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Filtration of veiled virgin olive oil samples indicated a loss in stability that was assigned to a loss in total polyphenol content. Oil samples, after filtration, had quite similar peroxide values and absorbance in the UV region to the respective veiled ones. Nine months storage of veiled and filtered oils at ambient temperature, in the dark, revealed that gradual loss in stability, expressed as OSI values, was greater in the latter. This finding was reflected by the greater increase in peroxide values and also faster decrease in total polar phenol content in filtered samples. The RP-HPLC analysis of the phenolic fractions, at various stages of storage, indicated interesting differences in the evolution of individual phenols between the two types of samples. It is suggested that, not only the higher content, but also the forms of individual phenols liberated in veiled oils, due to hydrolytic processes, may be responsible for the unexpected high oxidative stability of this promising commercial category of virgin olive oil.

An olive oil – lemon juice Greek salad dressing was developed employing xanthan gum as stabilizer and gum arabic or propylene glycol alginate as emulsifier in various combinations. In general, samples containing xanthan gum arabic were more stable against oil droplet coalescence and less stable against creaming. The use of propylene glycol alginate in the place of gum arabic, on the other hand, resulted in emulsions of higher creaming stability. Application of steady shear rheology and determination of rheological parameter values from the shearing stress-rate of shear curves, indicated that the rheological properties of the dressings were decreased with storage. Dressing texture assessment preference tests indicated that potential consumers of the product may opt for a medium viscosity product and this has to be taken into consideration when designing polysaccharide – stabilized dressings exhibiting a decrease in their textural characteristics with storage time.

Intramolecular hydrogen bonds in crystals and in apolar media are well documented, however, the degree to which they persist in aqueous solution is controversial. We report here variable temperature gradient 1 H, 1 H– 13 C Gradient Enhanced Heteronuclear Single Quantum Correlation (GE-HSQC) and Gradient Enhanced Heteronuclear Multiple Bond Coherence (GE-HMBC) NMR studies of the flavonols quercetin and kaempferol and the flavone luteolin, in organic solvents and in mixtures of organic–aqueous solutions. It is demonstrated that the strong intramolecular hydrogen bond of the –CO(4) and –OH(5) moieties persists over a wide range of aqueous mixtures and, thus, provide a rare example of non-charged intramolecular hydrogen bonds, which is not overwhelmed by solvation with protic solvents, in particular in aqueous solution.

Hexane extracts obtained by percolation from the leaves of nine Mediterranean plants ( Daphne oleoides , Myrtus communis , Pelargonium zonale , Phillyrea latifolia , Pistacia terebinthus , Quercus pubescens , Rhamnus lucioides , Sideritis syriaca , Smilax aspera ) and from five leaf spices ( Rosmarinum officinalis , Coridothymus capitatus , Laurus nobilis , Salvia fruticosa , Salvia pomifera ) were examined for the presence of tocopherols by thin layer chromatography, gas chromatography, high performance liquid chromatography and combined gas chromatography–mass spectrometry. With the exception of Sideritis syriaca , in all the plants and spices examined α-tocopherol was found to be present. The β - and γ -homologues were detected only in the extracts of Pelargonium zonale and Smilax aspera . Quantitative analysis by HPLC gave values ranging from 250 to 1325 ppm total tocopherols (on a dry leaf basis). These values are higher than those reported for oil seeds (sunflower seed, cottonseed, rapeseed, sesame seed) or other oil sources (peanut, soybean, maize).

The effect of 100, 500 and 1000 ppm of α-tocopherol on the oxidative stability of purified olive oil kept in the dark at 40 °C was studied. Purified olive oil was prepared by liquid column chromatography and was practically devoid of minor constituents with possible pro-oxidant or antioxidant activity. α-Tocopherol acted as antioxidant at all levels of addition, although the antioxidant effect was greater at 100 ppm than at higher concentrations. In the initial stage of autoxidation a slightly pro-oxidant effect was observed. In the presence of strong antioxidants naturally occurring in olive oil, such as ortho-diphenols, α-tocopherol did not show any significant additional antioxidant effect during the period of low peroxide accumulation.

The stability of 24 samples of Greek virgin olive oil was examined in relation to total polyphenol content, and individual phenols were determined by reversed-phase HPLC. Tyrosol, the major olive-oil phenol, is not correlated with the shelf-life of the oil. Total polyphenol content and hydroxytyrosol-to-tyrosol ratio have a significant linear correlation with the resistance of the oil to autoxidation.