**New Olive-Pomace Oil Improved by Hydrothermal Pre-Treatments**

G. Rodríguez-Gutiérrez, A. Lama-Muñoz, M.V. Ruiz-Méndez,

F. Rubio-Senent and J. Fernández-Bolaños *Departamento de Biotecnología de los Alimentos,* 

*Instituto de la Grasa (CSIC), Avda, Seville,* 

*Instituto al Campus de Excelencia Internacional Agroalimentario, ceiA3 Spain*

#### **1. Introduction**

The health properties of virgin olive oil (VOO) are well known in the Mediterranean Diet, in which VOO is the main source of fat (Boskou, 2000). The Mediterranean area provides 97% of the total olive production of the world and represents a major industry in the region (Aragon & Palancar, 2001). The fatty acid composition is not the only healthy component of olive oil; in addition, minor components have high biological activities (Pérez-Jiménez et al., 2007). From the olive oil by-product, the olive-pomace oil (OPO) is obtained. Recent studies have demonstrated the positive benefits of OPO on health, and these effects are due mainly to the presence of minor components (Ruiz-Gutiérrez et al., 2009). The new olive oil extraction processes in the olive mills make the extraction of OPO and the general utilisation of wastes more difficult. New thermal systems are proposed to pre-treat the olive oil wastes to facilitate their utilisation and OPO extraction.

#### **1.1 Olive oil extraction systems**

The manufacturing process of olive oil has undergone evolutionary changes. The traditional discontinuous pressing process was initially replaced by continuous centrifugation, using a three-phase system and later a two-phase system. Depending on the different olive oil production method, there are different kinds of wastes. The classic production of olive oil generates three phases and two wastes: olive oil (20 %), solid waste (30 %) and aqueous liquor (50 %). The solid waste (olive cake or "orujo") is a combination of olive pulp and stones. The aqueous liquor comes from the vegetation water and the soft tissues of the olive fruits, with water added during processing (so-called "alpechin" or "olive-mill waste water"). The presence of large amounts of organic substances (oil, polyphenols, protein, polysaccharides, etc.) and mineral salts represents a significant problem for the treatment of wastewater (Borja et al., 1997).

The use of a modern two-phase processing technique to which no water is added generates oil and a new by-product that is a combination of liquid and solid waste, called "alperujo", "alpeorujo" or "two-phase olive mill waste". This by-product is a high-humidity residue

New Olive-Pomace Oil Improved by Hydrothermal Pre-Treatments 251

addition to others (Rodríguez et al., 2008). The pitted alperujo is frequently centrifuged in the OPO extractor because the new decanter technology allows treating low-fat material for oil extraction, through which crude olive-pomace oil is obtained. After this mechanical extraction, a partially defatted and pitted alperujo is obtained, with a humidity close to 50%. This material is dried to no more than 10% humidity for both solvent extraction and combustion. Drying consumes much energy, therefore attempts are continuously to reduce energy costs and to avoid the appearance of undesirable compounds in pomace-olive oil formed by the high temperatures (up to 500 ºC) such as polycyclic aromatic hydrocarbons (PAHs) (León -Camacho et al., 2003) or oxidised compounds (Gomes and Caponio, 1997).

Fig. 1. General scheme of industrial olive oil and olive-pomace oil extraction and by-product

processing.

with a thick sludge consistency that contains 80 % of the olive fruit, including skin, seed, pulp and pieces of stones, which is later separated and usually used as solid fuel (Vlyssides et al., 2004). In Spain, over 90 % of olive oil mills use this system, which means that the annual production of this by-product is approximately 2,5-6 million tons, depending on the season (Aragon & Palancar, 2001).
