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

Abstract

Arbequina extra-virgin olive oils were flavored with lemon verbena (Aloysia citrodora) essential oil (0.1-0.4%, w/ w), being evaluated quality parameters (free acidity, peroxide value, UV-extinction coefficients), oxidative stability, antioxidant and total reducing capacity. The kinetic-thermodynamic nature of the lipid oxidation was evaluated by Rancimat (110-150 • C). The essential oil addition promoted the antioxidant and total reducing capacities but, unfortunately, increased primary and secondary related quality parameters. Moreover, flavoring decreased the oils' oxidative stability. The kinetic-thermodynamic data showed that unflavored oils had significantly lower oxidation reaction rates (0.055-0.06492 h − 1 ), more negative temperature coefficient (− 0.0268 • C − 1 ), higher temperature acceleration factor (1.852), greater activation energy (82.7 kJ mol − 1 ) and frequency factor (10.9 × 10 9 h − 1 ), higher positive enthalpy of activation (79.4 kJmol -1 ), lower negative entropy of activation (− 131.8 J mol − 1 K − 1 ) and greater positive Gibbs free energy of activation (129.95-135.23 kJ mol − 1 ), showing that oils' oxidation was negatively influenced by the essential oil incorporation. Overall, oxidation had a non-spontaneous, endothermic and endergonic nature. Finally, olive oils could be satisfactorily classified (principal component and linear discriminant analysis) according to the flavoring level, using qualityantioxidant-stability or kinetic-thermodynamic datasets. The latter showed a less predictive performance, although ensuring the full discrimination of unflavored from flavored oils.

Kinetic study of the microwave‐induced thermal degradation of cv. Arbequina olive oils flavored with lemon verbena essential oil

“…For the PV, the results showed a slight decreasing trend with the increase of the flavoring level allowing to admit that the addition of the EO could have a protective effect against the olive oils' oxidative degradation and rancid formation, minimizing the reaction with free oxygen. This trend was contrary to that previously observed by Cherif et al (2021) for cv. Arbequina also flavored with lemon verbena EO or in other studies (Baiano et al, 2009; Caponio et al, 2016), but similar to the trends reported by other researchers (Bobiano et al, 2019; Tarchoune et al, 2019) for different flavoring agents (e.g., fruits, leaves, dry or fresh spices, EO, or aromatic herbs).…”

“…Arbequina oils' flavoring did not influence the FA, which was not affected by the different microwave heating times evaluated. These outcomes are in agreement with the previous findings of the research team (Cherif et al, 2021) and in line with the findings of Malheiro et al (2009), Cerretani et al (2009), and Yan et al (2020). Recently, Kishimoto (2019) reported that the FA of olive oils was not affected by the microwave heating time, except when an intense microwave heating was applied (i.e., heating at 500 W, reaching a temperature of 207°C), which led to an FA increase over the heating procedure.…”

“…Lemon verbena EO was chosen due to its well‐documented richness in polyphenols (Ishkeh et al, 2019; Rocha et al, 2019). The volatile composition of the lemon verbena EO was previously reported by Cherif et al (2021) and was in line with the literature data, and no sign of deterioration was visible.…”

“…Flavoring resulted in a linear increase of the TPC (112–160 mg GAE/kg oil, R ‐Pearson = +0.9870) and of the TCC (2.19–2.56 mg lutein equivalents/kg oil, R ‐Pearson = +0.9611), but not so evident for chlorophyll content (2.32–3.19 mg pheophytin equivalents/kg oil, R ‐Pearson = +0.8238). Previously, Cherif et al (2021) reported a decrease of the OS and an increase of both TPC and DPPH with the increase of the lemon verbena EO flavoring level in cv. Arbequina oils.…”

“…Recently, it was observed that flavoring cv. Arbequina oils with lemon verbena EO increased the antioxidant and total reducing capacities but decreased the oxidative stability (OS) (Cherif et al, 2021), and it was found that the oils' oxidation at high temperatures (110–150°C) had a nonspontaneous, endothermic, and endergonic nature. In this sense, several parameters were evaluated namely the free acidity (FA), peroxide value (PV), extinction coefficients at 232 and 270 nm, K 232 and K 270 , as well as the radical scavenging antioxidant activity, total phenols content (TPC), total carotenoids content (TCC), and chlorophyll content.…”