Open Life Sciences 2020; 15: 606–618 Research Article Dani Dordevic, Ivan Kushkevych*, Simona Jancikova, Sanja Cavar Zeljkovic, Michal Zdarsky, Lucia Hodulova Modeling the effect of heat treatment on fatty acid composition in home-made olive oil preparations https://doi.org/10.1515/biol-2020-0064 refined olive oil in PUFAs, though a heating temperature received May 09, 2020; accepted May 25, 2020 of 220°C resulted in similar decrease in MUFAs and fi Abstract: The aim of this study was to simulate olive oil PUFAs, in both extra virgin and re ned olive oil samples. ff fi use and to monitor changes in the profile of fatty acids in The study showed di erences in fatty acid pro les that home-made preparations using olive oil, which involve can occur during the culinary heating of olive oil. repeated heat treatment cycles. The material used in the Furthermore, the study indicated that culinary heating experiment consisted of extra virgin and refined olive oil of extra virgin olive oil produced results similar to those fi samples. Fatty acid profiles of olive oil samples were of the re ned olive oil heating at a lower temperature monitored after each heating cycle (10 min). The out- below 180°C. comes showed that cycles of heat treatment cause Keywords: virgin olive oil, refined olive oil, saturated significant (p < 0.05) differences in the fatty acid profile fatty acids, monounsaturated fatty acids, polyunsatu- of olive oil. A similar trend of differences (p < 0.05) was rated fatty acids, cross-correlation analysis found between fatty acid profiles in extra virgin and refined olive oils. As expected, the main differences occurred in monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs).Cross-correlation 1 Introduction analysis also showed differences between the fatty acid profiles. The most prolific changes were observed between Olive oil, especially extra virgin olive oil, is the major - the control samples and the heated (at 180°C) samples of source of fat in the so called Mediterranean diet that very often has positive health benefits. The reason for this attribute is mainly the lower content of saturated fatty acids (SFAs) and the higher content of polyphenolic * Corresponding author: Ivan Kushkevych, Department of compounds. The fatty acid profile is important for the Experimental Biology, Faculty of Science, Masaryk University, quality and stability of oils. Oleic acid (C18:1) is a Kamenice 753/5, 62500, Brno, Czech Republic, monounsaturated fatty acid (MUFA), and it is more - e mail: [email protected] ( ) Dani Dordevic: Department of Plant Origin Foodstuffs Hygiene and stable than polyunsaturated fatty acids PUFAs . PUFAs Technology, Faculty of Veterinary Hygiene and Ecology, University of are usually present in lower percentages in olive oil Veterinary and Pharmaceutical Sciences Brno, 61242, Brno, Czech [1–4]. Cold-pressed edible plant oils, such as extra virgin Republic; Department of Technology and Organization of Public olive oil, are usually added to different salads. This may Catering, South Ural State University, 454080, Chelyabinsk, Russia mean that they are consumed without heat treatment. Simona Jancikova, Michal Zdarsky, Lucia Hodulova: Department of Recently, these types of edible plant oils have been used Plant Origin Foodstuffs Hygiene and Technology, Faculty of ff Veterinary Hygiene and Ecology, University of Veterinary and for cooking, as part of di erent culinary techniques and Pharmaceutical Sciences Brno, 61242, Brno, Czech Republic recipes. In this case, even cold-pressed edible plant oils Sanja Cavar Zeljkovic: Department of Genetic Resources for are heated at high temperatures. Such heating processes Vegetables, Centre of the Region Haná for Biotechnological and can affect the fatty acid profile of these oils, for instance, Agricultural Research, Medicinal and Special Plants, Crop Research heating increases the trans fatty acids, which have Institute, 78371, Olomouc, Czech Republic; Department of ff [ ] Phytochemistry, Centre of Region Haná for Biotechnological and potentially harmful health e ects 5 . Agricultural Research, Faculty of Science, Palacky University, 78371, Different culinary conditions, especially the tem- Olomouc, Czech Republic perature and the time of heat processing, can influence Open Access. © 2020 Dani Dordevic et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License. Olive oil fatty acid changes during heating cycles 607 the fatty acid composition of oils [6,7]. The type of oil below the allowed limits proposed by Codex Alimentarius also influences the changes in oil and its stability during (refined olive oil: PV < 5 mEq of active oxygen/kg oil, FFAs heat treatment due to difference in fatty acid profiles. < 0.3 mg KOH/g oil; cold-pressed olive oil: PV < 20 mEq of SFAs are more stable than unsaturated fatty acids, and active oxygen/kg oil, FFAs < 0.8 mg KOH/g oil; the similarly MUFAs are more stable when compared to standard limits were written on the labeling of extra virgin PUFAs [8]. The advantage of olive oil is the higher olive oil samples). Part of the olive oil sample was taken to content of MUFA (oleic acid), and this property gives serve as a control sample without heat treatment. The olive oil a higher level of oxidative stability than that of remainder of the olive oil sample (300 mL) was heated in other edible plant oils with a higher content of PUFAs. open glass tubes (250 mL glass tubes used for Kjeltec 2300 Cold-pressed olive oil or extra virgin olive oil has the digestion) at 180°C and 220°C, in an oven (Professional additional advantage of high levels of polyphenols, Ovens GARB-IN, Model:23 GM). The heat treatment lasted tocopherols, and carotenoids [4,9,10]. The fatty acid for 10 min and was repeated for three cycles (3 × 10 min). profile of olive oil is influenced by olive variety, weather, Between each cycle, part of the olive oil sample (100 mL) environment, and harvest conditions, as well as agro- was taken for analysis (of fatty acid composition) and the nomic and technologic factors [11,12]. remainder was heated again. Between heat cycles, the Olive oil, especially extra virgin olive oil (cold- samples were allowed to cool for 20 min. pressed olive oil), is considered beneficial for the health of consumers due to the presence of phenolic com- pounds, such as hydroxytyrosol (which improves radical stability) and oleuropein. Such compounds are involved 2.2 Fatty acid composition in inhibiting inflammatory processes. They additionally prevent liver damage by reducing oxidative stress, mito- Fatty acids were methylated with 0.5 M NaOMe/MeOH chondrial dysfunction, endoplasmic reticulum stress, and solution and extracted into n-hexane. The resulting fatty insulin resistance [13,14]. acid methyl esters (FAMEs) were analyzed by the gas Deep frying is a frequently used culinary practice. chromatography–mass spectrometry method on the The temperature during deep frying is usually around Agilent system (GC 7890 A; MSD 5975C series II) on a 180°C. This practice is popular among consumers since fused silica HP-5MS UI column (30 m × 0.25 mm × deep fried food usually have attractive sensory proper- 0.25 mm) and carrier gas He (1.1 mL/min).Thetemperature ties [15,16]. The legislation concerning the fatty acid was programmed at 40°C for 2 min, 10°C/min to 200°C, and profile of different olive oils is given in percentages, with finally 2°C/min to 250°C for 2 min. Post run of 15 min was set a key emphasis on oleic fatty acid (C18:1)[17]. at 310°C. The temperature of the injection port was 250°C and This study aimed to simulate home-based heat that of the detector was 280°C. Ionization was performed treatment of olive oil and to measure the changes in in the EI mode (70 eV).Identification was performed by the profile of fatty acids due to repeated heating cycles. comparison of retention times and mass spectra with authentic standards (Supelco. Merck KGaA, Darmstadt, Germany), and the results were presented as mg/mL. The results were calculated according to the official method 2 Materials and methods for fatty acid profile determination [18–20]. The successful separation of the evaluated FAMEs, including n-undecane 2.1 Heat treatment of olive oil samples that was used as an internal standard, is shown in Figure 1. The samples (n = 10) used in the experiment consisted of refined olive oils (n = 4) and multivariate extra virgin olive oils (n = 6; olive oil purchased in retail markets in 2.3 Antioxidant profile the Czech Republic, originating from Spain and Greece). Each purchased olive oil had around 18 months for the Chlorophyll, carotenoid, and polyphenol contents were expiration date. The purchased olive oil samples were measured in the samples of olive oil before (control packed in glass bottles (volume: from 0.5 to 1 L). The samples) and after three heating cycles at 180°C and labeling of the olive oil samples indicated that they had 220°C. All the samples were measured in triplicates to peroxide value (PV) and free fatty acid (FFA) content reduce the possibility of error. 608 Dani Dordevic et al. Figure 1: Chromatogram of FAME standards (Supelco). Carotenoid, polyphenol, and chlorophyll contents were WA, USA). Triplicate sampling was used in all data evaluated on a Cecil Instrument spectrophotometer calculations. Statistical significance (p < 0.05) was (CE7210). The wavelength for calculating carotenoids estimated by the analysis of variance. The Shapiro–Wilk was 445 nm. The cuvettes were rinsed with n-hexane to test was used to determine the results’ normality, whereas avoid mixing of samples. The carotenoid contents were Levene’s test was used to estimate the homogeneity of expressed as β-carotene. The quantification was done variances.