Antioxidant interactions of γ-terpinene with α-tocopherol mimic 2,2,5,7,8-pentamethyl-6-chromanol (PMHC) and caffeic acid phenethyl ester (CAPE), used as models, respectively, of mono- and poly-phenols were demonstrated by differential oximetry during the inhibited autoxidation of model substrates: stripped sunflower oil, squalene, and styrene. With all substrates, γ-terpinene acts synergistically regenerating the chain-breaking antioxidants PMHC and CAPE from their radicals, via the formation of hydroperoxyl radicals. The inhibition duration for mixtures PMHC/γ-terpinene and CAPE/γ-terpinene increased with γ-terpinene concentration, while rate constants for radical-trapping were unchanged by γ-terpinene, being 3.1 × 106 and 4.8 × 105 M-1s-1 for PMHC and CAPE in chlorobenzene (30 °C). Using 3,5-di-tert-butylcatechol and 3,5-di-tert-butyl-1,2-bezoquinone we demonstrate that γ-terpinene can reduce quinones to catechols enabling their antioxidant activity. The different synergy mechanism of γ-terpinene with mono- and poly-phenolic antioxidants is discussed and its relevance is proven in homogenous lipids using natural α-tocopherol and hydroxytyrosol as antioxidants, calling for further studies in heterogenous food products.
Keywords: 2,2,5,7,8-Pentamethyl-6-chromanol (PubChem CID 99479); 3,5-Di-tert-butylcatechol (PubChem CID 66099); 3,5-di-tert-butyl-1,2-benzoquinone (PubChem CID 24849680); Caffeic acid; Caffeic acid phenethyl ester (PubChem CID 5281787); Hydroxytyrosol; Hydroxytyrosol (PubChem CID 82755).; PubChem CID 14985); Quinones’ regeneration; Squalene; Squalene (PubChem CID 638072); Stripped sunflower oil; Styrene (PubChem CID 7501); Sunflower seed oil (PubChem SID 404771784); Synergy; Vitamin E (d-α-tocopherol; α-Tocopherol; γ-Terpinene; γ-Terpinene (PubChem CID 7461).
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