Absolute kinetics of peroxidation and antioxidant protection of intact triglyceride vegetable oils.

To verfy their difference from isolated fatty acids, the absolute kinetics of peroxidation was studied for seven triglyceride-based oils of olive (OLI-1, OLI-2), high-oleic sunflower (SUN-HO), high-oleic and high-linoleic safflower (SAF-HO, SAF-HL) grapeseed (GRA) and borage (BOR), by oxygen uptake monitoring, using 2,6-di- tert -butyl-4-methoxyphenol and 2,2,5,7,8-pentamethyl-6-chromanol as reference inhibitors. Propagation constants (k p /M−1 s−1 at 303 K in PhCl) were respectively 34.8 ± 2.3, 35.1 ± 1.8, 40.6 ± 5.5, 36.0 ± 7.7, 160.8 ± 5.1, 145.1 ± 24.5, 275.1 ± 63.8, while oxidizability responded to empirical equation k p (2 k t)-½/M-½s-½ = 1.63 × 10−3[allyl >CH 2 /M] + 1.82 × 10−2[bisallyl >CH 2 /M], based on fatty acids residues assessed by GC–MS. Peroxidation kinetics was markedly different from that of isolated fatty acids. The H-bond basicity of all oils was measured by FT-IR affording Abraham's βH 2 values in the range 0.55 ± 0.03. H-bonding explained the protection of oils measured for seven reference phenolic antioxidants, except for the catechols quercetin and caffeic acid phenethyl ester, which were 2-to-4-folds more effective than expected, supporting a proposed different mechanism. • k p and 2 k t constants for triglycerides differ from those of their main fatty acids. • MUFA-rich triglycerides oxidize 40-folds faster than their isolated MUFAs. • A linear empirical equation predicted oxidizability from FAME analysis (r 2 = 0.992). • Protection and k i nh for antioxidants were explained by H-bonding to triglycerides. • Catechols quercetin and CAPE gave exceptional protection via different mechanisms. [ABSTRACT FROM AUTHOR]