RESUMEN
The aim of the study was to analyze the influence of mullein flower extract addition on the oxidative stability and antioxidant activity of cold-pressed oils with a high content of unsaturated fatty acids. The conducted research has shown that the addition of mullein flower extract increases the oxidative stability of oils, but its addition depends on the type of oil and should be selected experimentally. In rapeseed and linseed oil, the best stability was found for samples with 60 mg of extract/kg of oil, while in chia seed oil and hemp oil, it was found with 20 and 15 mg of extract/kg of oil, respectively. The hemp oil exhibited the highest antioxidant properties, as evidenced by an increase in the induction time at 90 °C from 12.11 h to 14.05 h. Additionally, the extract demonstrated a protective factor of 1.16. Oils (rapeseed, chia seed, linseed, and hempseed) without and with the addition of mullein extract (2-200 mg of extract/kg of oil) were analyzed for oxidative stability, phenolic compounds content, and antioxidant activity using DPPH⢠and ABTSâ¢+ radicals. After the addition of the extract, the oils had from 363.25 to 401.24 mg GAE/100 g for rapeseed oil and chia seed oil, respectively. The antioxidant activity of the oils after the addition of the extract ranged from 102.8 to 221.7 and from 324.9 to 888.8 µM Trolox/kg for the DPPH and ABTS methods, respectively. The kinetics parameters were calculated based on the oils' oxidative stability results. The extract increased the activation energy (Ea) and decreased the constant oxidation rate (k).
RESUMEN
The aim of the study was to analyse the chemical composition and oxidation stability of selected cold-pressed oils and oil mixtures. The oils were tested for their initial quality, fatty acid composition, total phenolic compounds, DPPH, and ABTS free radical scavenging activity. The Rancimat method was used to assess oxidative stability. The obtained results were subjected to principal component analysis (PCA) to determine the influence of selected chemical properties on the oxidative stability of the oil. It has been found that different factors of oil quality influence the stability of cold-pressed oils. The highest correlation coefficient was noted between the induction time, peroxide value, and TOTOX indicator (r = 0.89). Fatty acid composition, including the percentage of SFA, MUFA, PUFA, and the ability to scavenge ABTS captions radicals, did not significantly affect the oxidative stability of the oils. Black cumin seed oil was the most resistant to the oxidation processes in the Rancimat apparatus, mainly due to the high content of phenolic compounds (384.66 mg GAE/100 g). On the other hand, linseed oil and its mixtures were the least stable. Their fatty acid composition was dominated by a polyunsaturated α-linolenic fatty acid, significantly reducing the antioxidant resistance.
RESUMEN
One of the commonly used food preparation methods is frying. Fried food is admired by consumers due to its unique taste and texture. Deep frying is a process of dipping food in oil at high temperature, usually 170-190 °C, and it requires a relatively short time. The aim of this study was to analyze the thermo-oxidative changes occurring during the deep frying of products such as potatoes and tofu in cold pressed rapeseed oils and palm olein. Cold pressed rapeseed oil from hulled seeds (RO), cold pressed high oleic rapeseed oil from hulled seeds (HORO), and palm olein (PO) (for purposes of comparison) were used. Characterization of fresh oils (after purchase) and oils after 6, 12, and 18 h of deep frying process of a starch product (potatoes) and a protein product (tofu) was performed. The quality of oils was analyzed by determining peroxide value, acid value, p-anisidine value, content of carotenoid and chlorophyll pigments, polar compounds, smoke point, color (CIE L*a*b*), fatty acids content and profile, calculation of lipid nutritional quality indicators, and oxidative stability index (Rancimat). Cold pressed high oleic rapeseed oil was more stable during deep frying compared to cold pressed rapeseed oil, but much less stable than palm olein. In addition, more thermo-oxidative changes occurred in the tested oils when deep frying the starch product (potatoes) compared to the deep frying of the protein product (tofu).
RESUMEN
The aim of this study was to compare the oxidative stability of linseed oil using the pressure differential scanning calorimetry (PDSC) and Rancimat methods, and to determine the kinetic parameters of linseed oil oxidation. Five cold pressed linseed oils were oxidized at different temperatures under PDSC (90-140 °C) and Rancimat (70-140 °C) test conditions. The oxidative stability of the linseed oils was calculated based on induction times (PDSCτmax, Rancimat τon), the Arrhenius equation and activated complex theory, frequency factors (Z), the reaction rate coefficient (k) for all temperatures, activation energies (Ea), Q10 numbers, activation enthalpies (∆H++), and activation entropies (∆S++). The PDSC method was more convenient for the determination of the induction time of linseed oils than the Rancimat method. During oxidation measurement by Rancimat method, the linseed oil polymerized, which affected the measurements. The reaction rate coefficient increased with rising temperature during measurement by both methods. The activation energy values of linseed oil oxidation using the PDSC and Rancimat methods ranged from 93.14 to 94.53 and 74.03 to 77.76 kJ mol-1, respectively. The Q10 , ∆H++, and ∆S++ values for the analyzed linseed oils were between 2.11-2.13, 90.54-91.30 kJ mol-1, -33.20 to -30.90 J mol K-1 calculated by PDSC measurements, and 2.23-2.32, 71.03-74.76, -59.42 to -49.08 J mol K-1 by Rancimat measurements, respectively.
