Antioxidant and binding properties of methanol extracts from indigo plant leaves

This study was conducted to clarify the effect of ultra-pressure treatment on the extraction of bioactive compounds from indigo plant leaves (Polygonum tinctorium Lour.) and on their properties. Leaves were harvested the in mid-August, 2013, from Naju City (Korea), and treated using two methods: ultra-pressure (550 MPa, 3 min) and hot-air (70°C, 24 h). Then, the leaves were ultrasonically extracted with methanol. The content of indirubin in leaves treated with ultra pressure and hot air was (535.55 ± 26.14) mg kg−1 and (52.63 ± 6.45) mg kg−1, respectively, and that of tryptanthrin was (165.55 ± 8.74) mg kg−1 and (153.00 ± 7.62) mg kg−1, respectively. Polyphenolic content in the leaves extract was (127.24 ± 13.67) mg kg−1 after the ultrapressure and (88.22 ± 5.33) mg kg−1 after the hot-air treatment. The content of flavonoids was (2298.67 ± 83.27) mg kg−1 after the ultra-pressure and (3224.00 ± 21.45) mg kg−1 after the hotair treatment. Di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH) radical scavenging activities of the indigo extract obtained by ultra-pressure and hot-air treatment methods at the concentration of 1 mg mL−1 were (80.25 ± 0.73) % and (66.54 ± 2.35) %, respectively, and 2,2′-azinobis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activities were estimated as (90.14 ± 0.79) % and (64.45 ± 8.97) %, respectively. The methanol leaf extract after ultra-pressure treatment exhibited higher binding properties to human serum albumin in comparison with catechin and conventional treatments. Consequently, it was assumed that the ultra-pressure treatment is an effective method for the extraction of bioactive compounds from indigo leaves.