Seasonal variations of oxygen radical scavenging ability in rosemary leaf extract.

This investigation demonstrates that the oxygen radical scavenging ability of rosemary leaf extract has significant seasonal variations. The scavenging ability of rosemary leaf extract was quantitatively evaluated for five active oxygen species by using the ESR spin-trapping method. It was found that leaves that were picked in the cold season showed higher scavenging ability than those picked in the warm season. Measurement of the scavenging rate in pure rosmarinic acid and caffeic acid indicated that the scavenging ability in the warm season was mainly derived from rosmarinic acid. In the boiled extract, rosmarinic acid decomposed into caffeic acid. Therefore, a marked increase in the scavenging ability against superoxide and singlet oxygen in the boiled extract is in line with the high activity of caffeic acid. This study demonstrates that the multiple free radical scavenging method can be a useful method in comparative antioxidant capacity studies of plant extracts.