Isolation of carotenoids, flavonoids and polysaccharides from Lycium barbarum L. and evaluation of antioxidant activity

A preparative column chromatography method was developed to isolate carotenoids, flavonoids and polysaccharides, from Lycium barbarum L., possessing vital biological activity, and their antioxidant activity was evaluated. Carotenoids were isolated by a column containing magnesium oxide and diatomaceous earth (1.5:1, w/w), and β-carotene was eluted with hexane, β-cryptoxanthin and neoxanthin with ethyl acetate and zeaxanthin with ethyl acetate–ethanol (80:20, v/v). Flavonoids and phenolic acids were separated using a Cosmosil 140 C18-OPN column, with phenolic acids being eluted with deionized water and neutral flavonoids with methanol. Polysaccharides were fractionated using a DEAE-Sepharose CL-6B column; neutral polysaccharides were eluted with water and acidic polysaccharides with different concentrations of NaCl. For antioxidant activity, the flavonoid fraction was the most effective in scavenging DPPH· and ABTS+ free radicals, chelating metal ions and reducing power, while the zeaxanthin fraction and polysaccharides showed the most pronounced effect in scavenging hydroxy free radicals and superoxide anions, respectively.