Study of Ultrasound-assisted Acid Hydrolysis to Obtain Quercetin and their Antioxidant Activities from some Plants
Authors: Hoang Le Huy , Phuong Pham Thi , Hanh Nguyen Thi , Do Ho Ba , Huy Nguyen Quang 
Published: December 2019

In this study, acidic hydrolysis to release the aglycone quercetin from plant extracts under ultrasound-assisted conditions was investigated. Based on the stability of quercetin, the suitable conditions were as follows: methanol/H2O (50:20, v/v) was added to the powder plants (ratio 50:1, ml/g), these mixtures were placed in ultrasonic bath of 37 kHz/550W; kept at 70°C within 30 min and then filtered. The filtrate was acidified with HCl (70:8, ml/ml). Lastly, the ultrasonication was carried out for hydrolysis for 1 hour (the second ultrasound) to obtain quercetin. We have obtained quercetin containing hydrolyzed extract from 10 plants to determine quercetin concentrations (using the HPLC optimized conditions) and evaluate the antioxidant activity (the capability to scavenge the DPPH radical). In 10 samples of plants that were obtained, both quercetin concentrations and antioxidant activity in the plant extract of the flower buds of Sophora japonica L have the highest value, then to the plant extract of Nelumbo nucifera Gaertn. In the Sophora flower-bud and the lotus leaf, quercetin content is calculated on dry material (mg/100g), 15423.04 and 5190.82  respectively; the average percentage inhibition of DPPH 100 µM (%) 55.26% and 32.23%., respectively.

Keywords: Quercetin, HPLC, acid hydrolysis, ultrasound-assisted, antioxidant activity.

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