Antioxidant activity and phenolic contents of extracts from the leaves of Acanthopanax trifoliatus harvested in different seasons

Acanthopanax trifoliatus or 'Phak Paem' is a deciduous shrub in Araliaceae which is commonly found in the north region of Thailand. This plant was traditionally used in Southeast Asia for ginseng-like purposes as a tonic to improve general weakness and for treatments of tuberculosis, lung hemorrhages and ulcers. Young leaves and the shoots are also popularly consumed as vegetables in northern Thai traditional cuisines. Leaf extracts of phak-paem were reported to promote some interesting biological effects including antioxidant, anti-inflammatory and anti-anxiety activities. This study aimed to evaluate the antioxidant properties of leaf extracts of A. trifoliatus collected from different seasons and quantitatively analyzed for both total phenolic and flavonoid contents. Eleven decoction extracts from the leaves of A. trifoliatus collected from different durations of a year were tested for free radical scavenging activity using DPPH scavenging assay and inhibition of lipid peroxidation of rat brain homogenate using TBARS method. Free radical scavenging activities of samples were evident while inhibitory effects to lipid peroxidation were evident too. Total phenolic and flavonoid contents of the extracts were determined using colorimetric methods. It was found that climatic condition such as temperature and rainfall had no effect to overall antioxidant activity of plant samples. However, samples collected in the winter especially in January and November were detected in high amount of total phenolic and flavonoid. This data suggests the optimum period for harvesting of plant raw material.