Inhibition Effect of Oryzanol on the Degradation of Tocopherol and the Oxidation Kinetic of Rice Bran Oils with Different Content of Oryzanol and Tocopherol

Abstract

The purpose of this study is to investigate the inhibitory effect of oryzanol on the degradation of tocopherol during heating of rice bran oil at 110 and 170 °C and the oxidation kinetics of rice bran oil. Results demonstrate the degradation of oryzanol and tocopherol in rice bran oils follow the first‐order kinetic models. The higher concentration of oryzanol has no inhibitory effect on the degradation of tocopherol when the concentration of tocopherol in rice bran oil is 500 mg kg−1. However, when the concentrations of tocopherol reach 1500 and 2000 mg kg−1, higher oryzanol concentration make the inhibitory effects on the degradation of tocopherol more pronounced. Compared with rice bran oils containing lower levels of tocopherol and oryzanol, rice bran oils containing higher levels of tocopherol and oryzanol have higher activation energy (Ea), activation enthalpy (ΔH), and activation entropy (ΔS) and a larger temperature acceleration factor (Q10), which indicate that higher levels of oryzanol and tocopherol promote the thermal oxidation of rice bran oil. Therefore, in the compound application of tocopherol and oryzanol in rice bran oil, the influence of its content on the thermal oxidation of oil should be fully considered. Practical Application: This study may be useful for the grain and oil industry because studies on the degradation kinetics of oryzanol and tocopherol during heating of rice bran oil and oxidation kinetics of rice bran oil are still lacking in the literature. The results of this study is valuable for predicting and evaluating the oxidation process and nutritional properties of rice bran oils under various thermal oxidation conditions.

An Insight into the Thermal Degradation Pathway of γ-Oryzanol and the Effect on the Oxidative Stability of Oil

“…γ-Oryzanol and its components exhibited conformity to the first-order kinetic model at different thermal treatment temperatures ( R 2 > 0.9) (Table S1). Similar observations have been documented in previous studies, which found that the degradation of γ-oryzanol during heating followed first-order kinetics. , …”

“…Similar observations have been documented in previous studies, which found that the degradation of γ-oryzanol during heating followed first-order kinetics. 11,35 According to the results shown in Table 2, it can be observed that with increasing temperature, the thermal degradation rate constant (K) of γ-oryzanol and its four components increased while the half-life (t 1/2 ) decreased. These results indicated that higher temperatures have a greater impact on the stability of γ-oryzanol.…”

“…32,33 Previously, several studies had been conducted on the thermal stability of γ-oryzanol. 11,12 However, the loss rates at elevated temperatures still exhibited differences. The main factors contributing to these differences were attributed to temperature variations and the diversity of oils.…”

“…The loss of γ-oryzanol in oil at high temperatures was attributed to the thermal degradation of γ-oryzanol itself, as well as the occurrence of lipid oxidation reactions generating free radicals during the heating process. γ-Oryzanol interrupted the chain propagation of the oxidation reaction by providing hydrogen atoms to free radicals, resulting in the loss of γ-oryzanol. , Previously, several studies had been conducted on the thermal stability of γ-oryzanol. , However, the loss rates at elevated temperatures still exhibited differences. The main factors contributing to these differences were attributed to temperature variations and the diversity of oils.…”

“…10 The molecular structure responsible for antioxidant activity is affected or damaged after the degradation of γ-oryzanol, which could influence the overall antioxidant activity. However, most studies have currently focused only on the thermal stability of γ-oryzanol as a whole, 11,12 without revealing its degradation products and thermal degradation pathways, as well as the impact of the generated degradation products on antioxidant capacity.…”