Steam-explosion of olive stones: hemicellulose solubilization and enhancement of enzymatic hydrolysis of cellulose

Olive stones (whole stones and seed husks in fragments) were processed by s team-explosion under different experimental conditions of temperature and t ime, 200-236 degreesC for 2-4 min, with or without previous acid impregnati on with 0.1% H2SO4 (w/w). This paper examines the solubilization of hemicel luloses and their molecular weight distribution. The subsequent enzymatic h ydrolysis of the solid residue, using a preparation of cellulase, was also studied. The maximum yield of the pentosan recovered in the water solution was 63%, pentose in the starting material for seed husk treated at 200 degr eesC for 2 min (log R-0 3.24) prior to acid-impregnation, or at 215 degrees C for 2 min (log R-0 3.69) without acid, compared to 39% of the potential y ield for whole stones pre-impregnated with acid under more severe condition s (at log R-0 = 4.07). This indicates that the autohydrolysis of hemicellul ose in seed husks when compared to whole stones is enhanced. The molecular weight distribution of profile sugars showed that the depolymerization of h emicelluloses is a function of the severity of the treatment. Steam-explosi on improved the accessibility of the cellulose and increased the enzymatic hydrolysis yield after steam-explosion with respect to material without ste am explosion (ball-milled material), although little increase in the extent of saccharification occurred when the alkali-soluble lignin was removed. O nly when the substrate was post-treated with Na-chlorite was the enzymatic hydrolysis improved, the water-insoluble residue being almost completely hy drolyzed in 8 h of incubation. (C) 2001 Elsevier Science Ltd. All rights re served.