Study of thermal and photo-oxidation mechanisms of edible oils for future improvement

概要

⽣物産業創⽣科学専攻 ⾷品機能分析学
博⼠課程後期３年 Halida Rahmania (C0AD1305)

Study of thermal and photo-oxidation mechanisms of edible oils for future
improvement
⾷⽤油の熱酸化および光酸化の機構解明に関する研究： さらなる品質向上を⽬指して
Halida Rahmania (C0AD1305) ⽣物産業創⽣科学専攻
[Background] The major issue with utilizing the benefits of edible oils is the occurrence
of oxidation, as it can significantly affect the appearance, taste, and flavor of the oils, as
well as potentially produce toxic substances. Therefore, it is crucial to understand the
detailed mechanisms that occur during thermal and photo-oxidation processes. The
objective of this study is to invesitgate the oxidation mechanisms under thermal and
photo-oxidation on several edible oils, including rice bran oil (RBO), soybean oil (SO),
and rapeseed oil (RPO). Additionally, we evaluated the primary oxidation products
(triacylglycerol hydroperoxide; TGOOH) and secondary oxidation products (aldehydes),
as well as the activity of antioxidant agents such as γ-oryzanol (OZ) and vitamin E.
[Material and Method] Several edible oils (RBO, SO, RPO) were exposed to various
oxidation condition: 1) thermal oxidation at 40°C for 17 days to simulate harsh storage
conditions and 2) photo-oxidation under 1000 lx for 3 months at room temperature to
imitate daily storage conditions. The peroxide value (POV) was determined before and
after oxidation using a titration method (JOCS 2.5.2), and the levels of primary and
secondary oxidation products, such as TGOOH and aldehydes, were analyzed using LCMS/MS. Additionally, the decline in antioxidant (γ-oryzanol (OZ) and Vitamin E) levels
during oxidation was monitored by measuring their concentration using HPLC.
[Discussion] Under thermal oxidation, RBO showed superior stability compared to other
oils based on PoV profile and TGOOH/TG ratio. The stability of RBO during thermal
oxidation may be attributed to its fatty acid composition, specifically the presence of high
levels of oleic acid, low levels of linoleic acid, and low levels of α-linolenic acid. We also
found that OZ played significant role on maintaining stability under thermal oxidation1. On
the other hand, the oil stability under photo-oxidation according to PoV profile was almost
similar among the oils. Surprisingly, the TGOOH/TG ratio under photo-oxidation was not
following the PoV profile, while PoV showed a similar profile among the oil under photooxidation, the TGOOH/TG profile showed a clear gap. The aldehyde profiles (as
secondary oxidation products) were later evaluated to provide a better understanding on
fatty acid oxidation process. Under thermal oxidation, the aldehyde profile showed similar
profile TGOOH/TG, which also resembles the PoV profile. Besides, under photo-oxidation,
the aldehyde profile was only similar with TGOOH/TG profile but not the PoV. We
assumed that under photo-oxidation, the mono-, di-, or even tri- hydroperoxide were
produced while under thermal oxidation most of the hydroperoxide products were in
mono- type. For oil evaluation, we suggested that PoV profile might not be enough to
evaluate the oils stability under photo-oxidation, as the primary and secondary oxidation
profile cannot be reflected on PoV profile. Additional analysis (i.e., evaluation of primary
and secondary oxidation products) might be needed to comprehensively evaluate the oil
stability under photo-oxidation.
1) Rahmania, et al., Sci. Reports, 2020, 10, 14091. ...