Determination and antioxidant analysis of seven flavonoids in bamboo-leaf extracts

Abstract

The flavonoid contents of different bamboo-leaf extracts and their relationships to antioxidant activity were investigated in this study by preparing nine samples using two commercially available bamboo-leaf extract products and seven bamboo-leaf extracts such as Phyllostachys edulis. A high performance liquid chromatography (HPLC) method was established to determine seven flavonoid components (orientin, isoorientin, vitexin, isovitexin, tricin, luteolin and luteoloside) in these samples, which were separated using a SymmetryShieldTM RP8 column (250 mm×4.6 mm, 5 μm) under gradient-elution conditions using acetonitrile as mobile phase A and 0.5% (v/v) acetic acid aqueous solution as mobile phase B. The antioxidant activities of the samples were evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical-scavenging assays, with half inhibitory concentration (IC50) as an indicator and the butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ) antioxidants as positive controls. Pearson correlation was then used to analyze the relationship between flavonoid content and antioxidant activity. The HPLC method was found to be accurate and reliable for determining the flavonoid contents of the bamboo-leaf extracts. The seven flavonoids were well separated, and good linear relationships were exhibited (correlation coefficients (R2)≥0.9990). Furthermore, the contents of the seven flavonoids in the bamboo-leaf extracts ranged from 14.97 to 183.94 mg/g, with the highest content of 183.94 mg/g recorded for Phyllostachys edulis. The bamboo species exhibited significantly different flavonoid contents, with Phyllostachys edulis showing the highest orientin, isoorientin, and vitexin levels of 38.45, 101.30, and 9.42 mg/g, respectively. Moreover, the bamboo-leaf extracts exhibited IC50 values of 78.23-179.41 mg/L for DPPH-radical-scavenging, while values of 203.48-1250.81 mg/L were recorded for hydroxyl radicals. The Phyllostachys edulis leaf extract exhibited the strongest antioxidant activity, with the lowest IC50 values of 78.23 and 203.48 mg/L for DPPH and hydroxyl, respectively; it showed greatly significant for the further development and application of Phyllostachys edulis. Finally, the relationships between flavonoid content and the DPPH- and hydroxyl-radical-scavenging activities (based on the IC50 values) were correlated, which revealed that the orientin and isoorientin contents are closely related to the antioxidant activities of the bamboo-leaf extracts. Consequently, the orientin and isoorientin contents can be used as indicators for evaluating the antioxidant activities of bamboo-leaf extracts.