Advisor(s)
Abstract(s)
Physicochemical parameters, total phenols contents
(TPC), and oxidative stabilities at 120–160 C were
evaluated for two monovarietal (Arbequina and Cobrançosa
cultivars, cvs.) and one blend extra-virgin olive oil, confirming
the label quality grade and allowing grouping them according
to the different TPC (TPC = 88 7, 112 6 and
144 4 mg CAE/kg, for cv. Arbequina, blend and cv.
Cobrançosa oils, respectively). The lipid oxidation rate
increased with the decrease of the TPC, being Cobrançosa oils
(higher TPC) more thermally stable. Kinetic-thermodynamic
parameters were determined using the activated complex/transition-
state theory and the values did not significantly differ
for Cobrançosa and blend oils, which had the highest TPC,
suggesting a hypothetically threshold saturation of the beneficial
effect. Cobrançosa oils had a significant more negative
temperature coefficient, higher temperature acceleration factor,
greater activation energy and frequency factor, higher positive
enthalpy of activation, lower negative entropy of
activation, and greater positive Gibbs free energy of activation,
probably due to the higher TPC. The results confirmed
that lipid oxidation was a nonspontaneous, endothermic, and
endergonic process with activated formed complexes
structurally more ordered than the reactants. A negative deviation
from the Arrhenius behavior was observed for all oils
being the super-Arrhenius behavior more marked for
Arbequina oils that had the lowest TPC. Finally, the kineticthermodynamic
parameters allowed classifying oils according
to the binomial olive cultivar/total phenols level, being the
temperature acceleration factor and the Gibbs free energy
of activation at 160º C the most powerful discriminating
parameters.
Description
Keywords
Energy of activation Enthalpy of activation Entropy of activation Free Gibbs energy Monovarietal-blend oils thermal stability Rancimat test
Pedagogical Context
Citation
Veloso, Ana C.A.; Rodrigues, Nuno; Ouarouer, Yosra; Zaghdoudi, Khalil; Pereira, José A.; Peres, António M. (2020). A Kinetic-Thermodynamic Study of the Effect of the Cultivar/Total Phenols on the Oxidative Stability of Olive Oils. JAOCS, Journal of the American Oil Chemists' Society. ISSN 0003-021X. 97, p. 625-636