A Kinetic‐Thermodynamic Study of the Effect of the Cultivar/Total Phenols on the Oxidative Stability of Olive Oils

Abstract

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 kinetic‐thermodynamic 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 160 °C the most powerful discriminating parameters.

Kinetic-thermodynamic study of the oxidative stability of Arbequina olive oils flavored with lemon verbena essential oil

“…Table 2 clearly shows that the OS is significantly influenced by both factors, with significant decrease (P-value < 0.05) when the temperature rise (from 110 to 150 • C, for all EO flavoring levels) as well as with the increase of the EO flavoring level (from 0.0 to 0.4% EO, except for 150 • C), pointing out that the oil lipid oxidation is faster at higher temperatures and when higher amounts of EO were added (in-line with the results found for the PV, K 232 and K 268 but in disagreement with the TRC). The observed temperature decreasing effect is in accordance with the literature data for olive oils (Farhoosh & Hoseini-Yazdi, 2014;Heidarpour & Farhoosh, 2018;Veloso et al, 2020). Similar decreasing trends were also reported found for olive oils flavored with lemon, dried chili pepper, hot pepper, rosemary, sweet lime/orange, oregano or basil (Baiano et al, 2009;Bobiano et al, 2019;Caporaso, Paduano, Nicoletti, & Sacchi, 2013;Khemakhem et al, 2015).…”

“…Similar decreasing trends were also reported found for olive oils flavored with lemon, dried chili pepper, hot pepper, rosemary, sweet lime/orange, oregano or basil (Baiano et al, 2009;Bobiano et al, 2019;Caporaso, Paduano, Nicoletti, & Sacchi, 2013;Khemakhem et al, 2015). Opposite findings (i.e., higher OS values for higher content of the flavoring agent) were also reported in the literature, which are in general linked to higher TRC values (Ayadi et al, 2009;Farhoosh & Hoseini-Yazdi, 2014;Sousa et al, 2015;Veloso et al, 2020). Thus, once again, based on the contradictory literature data, no clear trend can be theorized regarding the positive/negative effect of oils' flavoring process on their OS.…”

“…The oxidative stability (OS) of the oils at different temperatures (110,120,130,140 and 150 • C) were assessed using the Rancimat method (Rancimat 743 apparatus from Metrohm CH, Switzerland) following the methodology previous described by Veloso et al (2020). This experimental data allows to calculate the kinetic-thermodynamic parameters.…”

“…A kinetic-thermodynamic approach was applied, based on the OS experimental data recorded at different temperatures (110,120,130,140, 150 • C), under Rancimat test conditions (Ciemniewska-Żytkiewicz et al, 2014;Farhoosh et al, 2008;Farhoosh & Hoseini-Yazdi, 2014;Heidarpour & Farhoosh, 2018;Mahdavianmehr et al, 2016;Trapani et al, 2017;Malvis et al, 2019;Veloso et al, 2020). This methodology allowed to calculate (Veloso et al, 2020): i. The temperature coefficient T C ( • C − 1 ), equal to the slope of the linear regression line established between the decimal logarithmic of the OS (in h) and the temperature T (in • C); ii.…”

“…The lipid oxidation was further evaluated based on the activated complex theory, aiming to establish, for the first time, a kinetic-thermodynamic insight regarding the impact of the flavoring on the oils' oxidation process. This kinetic-thermodynamic approach has been previously used, for example, to assess different olive oils' stabilities and to compare them with those of other vegetable oils evaluating, in some cases, the effect of indigenous antioxidant compounds or fatty acid composition, to evaluate the oxidation kinetics of purified compounds, to establish an olive oil adulteration index for recognizing adulterations with palm olein and sunflower oil or to develop unsupervised/supervised classification models for monovarietal and blend olive oils discrimination according to the cultivar/total phenols content (Ciemniewska-Żytkiewicz, Ratusz, Bryś, Reder, & Koczoń, 2014;Farhoosh & Hoseini-Yazdi, 2014;Farhoosh, Niazmand, Rezaei, & Sarabi, 2008;Gharby et al, 2016;Heidarpour & Farhoosh, 2018;Mahdavianmehr, Farhoosh, & Sharif, 2016;Ostrowska-Ligeza et al, 2010;Veloso et al, 2020). In this context, the main aim of this study was the kinetic-thermodynamic evaluation of the lipid oxidation of cv.…”