Phenolic and orthodiphenolic compounds together with carotenoids, tocopherols, pigments, and fatty acids were tested for their antioxidant effect in 79 samples of virgin olive oils cv. Picual and Hojiblanca. A linear regression based on the oleic/linoleic ratio and the contents of phenols and tocopherols showed a good correlation (adjusted-R(2) = 0.91) with the stability measured by Rancimat, later verified with an external text set (adjusted-R(2) = 0.95). A tentative study on the percentage contribution of each chemical variable to stability is discussed. The contribution of phenolic and orthodiphenolic compounds was around 51%, the composition of fatty acids 24%, and in less percentage alpha-tocopherol, carotenoids, and chlorophylls. No effect, or very little, was shown by beta- and gamma-tocopherols.
A thermoxidation process has been applied to extra-virgin olive oil to
develop new knowledge on
the evolution of the volatile compounds responsible for virgin olive
oil flavor during oxidative
deterioration. The initial volatiles (a total of 60), many of them
responsible for the pleasant sensory
characteristics of the oil and produced mainly through biochemical
pathways, disappeared in the
first hours, and the formation of off-flavors, produced through
oxidative pathways, gradually
increased. The main volatile compounds possibly responsible for
off-flavors (51) were identified,
and their evolution during the oxidative process was studied. The
fatty acids content was determined
during the process. Unsaturated fatty acids were found to be the
main precursors of the volatile
compounds found in oxidized samples. The early measurement of
nonanal (which was not detected
at all, or only at trace levels, in extra-virgin olive oil samples)
could be an appropriate method to
detect the beginning of the oxidation. The ratio hexanal/nonanal
was used to differentiate between
oxidized and good-quality virgin olive oil samples. Sensory
evaluation of the samples and peroxide
value agreed on the evolution of the oxidation.
Keywords: Oxidation; volatiles; flavor; off-flavor; virgin olive
oil
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