Effects of infrared heat treatment on the active ingredients and comprehensive antioxidant level of Camellia seed oil

The purpose of this study is to investigate the internal relationship between the active components of Camellia oleifera seed oil and oxidation stability, as well as to comprehend the active component change after heat treatment. The Camellia oleifera seed oil was obtained by hydraulic pressing after heat treatment at different temperatures and time. A systematic analysis was implemented for the oxidation induction time, fatty acid composition, Maillard products, polyphenols, sterols, squalene, and tocopherol. The oxidation induction time was detected by Racimat method. The fatty acid composition was measured by GC (gas chromatography). The total phenol content was then determined by the Folin-Ciocalteu. The antioxidant capacity was then evaluated by the ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)), DPPH (2,2-diphenyl-1-picrylhydrazyl), and FRAP (ferricion reducing antioxidant power), iln order to analyze the correlation between total pheno content and antioxidant capacity. The determination contents of Maillard products were DPPH, the content of 5-HMF (5-hydroxymethyl furfural), MGO (methylglyoxal), and 3-DG (3-deoxyglucosone), and the correlation of DPPH, the content of 5-HMF, MGO, and 3-DG. The content of β-sitosterol and squalene were determined by GC, while the content of tocopherol was determined by high performance liquid chromatography (HPLC). The evaluation model was then constructed for the comprehensive antioxidant level of camellia seed oil using principal component analysis (PCA). There were differences in the comprehensive antioxidant level under different heat treatments. The results showed that the oxidation induction time decreased and then increased with the increase of temperature after heat treatment, where the maximum and minimum increased by 47.05% and decreased by 36.02%, respectively, compared with the control. Unsaturated fatty acids (UFA) were the highest percentage of the fatty acid composition, with oleic acid predominating. Specifically, the UFA was more likely to be oxidized than saturated fatty acids (SFA) during heat treatment. The total phenolic content increased with the increasing temperature. The highest total phenolic content was (121.55±3.22) μg/g, which was 7.12 times higher than that of the blank. The free radical scavenging was highly significantly correlated with the content (P<0.01), where the correlation coefficients r with ABTS, FRAP, and DPPH were 0.995, 0.993, and 0.956, respectively. The DPPH radical scavenging of the Maillard product first decreased and then increased with the increasing temperature up to (90.37±3.52) μg/g, 2.31 times higher than that of the control. The contents of 5-HMF, MGO and 3-DG decreased and then increased with the increasing temperature, with the highest values being 1.69, 7.19 and 4.27 times higher than those of the control, respectively. In addition, the DPPH radical scavenging capacity was significantly and positively correlated with the 5-HMF, 3-DG and MGO with correlation coefficients r of 0.705, 0.826, and 0.913, respectively.α-tocopherol was the most common form of tocopherol found in the camellia seed oil. The non-polar fraction contained 1.13, 1.03, and 1.25 times more β-sitosterol, squalene, and α-tocopherol than the blank control after heat treatment. The temperature was positively correlated with the β-sitosterol, which was significantly negatively correlated with the squalene, and significantly positively correlated with the α-tocopherol in the correlation analysis. Therefore, heat treatment posed a significant effect on the comprehensive antioxidant level of camellia seed oil. Four comprehensive indicators were optimized for the antioxidant capacity evaluation of PCA from nine indicators. The contribution rate of the first principal component was 50.775%, indicating the feedback of the total phenolic content of polar components, Maillard products, and oxidation induction time on the overall antioxidant capacity. The contribution rate of the second principal component was 18.513%, and the fourth principal component was 7.425%. The two principal components represented the nonpolar component squalene, β-sitosterol, and α-tocopherol on the overall antioxidant capacity. The contribution rate of the third principal component was 12.421%, indicating the feedback of the proportion of unsaturated fatty acids to the overall antioxidant capacity. The cumulative variance contribution rate of the first four principal components was 89.134% (>85%), including the most sample information. The comprehensive evaluation model showed that there was a greater weight of antioxidant capacity in the polar components (total phenols, and Maillard products) after heat treatment, compared with the non-polar components. In the increase of heat treatment temperature, the comprehensive antioxidant capacity of Camellia seed oil depended mainly on the non-polar components before 110 ℃, while the polar components played a major role in the comprehensive antioxidant capacity after 110 ℃. Compared with the untreated oil, the moderate heat treatment can be expected to change the content of active substances and antioxidant capacity in the camellia oleifera seed oil, thereby regulating the oxidative stability of the oil. The finding can provide the data support to investigate the thermal oxidation stabilization for the selection of processing parameters in camellia seed oil.