Steam‐explosion pretreatment of olive cake

Abstract

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...

Use of Whole Cells ofPseudomonas aeruginosafor Synthesis of the Antioxidant Hydroxytyrosol via Conversion of Tyrosol

“…Tyrosol, occurring naturally in olive mill wastewater (24), would be an excellent starting material for microbial conversion to hydroxytyrosol. Tyrosol can also be obtained from olive cake (18) and olive stones (19), in both cases by means of steam treatment.…”

Processing, Valorization and Application of Bio-Waste Derived Compounds from Potato, Tomato, Olive and Cereals: A Review

“…Cara, et al [360] applied steam explosion as a preparatory process for the use of olive residues, mainly olive wood as substrate for enzymatic hydrolysis. Furthermore, it was described that olive pomace treated with steam explosion is a good source of fermentable sugars [367]. Likewise, various phenolic compounds (e.g, vanillic acid, tyrosol, hydroxytyrosol) can be separated from olive stones and seed husks by steam explosion [368].…”

“…A prior treatment with chlorite improves the enzymatic hydrolysis [410]. Dufresne, et al [367] used lignocellulosic flour of ground olive stones for the production of poly-(hydroxybutyrate-co-valerate, PHBV)-based composites and reported a significant reinforcing and a stabilization effect. Another study described the incorporation of olive husk flour into a polypropylene matrix [411].…”

Selected Process Alternatives for Biomass Refining: A Review

“…Part of the phenolics present in liquors from hydrothermal processing of LCM comes from extractives and from the partial depolymerization of lignin and breaking of ligninhemicellulose linkages [66]. The depolymerized lignin fraction include p-substituted phenols (with zero, one or two methoxy groups), aldehydes, acetophenones and carboxylic acids.…”