Loss of stability of “veiled” (cloudy) virgin olive oils in storage

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.