Abstract
Changes in antioxidant properties and degradation of bioactives in palm oil (PO) and rice bran oil (RBO) during deep-frying were investigated. The alpha (α)-tocopherol, gamma (γ)-tocotrienol and γ-oryzanol contents of the deep-fried oils were monitored using high performance liquid chromatography, and antioxidant activity was determined using 2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging activity. Results revealed that the antioxidant activity of PO decreased significantly (p < 0.05), while that of RBO was preserved after deep-frying of fries. As expected, the concentration of α-tocopherol in PO and γ-tocotrienol in both PO and RBO decreased significantly (p < 0.05) with increased frying. Results also showed that γ-tocotrienol was found to be more susceptible to degradation compared to that of α-tocopherol in both PO and RBO. Interestingly, no significant degradation of α-tocopherol was observed in RBO. It is suggested that the presence of γ-oryzanol and γ-tocotrienol in RBO may have a protective effect on α-tocopherol during deep-frying.
Highlights
Vegetable oils are generally known to be healthy, due to being high in unsaturated fatty acid and other various phytochemical compounds
Free radical scavenging activity utilizing the diphenyl-1-picryl hydrazyl (DPPH) radical was done in determining the antioxidant capacity of the oils, due to its simplicity and wide use in antioxidant research
Results presented here are in line with that of a previous study conducted by Gomez-Alonso et al [28], where the reduction of antioxidant activity of olive oil correlated well with the number of deep-frying cycles
Summary
Vegetable oils are generally known to be healthy, due to being high in unsaturated fatty acid and other various phytochemical compounds. Rice bran oil has been reported to be an excellent source of antioxidants, such as tocopherols, tocotrienols and oryzanols [4]. Several in vivo studies revealed the existence of the relationship between deep-frying oil quality intake with oxidative stress level. Like PO and RBO, contain bioactive compounds that can protect lipids from oxidation, the reaction can still occur during deep-frying, which results from the degradation of the bioactive compounds, as affected by exposure to high temperature [3,13]. This study was conducted to evaluate the radical scavenging capacity and prominent bioactive compounds (α-tocopherol, γ-tocotrienol and γ-oryzanol) in PO and RBO, as well as to examine their degradation kinetic during the deep-frying of French fries
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