Transforming naringin using the mycelium of Trichoderma harzianum CGMCC 1523 produces two metabolites, 3',4',5,7-tetrahydroxy flavanone-7-rhamnoglucoside (3'-OHN) and 3',4',5',5,7-pentahydroxy flavanone-7-rhamnoglucoside (3',5'-DOHN), both of which were characterized by ESI-MS, H-1 NMR and C-13 NMR analyses. The time course of the biotransformation by T harzianum showed that 3'-OHN and 3',5'-DOHN appeared simultaneously at 6 h, and the conversion yield (32.6%) of 3',5'-DOHN was higher (10.6%) than that of 3'-OHN at 56 h. The optimal biotransformation temperature was 30 degrees C, the optimal pH was 5.0, and the optimal concentration of naringin was 400 mg/l. The bigger volume of biotransformation mixture and lower shaking speed did not favor hydroxylation reactions. The radical scavenging activity of naringin at 2000 mu M was 11.1%, whereas activity of 3'-OHN at 100 mu M could reach 38.4%, which is 68.6 times more than naringin. Antioxidative activity of 3',5'-DOHN was increased 13.5% at 100 mu M compared to 3'-OHN. (C) 2009 Elsevier Inc. All rights reserved.