Synergic Antioxidant Effects of the Essential Oil Component γ-Terpinene on High-Temperature Oil Oxidation

The synergic antioxidant activity of γ-terpinene with α-tocopherol, its synthetic analogue 2,2,5,7,8-pentamethyl-6-chromanol (PMHC), BHT, TBHQ, and catechol was studied by measuring the O2 uptake and the hydroperoxide formation in stripped sunflower oil at 130 °C. Although γ-terpinene was inactive when used alone, it prolonged, in a concentration-dependent manner, the protecting activity of α-tocopherol and of PMHC, while it had no effect on BHT, TBHQ, and catechol. Mechanistic studies performed with alkylnitroxides hydroxy-TEMPO and acetamido-TEMPO, used as molecular probes, suggested that γ-terpinene generates hydroperoxyl (HOO•) radicals, that are responsible for the reduction of the tocopheroxyl radical by a H atom transfer. Experiments on commercial sunflower oil showed that γ-terpinene was able to prolong the induction time due to endogenous tocopherols, demonstrating that this terpene is a promising natural antioxidant for food applications at high temperature.