Synergic antioxidant activity of γ-terpinene with phenols and polyphenols enabled by hydroperoxyl radicals

Antioxidant interactions of gamma-terpinene with alpha-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, gamma-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/gamma-terpinene and CAPE/gamma-terpinene increased with gamma-terpinene concentration, while rate constants for radical-trapping were unchanged by gamma-terpinene, being 3.1 x 10(6) and 4.8 x 10(5) M(-1)s(-1) for PMHC and CAPE in chlorobenzene (30 degrees C). Using 3,5-di-tert-butylcatechol and 3,5-di-tert-butyl-1,2-bezoquinone we demonstrate that gamma-terpinene can reduce quinones to catechols enabling their antioxidant activity. The different synergy mechanism of gamma-terpinene with mono- and poly-phenolic antioxidants is discussed and its relevance is proven in homogenous lipids using natural alpha-tocopherol and hydroxytyrosol as antioxidants, calling for further studies in heterogenous food products.

Automated summary

The study demonstrates that gamma-terpinene can interact with mono- and polyphenolic antioxidants, synergistically regenerating chain-breaking antioxidants and exhibiting antioxidant activity. The different synergy mechanisms of gamma-terpinene with different types of antioxidants are discussed, highlighting its relevance in lipid oxidation and calling for further research in heterogeneous food products.