Subcritical water extraction of resveratrol from barks of Shorea Roxburghii G. Don.

Abstract

Phayom (Shorea roxburghii G. Don.) is a Thai plant traditionally known for its medicinal properties such as anti-cancer, anti-inflammation, cardiovascular disease and alzheimer disease protection. Phayom contains important polyphenolic compounds consisting of trans-resveratrol and glycosylated forms (known also as piceid), found especially in the barks. In general, the form existed in the plant is trans-piceid rather than free trans-resveratrol. Nevertheless, bioavailability of the trans-piceid is much lower, compared with that of the free trans-resveratrol. Therefore, this study aimed to extract trans-resveratrol and trans-piceid from Phayom barks obtained by subcritical water extraction (SCWE) and to obtain free form of trans-resveratrol via β-glucosidase hydrolysis of the extract. Firstly, the investigation was carried out to find suitable conditions for extraction of resveratrol from bark of Phayom with subcritical water. The effects of temperature (100-190 °C) and water flow rate (2-4 ml/min) were considered for extraction carried out for 6 hours, at a constant pressure of 10 MPa. The results were then compared with those obtained with conventional methods. The amount of trans-resveratrol in the extracts was found to be small (0.68 – 13.01 μg/g DW) compared with the amount of trans-piceid, whose maximum amount of 301.70 μg/g DW was obtained at 190 °C and at the flow rate of 3 ml/min. The amounts of trans-piceid obtained by the SCWE, solvent extraction and soxhlet extraction were 130.88, 68.37, 74.87 μg/g dry weight (DW), respectively. Overall, the extract obtained by SCWE has higher amount of trans-piceid than those of solvent extraction and soxhlet extraction. Secondly, the transformation of trans-piceid into free trans-resveratrol by using the enzymatic hydrolysis with β-glucosidase was studied. The hydrolysis was carried out at the incubation temperature of 30 °C and the incubation time of 17 hours. The results were compared for hydrolysis of various extracts obtained from SWE and other conventional methods. The amount of trans-piceid in the extracts obtained with soxhlet and reflux extraction with water was found to decrease as a result of β-glucosidase hydrolysis, while to the amount of trans-resveratrol increased. This result demonstrated that the conversion took place as a result of the enzymatic treatment of these water extracts. The hydrolysis of the subcritical water extract obtained at 190 °C gave similar results as that of the ethanol extract, that is, trans-piceid could not be converted to trans-resveratrol. Conversion of trans-piceid to trans-resveratrol may further be improved further by decreasing the extraction temperature and optimizing the hydrolysis condition.