Antioxidant activity of rosemary and sage extracts in rapeseed oil

Rosemary and sage leaves were extracted with hexane, acetone, ethyl acetate and ethanol. Yields of extracts and of carnosic acid contents were higher in solvents of medium polarity. Both carnosic acid and carnosol showed medium activity in deodorized rapeseed oil, about the same as that of butylated hydroxyanisole. Carnosic acid was moderately more active than carnosol and the resulting oxidative stability of extracts was correlated with the content of carnosic acid, but not with the content of carnosol. The antioxidant activity was about the same in rapeseed oil as in sunflower oil, but substantially lower than that in lard. Antioxidant activities, expressed as protection factors, were higher under Schaal oven test conditions at 40 or 60C than when determined in Oxipres at 100C. The dependence of the concentration of antioxidants and the protection factor showed similar negative exponential relations in all tests.