Steam-explosion pretreatment of olive cake

Olive cake was processed by steam-explosion under different steam condition s, followed by fractionation to separate the main components. In the water- soluble fraction, the main compounds were carbohydrates. Glucose represente d a significant-part of the total monosaccharide content, especially under conditions of mild severity, followed by arabinose, but the solubilization of sugars occurred predominantly in the : oligomeric fraction. Mannitol was also found in significant amounts (1.5%), similar to that in the initial m aterial. In the ethyl acetate extract, low molecular weight phenols were id entified,:the most abundant being hydroxytyrosol, which is present in the o live pulp. Hydroxytyrosol is abundant and has great antioxidant activity, r eaching 149 mg/100 g of dry olive cake. The-procedure used in this study ob tained all the hydroxytyrosol residual present in the by-product. The const itutive polymers were quantified in the insoluble fraction, and the sugar c omposition showed that cellulose was associated with a high proportion of x ylans and other polysaccharides rich in arabinose and galactose. This cellu lose was nearly amorphous, as it was highly susceptible to hydrolytic enzym es. The extractables in dilute alkali (not true lignins) increased as steam ing became more severe; the residual "lignin" in this fraction decreased. E nzymatic hydrolysis of the insoluble fraction using a cellulolytic complex was also studied. The slight increase in the extent of saccharification was not proportional to the high alkaline delignification. However, when the r esidues were efficiently delignified with chlorite treatment, the susceptib ility to enzymatic hydrolysis greatly increased.