In vitro antioxidant analysis of supercritical fluid extracts from rosemary (Rosmarinus officinalis L.)

Different supercritical fluid extraction conditions were tested on rosemary leaves using a pilot-plant-scale extractor. Each of them provided two separated fractions which were characterized chemically by liquid chromatography–diode-array detection–mass spectrometry using electrospray in the positive mode. Twelve compounds were identified, including phenolic diterpenes and flavonoids. Owing to the lack of available standards, only carnosic acid could be quantified. The antioxidant activity of the extracts was determined by the 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) test and the β-carotene bleaching test was used to study the differences in behavior of antioxidants in an emulsified medium for some of the extracts obtained. The results of the correlation studies to examine the relationship between the antioxidant activity (EC50), obtained by using the DPPH test, and the concentration of all the compounds detected in the extracts showed that carnosic acid was the more correlated compound, with a coefficient of correlation of −0.87. Using forward stepwise multiple linear regression, carnosic acid, methyl carnosate and carnosol were the compounds selected to predict the mentioned activity, with a value of 0.95 for the coefficient of determination.