Foram realizados quatro ensaios para verificação da atividade antioxidante de extratos etanólicos de alecrim (A) e orégano (O) comparados com os antioxidantes sintéticos TBHQ e BHA+BHT. Os resultados de atividade antioxidante do teste usando sistema modelo diferiram das respostas do teste acelerado em estufa. Nos ensaios em estufa os valores de peróxido e absortividade em 232nm dos óleos de soja, adicionados de 25, 50, 75, 100 e 200mg TBHQ. Kg-1, foram menores do que os dos óleos adicionados dos extratos de orégano (O) (1000mg.Kg-1), de alecrim (A) (500mg.Kg-1) ou da mistura deles (A + O). Todos os tratamentos retardaram a oxidação do óleo, entretanto os extratos naturais não atingiram a eficiência do TBHQ, mas foram tão efetivos quanto a mistura BHA+BHT. A adição dos extratos naturais a doses reduzidas de TBHQ não melhorou a eficiência em retardar a oxidação.

Four experiments were conducted to measure the antioxidant activity of ethanol extracts of rosemary and oregano compared with synthetic antioxidants such as TBHQ and BHA/BHT. The antioxidant activity was determined and results differed from those of the Oven test at 63º C. Peroxide values and absorptivities at 232 nm of soybean oil under Oven test were lower in treatments with 25, 50, 75, 100 and 200 mg.Kg-1 TBHQ than in treatments with 1000 mg.Kg-1 oregano extract (O), 500 mg.Kg-1 rosemary extract (R) and their mixture R+O. All the treatments were effective in controlling the thermal oxidation of oils; the natural extracts were as effective as BHA+BHT and less effective than TBHQ. The natural extracts were mixed with 25, 50, 75 and 100 mg.Kg-1 TBHQ and then added to the oil. No improvement in antioxidative properties was observed. The best antioxidant concentration could be determined from polynomial regression and quadratic equation from the experimental data.