading were determined.Thus, it was possible to obtain direct hydrolysates with D-xylose concentrations close to 85 g dm–3. This researchdemonstrates that the response surface methodology (RSM) can be employed for optimising the D-xylose productionby acid hydrolysis of olive stone, and that the raw material is a rich source of pentoses.