Antioxidant potential of crocins and ethanol extracts of Gardenia jasminoides ELLIS and Crocus sativus L.: A relationship investigation between antioxidant activity and crocin contents

Crocins are water-soluble carotenoids responsible for the colour of saffron and gardenia. In this study, we isolated and identified three major crocins from gardenia, and then evaluated their antioxidant potential using four in vitro antioxidant tests in comparison with saffron ethanol extract (SE), gardenia ethanol extract (GE) and gardenia resin fraction (GRF). The relationship between total crocin contents and antioxidant activity of ethanol extracts of two herbs was investigated and the antioxidant potentials of three different polar crocins were compared. The crocins appeared to possess antioxidant activity when tested by four in vitro antioxidant models. However, in anti-hemolysis, DPPH radical-scavenging and lipid peroxidation assays, GRF exhibited significantly stronger antioxidant activity than crocins and no correlation between total crocin contents and antioxidative function was revealed, which implied that ingredients other than crocins in gardenia gave markedly strong antioxidant activity. In the phosphomolybdenum assay, antioxidant capacities of fractions and extracts correlated with total crocin contents (R = 0.93). Moreover, comparison of results indicated that sugars attached to the crocetin moiety seemed to be beneficial for the antioxidant activity of these water-soluble pigments.