Food Chem 2011 Aug 27;127(3):1287-93. Epub 2011 Jan 27.
Department of Pharmaceutical Chemistry and Pharmacognosy, Faculty of Pharmaceutical Sciences and Center of Excellence for Innovation in Chemistry, Naresuan University, Phitsanulok 65000, Thailand. Electronic address:
Aqueous extract from Orthosiphon grandiflorus tea was on-line screened for its antioxidant components based on their capacity to scavenge free DPPH (1,1-diphenyl-2-picrylhydrazyl) radical after separation by a LC gradient. The structural elucidation of the active compounds was achieved by negative ionisation LC-ESI-MS/MS. Based on their mass spectra and fragmentation patterns related to antioxidant activity trace, seven compounds showing strong DPPH scavenging were identified to be danshensu, caffeic acid, caftaric acid, rosmarinic acid, caffeic acid derivative, sagerinic acid and salvianolic acid B. It is noted that danshensu, caftaric acid, sagerinic acid and salvianolic acid B have been reported in O. grandiflorus for the first time. In addition, the quantification of antioxidant compounds was performed using LC-MS/MS in multiple reaction monitoring (MRM) mode. Rosmarinic acid was found as a major component responsible for the antioxidant activity of this plant extract.