Phenolic fraction of virgin olive oil: an overview on identified compounds and analytical methods fo their determination

Among edible oils, virgin olive oil (VOO) has nutritional, technological and sensory characteristics that make it a unique and basic ingredient of the Mediterranean diet. These properties of VOO are attributed not only to the fatty acid composition (high level of oleic acid), which is not significantly different from refined olive oil (ROO), but especially to the high content of phenolic compounds, which are reduced by refining (bleaching and deodorization phases). Phenolic compounds, acting as natural antioxidants, increase the resistance of the oil to storage and heating. Moreover, phenols are the main contributors to the typical tastes of VOO (bitter and pungent attributes), and may also contribute to the prevention of several human diseases. Polar phenolic compounds belong to different chemical classes: phenolic acids, phenyl ethyl alcohols, flavonoids, lignans and secoiridoids. Approximately 50 compounds present in the phenolic fraction have been separated and identified to date, although researchers have not reached a consensus for the correct identification/denomination for many of these compounds. Due to variety of analytical approaches carried out on the complex phenolic pattern of VOO by high performance techniques, some disagreements have been emphasized. The aim of this review paper is to summarize and critically analyze the available information about phenolic compounds in VOO.