The lignocellulosic by-products, whole stones, and seed husks obtained from processing pitted table olives and oil olives were pretreated under various conditions of steam explosion, with and without previous acid impregnation. The various water-soluble noncarbohydrate compounds generated during steam explosion, such as sugar degradation compounds (furfural and hydroxymethylfurfural), lignin degradation compounds (vanillic acid, syringic acid, vanillin, and syringaldehyde) and the simple phenolic compounds characteristic of olive fruit (tyrosol and hydroxytyrosol), were identified. The amount of hydroxytyrosol solubilized was higher than that of the other compounds, and increased with increasing steaming temperature and time. This suggests its presence as a structural component of the olive stone.Olive stones have a high content of lignocellulosic material and are an important by-product of table olive processing. Pitted table olives make up 70-75% of total table olive production (1). The olive pomace obtained from olive fruit processing contains seed husk and a small amount of seeds, pulp, and peel, which can be separated by common industrial methods.Research related to oil, proteins, sugars, and phenolic compounds of olive seed has been carried out (2-5), but information related to the seed husk is scarce. However, the fiber of olive seed husks has been studied (6), and its polysaccharides have been characterized (7).The lignocellulosic products are currently used as an energy source, and have recently been employed to produce activated carbon (8). Steam explosion treatment (explosive autohydrolysis) has been extensively studied as a promising pretreatment process (9,10) to separate and increase the accessibility of main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin). During steam explosion, the lignocellulosic material is split, and lignin is partly depolymerized (11), giving rise to phenolic compounds which are water-soluble and have inhibitory action against microorganisms (12,13).Olive leaves and fruit contain a considerable amount of phenolic compounds, mainly oleuropein, which, apart from their inhibitory action against microorganisms (14), have an antioxidant effect on the oxidative stability of oils (15). Some of these phenolic compounds are contained in the olive fruit processing by-products.In this study, the simple phenolic compounds obtained from the steam explosion of whole stones and seed husks were characterized and quantified, and the effect of temperature and time during steam explosion on the yield of these phenolic substances was evaluated. EXPERIMENTAL PROCEDURESMaterials. Whole olive stones were obtained from pitted table olives dried in an air stove at 30ºC and rubbed vigorously on a filter paper to remove any loosely adhering pulp tissue. Olive seed husks were supplied by an oil extraction plant (Oleícola el Tejar, Córdoba, Spain). The husks were obtained from olive pomace after separating peel, pulp, and seeds.Steam treatment. The steam explosion treatments ...

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Olive cake was processed by steam-explosion under different steam conditions, followed by fractionation to separate the main components. In the water-soluble fraction, the main compounds were carbohydrates. Glucose represented 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 material. In the ethyl acetate extract, low molecular weight phenols were identified, the most abundant being hydroxytyrosol, which is present in the olive pulp. Hydroxytyrosol is abundant and has great antioxidant activity, reaching 149 mg/100 g of dry olive cake. The procedure used in this study obtained all the hydroxytyrosol residual present in the by-product. The constitutive polymers were quantified in the insoluble fraction, and the sugar composition showed that cellulose was associated with a high proportion of xylans and other polysaccharides rich in arabinose and galactose. This cellulose was nearly amorphous, as it was highly susceptible to hydrolytic enzymes. The extractables in dilute alkali (not true lignins) increased as steaming became more severe; the residual "lignin" in this fraction decreased. Enzymatic 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 residues were efficiently delignified with chlorite treatment, the susceptibility to enzymatic hydrolysis greatly increased.Paper no. J9149 in JAOCS 77, 15-22 (January 2000).Olive cake is a by-product derived from the olive oil extraction industry. It is obtained by pressing the fruit, leaving a residue of seed husks (fragmented olive stones), seed, pulp and peel (olive cake). Olive-mill wastewater and/or vegetation water is also obtained. Olive cake has been utilized as an energy source, fertilizer, and animal feed (1). In spite of its high fiber and protein contents, this by-product has low nutritional value owing to phenolic compounds inhibiting digestive enzymes. During oil extraction, polymers are formed among the phenolic substances themselves and/or protein and cellulose so that they are unavailable for ruminant digestion. Consequently, these polymers constitute an integral part of the cell wall component and show physical and chemical properties very similar to lignin (2). By way of certain pretreatments, it is possible to reduce the degree of lignification of the olive cake, thus enhancing its nutritional value.High-pressure steaming followed by rapid decompression is called steam-explosion. Recently, steam-explosion has been considered an effective pretreament (3) of waste cellulosic materials for further processing, including olive stones (4,5). The resultant material is finely divided; and the main components-cellulose, hemicelluloses, and lignin-are separated...

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