antioxidant effect of red quinoa carotenoid extract obtained by supercritical fluid extraction on soybean oil stabilization

Frying is the process of soaking food in hot oil in relationship with air and food at high temperature (around 140–190° C), during thermal processing, a set of chemical reactions such as hydrolysis, oxidation, thermal decomposition, and polymerization occurs (Keshavarz Moghadam And Moslehishad 2020). Quinoa (Chenopodium quinoa Willd.) is singled out as a food rich in antioxidants (Melini and Melini 2021). Colored quinoa cultivars have been demonstrated to be a good source of phenolics, flavonols, and betalains mainly contained in the quinoa hulls (Laqui-Vilca et al., 2018). The literature has reported the presence lutein and zeaxanthin in the seeds of three quinoa genotype (Multari et al., 2018).Carotenoids are unsaturated hydrocarbons and fat-soluble pigments, which are composed of 8 isoprene units. Thus, their chemical structure consists of ~40 carbon atoms (Mateos and García-Mesa 2006) which can quench singlet oxygen by their numerous conjugated double bonds. The degree of quenching increases as the number of the bonds rises in lutein, zeaxanthin, lycopene, astaxanthin, and isozeaxanthin (Kaur et al., 2015; Steenson and Min, 2000). Carbon dioxide, as the most common solvent used in the supercritical fuid extraction process, can pass through solids like a gas and dissolve substances in itself like a liquid. Therefore, the features of liquid solubility and gaseous permeability, as well as low viscosity under the supercritical conditions, make it possible for carbon dioxide to permeate the plant matrices. In addition, carbon dioxide can be easily separated from extractive materials without leaving toxic compounds in the extract (Salami et al., 2020). In this study, the antioxidant effect of carotenoid extract by supercritical fluid extraction method and commercial beta-carotene on the stabilization of soybean oil was investigated.

Carotenoid extract of red quinoa was extracted by supercritical fluid method with co-solvent 10% and 15% ethanol and then added to soybean oil with commercial beta-carotene at a concentration of 200 ppm. Samples were stored at 60 ° C for 8 days. Peroxide value (PV), conjugated diene (CD) and thiobarbituric acid (TBA) tests and colorimetry were measured to evaluate the effect of carotenoid extract and commercial beta-carotene on the stability of soybean oil.

With increasing storage time, the amount of peroxide in all samples containing antioxidants increased. All samples on the first day of storage had significantly less peroxide than the samples on the last day of storage (P <0.05). Samples containing carotenoid extract by supercritical fluid extraction method with the co-solvent of 10%, 15% ethanol had significantly less peroxide content in most storage days than samples containing commercial beta-carotene (P <0.05). The lowest amount of peroxide on the last day of storage with a value of 7.21 (meq / Kg fat) was related to the sample containing carotenoid extract with supercritical fluid extraction with 15% ethanol solvent. Samples containing beta-carotene and carotenoid extract by supercritical fluid extraction method with the co solvents of 10%, 15% ethanol increased the amount of conjugated diene value with increasing storage time. In general, there was a significant difference in all samples on the first and last day of storage (P <0.05). Samples containing carotenoid extract by supercritical fluid extraction method in most storage days, especially in the last days of storage, compared to samples containing commercial beta-carotene, had significantly less conjugated diene value (P <0.05), which could be due to its higher carotenoid content. On the last day of storage, the sample containing carotenoid extract by supercritical extraction method with the co-solvent of 15% ethanol with the amount of 16.032 mmol / L had the lowest and the sample containing commercial beta-carotene with the amount of 19.60 mmol / L had the highest amount of conjugated diene value. In the early days, the amount of thiobarbituric acid is low, but over time the primary oxidation products increase and begin to decompose, and the amount of this index increases and volatile aldehydes are formed. The amount of thiobarbituric acid in the samples increased with increasing storage time. Samples containing carotenoid extract with supercritical fluid extraction with 10% ethanol from the sixth day and samples containing beta-carotene and carotenoid extract with 15% ethanol on the last day had lower thiobarbituric acid levels than the previous day. Which was due to the oxidation of autooxidation products. Samples containing carotenoid extracts by supercritical fluid extraction method, due to their better antioxidant performance, had significantly lower thiobarbituric acid content than samples containing commercial beta-carotene (P <0.05). In all samples, the value of b * is higher than zero and positive and are in the yellow range and b * index of samples containing carotenoid extracts by supercritical fluid extraction method was higher than commercial beta-carotene due to the yellowing of carotenoid extracts added to oil (p <0.05). Index of a * samples containing commercial beta-carotene and carotenoid extract at a concentration of 200 ppm, there was no significant difference between samples containing commercial beta-carotene during storage at 60 ° C (p > 0.05). The parameter a * in most samples is lower than zero and negative, which may be due to changes in carotenoid pigments in the oil during storage. Carotenoid extracts by supercritical method with the co-solvent ethanol 10%, 15% due to turbidity and yellowish color reduced the transparency of oil samples, so they had significantly less L * than commercial beta-carotene samples (p <0.05).

In this study, red quinoa carotenoid extract was extracted using supercritical fluid with the co solvents of 10%, 15% and its antioxidant effect was compared with commercial beta-carotene at a concentration of 200 ppm on the stabilization of antioxidant-free soybean oil. The results of this study showed that the carotenoid extracts by the supercritical fluid extraction method performed better than commercial beta-carotene in reducing the amount of peroxide, conjugate diene and thiobarbituric acid. As a result, carotenoid extract was more effective in oxidative stabilization of soybean oil than commercial beta-carotene. b * index of samples containing carotenoid extracts by supercritical fluid extraction method was higher than commercial beta-carotene. The parameter a * in most samples was lower than zero and negative and the L * index of samples containing carotenoid extract by supercritical fluid extraction method was lower than commercial beta-carotene.