Changes in antioxidant activity and free radical scavenging potential of rosemary extract and tocopherols in isolated rapeseed oil triacylglycerols during accelerated tests

The effect of rosemary extract and tocopherols (-T) on the oxidative stability of rapeseed oil triacylglycerols (TAG) was evaluated by two instrumental tests: Rancimat® - measuring the generated carboxylic oxidation products and Oxidograph® - the measurement of oxygen absorption rate. Induction time and potential of the antioxidants to quench 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical were used as major indicators of antioxidative potential of antioxidants used. The rosemary extract was a more effective antioxidant in the rapeseed oil TAG than α-, γ-, δ-tocopherols alone, and more effective than a homologous mixture composed of α-, γ-, δ-tocopherol, and butylated hydroxytoluene. Capacity to quench of DPPH radicals was measured before oxidation tests and when the end of stability was established. After the accelerated oxidation of systems consisting of TAG and antioxidants in Oxidograph and Rancimat, the ability to quench of the DPPH radical remained even after the end of induction time. The same systems oxidized in Rancimat possessed higher activity of quenching DPPH radicals than fresh prepared. This trend was observed in all samples with exception of the one to which α-T was added.