Olives and olive oil contain phenolic compounds (Tsimidou et al., 1992; Tsimidou, 1998) that, in vitro, have been shown to exert potent biological activities including but not limited to antioxidant actions (Visioli et al., 1998). Visioli et al. (1999) reported that OMWW extracts contain potent antioxidants. Among these polyphenols, hydroxytyrosol has been revealed to be the most interesting because of its remarkable pharmacological and antioxidant properties. Hydroxytyrosol originates in all likelihood from the hydrolysis of oleuropein by means of an esterase during the mill process. Chikamatsu et al. (1996) found that hydroxytyrosol inhibits the formation of melanin and lipid peroxides and they patented its use in topical and bath preparations. Because hydroxytyrosol is commercially unavailable, chro-matographic methods of purification from OMWW, virgin olive oil, olive leaves and synthetic procedures could allow a natural and non-toxic anti-oxidant to be obtained. Recovery of hydroxytyrosol could be a useful process for recycling OMWW, thus resolving its disposal problem, albeit partially. Capasso et al. (1999) synthesized hydroxytyrosol by reducing 3,4-dihydroxyphenylacetic acid with LiAlH4 in tetrahydrofuran under refluxing for 2 h. The yield of the reaction was 82.8%. The spectroscopic and highpower liquid chromatography (HPLC) data of the synthesized compound proved to coincide fully with those of a pure sample obtained by chroma-tographic recovery from OMWW (yield = 91 mg L-1). This synthetic method appears to be the most convenient compared with those reported in the literature and is more convenient than chromatographic recovery. It consists of only one step, the reaction is completed in 2 h and it gives a yield of 82.8% starting from 3,4-dihydroxyphenylacetic acid, which is a commercially available product. It is also more convenient than the chro-matographic purification methods from OMWW because they produce hydroxytyrosol in small amounts and are more expensive than the synthesis method.

The ability of OMWW extracts to scavenge superoxide, already reported for hydroxytyrosol and oleuropein (Visioli et al., 1998) is suggestive of a potential use of OMWW extracts in environments in which Fenton and Haber-Weiss reactions take place and in which the concomitant production of superoxide and nitric oxide would yield the powerful oxidant peroxi-nitrite. It is noteworthy that the established antioxidants vitamin E and BHT do not scavenge superoxide, and thus OMWW extracts may add stability to products exposed to high superoxide levels. The protection from hypochlorous acid-induced damage of catalase is of biological significance due to the well-known protein-damaging activity of HOCl, which is produced in biological systems at the site of inflammation by activated neu-trophilis through the enzyme myeloperoxidase (Aruoma and Halliwell, 1987). Also, because foods often come into contact with chlorine-based bleaches, employed as disinfectants in food plants, the use of HOCl scavengers may provide additional protection against reactive chlorine species. Finally, the potent inhibition of calcium ionophore-stimulated production of LTB4 and its metabolites by human neutrophilis suggests that OMWW extracts exert biological effects beyond their antioxidant capacities. The activity of several enzymes, including those involved in the production of eicosanoids, for example phospholipases and oxygenases, is modulated by the intracellular peroxide tone. Thus, by scavenging reactive oxygen species, OMWW extracts could lower the activity of such enzymes and, in turn, decrease the production of pro-inflammatory factors. Additional studies are needed to verify if such anti-inflammatory effects could also take place in vivo and to establish the exact enzymatic target of the bioactive compounds.

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