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Project ID: ICA3-CT-2002-10033
Finanziato nell'ambito di: FP5-INCO 2
Paese: Tunisia

Liquid extraction of phenolic compounds/ hydroxytyrosol from OMW: Evaluation of their antioxidant and biological effects

The olive oil market has recently developed, since the “Mediterranean diet” is widely appreciated throughout the world by consumers more attentive to both health and nutritional aspects of food. The increasing popularity of olive oil has been mainly attributed to its high content of oleic acid, which may affect the plasma lipid/lipoprotein profiles and its richness in phenolic compounds acting as natural antioxidants, which may contribute to the prevention of diseases in human. However, during olive oil extraction the addition of water resulted in the release of the major part of olive polyphénols in the liquid phase (vegetation water) due to their amphiphilic character.

High added value antioxidants present in olive oil are found in olive oil processing by-products at very high concentrations. In particular, olive oil mill wastewaters, which become a major environmental problem in the main olive producing countries of the Mediterranean region, could be considered as a source of natural antioxidants.

Our objective was to develop effective procedures to recover potentially high-added-value phenolic compounds contained in OMW. Biological activities of the major compound and extracts were carried out in vivo and in vitro in order to evaluate their antioxidant and potential application as food additives and for stabilisation of refined husk oil.

A process was developed to extract and purify hydroxytyrosol, one of the major compounds occurring in OMW. Batch optimization experiments showed that ethyl acetate is the most efficient solvent for the recovery of phenolic monomers from OMW. The latter was used with an optimal pH equal to 2. Furthermore, the percentage of each monomer and particularly hydroxytyrosol in the extract was maximum for a solvent ratio and a theoretical extraction stage numbers equal to 2 and 3, respectively.

High yield (85.46%) recovery of hydroxytyrosol was achieved from OMW using a three-staged continuous counter-current liquid-liquid extraction unit. 1.225 g of hydroxytyrosol were extracted per liter of OMW. One gram of hydroxytyrosol per liter of OMW was then purified by means of a chromatographic system which could be adapted to a large scale production process.

The effects of OMW origin (time of olive harvest, process of olive oil extraction) and storage method were studied with regard to the recovered phenolic compound concentration, particularly hydroxytyrosol. OMW storage in the darkness, at 25°C in intermittent agitation and aerobic condition for 3 to 5 months led to an increase in the concentration of hydroxytyrosol.

The antiradical and antioxidant activities of the OMW extract as well as pure phenolic compounds identified in this extract were evaluated. Results showed that pure hydroxytyrosol and 3,4-dihydroxyphenyl acetic acid had the highest radical scavenging effect on 1.1 diphenyl -2 picrylhydrazyl (DPPH) radical and the highest antioxidant activities using the ?-carotene linoleate model system .

The effect of addition of individual phenolic compounds and OMW extract to refined olive and husk oils was compared with that of control, BHA and BHT at 50 °C. 3,4-dihydroxyphenyl acetic acid and hydroxytyrosol have the highest protective effect against oil oxidation The results suggested that hydroxytyrosol and OMW extract possess useful antioxidant properties and may be used as alternative in the search for natural replacement of synthetic antioxidant food additives.

Hypocholesterolemic effects of hydroxytyrosol and OMW extract in rats fed a cholesterol-rich diet were tested. Wistar rats, fed a standard laboratory diet or a cholesterol-rich diet for 16 weeks, were used. Serum lipid levels, as well as thiobarbituric acid reactive substances (TBARS) and superoxide dismutase (SOD) and catalase (CAT) activities in liver were examined. Cholesterol-rich diet induced hypercholesterolemia was manifested in the elevation of serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C).

Administration of a low-dose (2.5 mg/kg of body weight) of hydroxytyrosol and high-dose (10 mg/kg of body weight) of OMW extract significantly lowered the serum levels of TC and LDL-C while increasing the serum levels of high density lipoprotein cholesterol (HDL-C). Furthermore, the TBARS contents in liver, heart, kidney and aorta, decreased significantly after oral administration of hydroxytyrosol and OMW extract compared with those of rats fed a cholesterol-rich diet. In addition, OMW phenolics increased CAT and SOD activities in liver. These results suggested that the hypocholesterolemic effect of hydroxytyrosol and OMW extract might be due to their abilities to lower serum TC and LDL-C levels as well as slowing the lipid peroxidation process and enhancing antioxidant enzyme activity.

Informazioni correlate


Sami SAYADI, (Head Laboratory of Bioprocesses)
Tel.: +216-74440452
Fax: +216-74440452