Abstract:

Except that few sweet potato leaves are taken as edible food or livestock feed, most of them that contain large amounts of bioactive flavonoids are discarded, which leads to a great waste of available resource. In the present study total flavonoids were extracted from sweet potato leaves using ethanol and purified using macroporous adsorption resin. The extraction and purification procedures were optimized by orthogonal array design and one-factor-at-a-time methods, respectively. Additionally, antioxidant properties of the purified total flavonoids were evaluated by assaying their ·OH and DPPH· scavenging activities. The optimal extraction conditions were as follows: ethanol concentration 60%, material/liquid 1:40, and temperature 90 ℃ for a thermal refluxing extraction duration of 60 min, and 1 g of the crude extract obtained under such conditions contained 101.3 mg of total flavonoids. The optimal purification parameters using macroporous resin HPD 500 whose adsorption and desorption performance was superior to those of other resins including AB-8, NKA-9, HPD 600 and HPD 450 were as follows: sample concentration 1.8 mg/ml, pH 3, and sample flow rate 3 BV/h; taking 50% ethanol as eluent, eluent flux 3 BV/h, and eluent quantity 4 BV, and the content of total flavonoids in the purified extract was 488.7 mg/g. Both of the crude extract and the purified product displayed a good scavenging activity to ·OH and DPPH·

Key words: sweet potato leaves, flavonoids, HPD500 resin, extraction and purification, antioxidant activity