Online extraction-HPLC-FRAP system for direct identification of antioxidants from solid Du-zhong brick tea

Du-zhong brick tea (DBT), a new post-fermented functional tea, is marketed in China for its prevention of diseases from oxidative stress. However, antioxidant compounds in DBT are not clear. Here, a novel online extraction-HPLC-ferric reducing antioxidant power (OLE-HPLC-FRAP) has been developed to screen antioxidants in DBT. For OLE, guard column is packed with DBT (1.0 mg), then compounds are extracted directly by HPLC mobile phase for HPLC-FRAP analysis without sample pretreatment procedures. Eleven antioxidants have been screened and identified, three of which are detected in Du-zhong for the first time. Contributions of eleven antioxidant compounds to total antioxidant activity are evaluated using chlorogenic acid as antioxidant marker. Results indicate that the developed OLE-HPLC-FRAP system is a simple and powerful tool to analyze antioxidant compounds from solid complex mixtures, which also contribute to the enhancement of the value of DBT as a good functional tea.