Comparative study of rosemary extracts and several synthetic and natural food antioxidants. Relevance of carnosic acid/carnosol ratio.

The antiradical power, at equal concentrations of active principles, of the following antioxidants were studied using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay: butylated-hydroxyanisole, butylated-hydroxytoluene, tert-butylhydroquinone, ascorbyl palmitate, tocopherol, grape seed extract, olive extract and five rosemary extracts with different concentrations of carnosic acid (CA) and carnosol (COL). The reaction kinetics of DPPH scavenging activity in each studied substance identified significant variations in the time needed to reach the steady state. Rosemary extracts were seen to be more effective than the other compounds. CA had higher antioxidant activity than COL, although COL seemed to react faster with DPPH. The relevance of the CA/COL ratio for the antioxidant activity of rosemary extracts was also analysed. The presence of COL in rosemary extracts increased the antioxidant activity with an optimal CA/COL ratio of 2.5-3.0. Olive extract and grape seed extract seem to be very promising additives for use as technological antioxidants.