Phenolic compounds in olive oil: antioxidant, health and organoleptic activities according to their chemical structure.

Hydrophilic phenols are the most abundant natural antioxidants of virgin olive oil (VOO), in which, however, tocopherols and carotenes are also present. The prevalent classes of hydrophilic phenols found in VOO are phenolic alcohols and acids, flavonoids, lignans and secoiridoids. Among these substances the last two classes include the most concentrate phenols of VOO. Secoiridoids, like aglycone derivatives of oleuropein, demethyloleuropein and ligstroside, are present in olive fruit as most abundant VOO phenolic antioxidants. Several important biological properties (antioxidant, anti-inflammatory, chemopreventive and anti-cancer) and the characteristic pungent and bitter tasty properties have been attributed to VOO phenols. Relationships between polyphenols activities and their chemical structures are discussed in this paper.

Cancer chemoprevention by hydroxytyrosol isolated from virgin olive oil through G1 cell cycle arrest and apoptosis.

Recent epidemiological evidence and animal studies suggest a relationship between the intake of olive oil and a reduced risk of several malignancies. The present study assesses the effect of hydroxytyrosol, a major antioxidant compound of virgin olive oil, on proliferation, apoptosis and cell cycle of tumour cells. Hydroxytyrosol inhibited proliferation of both human promyelocytic leukaemia cells HL60 and colon adenocarcinoma cells HT29 and HT29 clone 19A. The con-centrations of hydroxytyrosol which inhibited 50% of cell proliferation were approximately 50 and approximately 750 micromol/l for HL60 and both HT29 and HT29 clone 19A cells, respectively. At concentrations ranging from 50 to 100 micromol/l, hydroxytyrosol induced an appreciable apoptosis in HL60 cells after 24 h of incubation as evidenced by flow cytometry, fluorescence microscopy and internucleosomal DNA fragmentation. Interestingly, no effect on apoptosis was observed after similar treatment of freshly isolated human lymphocytes and polymorphonuclear cells. The DNA cell cycle analysis, quantified by flow cytometry, showed that the treatment of HL60 cells with hydroxytyrosol 50-100 micromol/l arrested the cells in the G0/G1 phase with a concomitant decrease in the cell percentage in the S and G2/M phases. These results support the hypothesis that hydroxytyrosol may exert a protective activity against cancer by arresting the cell cycle and inducing apoptosis in tumour cells, and suggest that hydroxytyrosol, an important component of virgin olive oil, may be responsible for its anticancer activity.

Effect of enzyme treatment during mechanical extraction of olive oil on phenolic compounds and polysaccharides.

The effect of the use of cell-wall-degrading-enzyme preparations during the mechanical extraction process of virgin olive oil on the phenolic compounds and polysaccharides was investigated. The use of the enzyme preparations increased the concentration of phenolic compounds in the paste, oil, and byproducts. Especially, the contents of secoiridiod derivatives such as the dialdehydic form of elenolic acid linked to 3,4-dihydroxyphenylethanol (3,4-DHPEA-EDA) and an isomer of oleuropein aglycon (3,4-DHPEA-EA), which have high antioxidant activities, increased significantly in the olive oil. Furthermore, the use of an N(2) flush during processing strongly increased the phenolic concentration. Analyses of the pectic polymers present in the paste showed that the use of pectinolytic enzyme preparations increased the yield of the buffer soluble pectins and the proportion of molecules with a lower molecular mass. Also, the content of uronic acids in the buffer soluble extract increased considerably due to the use of the enzyme preparations. Analysis of the polymeric carbohydrates in the vegetation waters showed the presence of mainly pectic polymers. The addition of commercial enzyme preparations increased the uronic acid content of the polysaccharides in the vegetation water substantially compared to the blank. This study showed that the addition of cell-wall-degrading enzymes did improve the olive oil quality; however, mechanisms remained unclear.

Inhibition of platelet aggregation and eicosanoid production by phenolic components of olive oil.

This study was designed to investigate the in vitro effects of phenolic compounds extracted from olive oil and from olive derived fractions. More specifically, we investigated the effects on platelets of 2-(3,4-di-hydroxyphenyl)-ethanol (DHPE), a phenol component of extra-virgin olive oil with potent antioxidant properties. The following variables were studied: aggregation of platelet rich plasma (PRP) induced by ADP or collagen, and thromboxane B2 production by collagen or thrombin-stimulated PRP. In addition, thromboxane B2 and 12-hydroxyeicosatetraenoic acid (12-HETE) produced during blood clotting were measured in serum. Preincubation of PRP with DHPE for at least 10 min resulted in maximal inhibition of the various measured variables. The IC50s (concentration resulting in 50% inhibition) of DHPE for ADP or collagen-induced PRP aggregations were 23 and 67 microM, respectively. At 400 microM DHPE, a concentration which completely inhibited collagen-induced PRP aggregation, TxB2 production by collagen- or thrombin-stimulated PRP was inhibited by over 80 percent. At the same DHPE concentration, the accumulation of TxB2 and 12-HETE in serum was reduced by over 90 and 50 percent, respectively. We also tested the effects of PRP aggregation of oleuropein, another typical olive oil phenol, and of selected flavnoids (luteolin, apigenin, quercetin) and found them to be much less active. On the other hand a partially characterized phenol-enriched extract obtained from aqueous waste from olive oil showed rather potent activities. Our results are the first evidence that components of the phenolic fraction of olive oil can inhibit platelet function and eicosanoid formation in vitro, and that other, partially characterized, olive derivatives share these biological activities.