The protective effect of Opuntia dillenii Haw fruit against low-density lipoprotein peroxidation and its active compounds

The antioxidant activity and inhibitory effect of extracts from Opuntia dillenii Haw fruit (ODHF) and its active compounds on low-density lipoprotein (LDL) peroxidation were investigated. The results indicated that the antioxidant activity of methanolic extracts of ODHF in Trolox equivalent antioxidant capacity and oxygen-radical absorbance capacity assays were in the order of seed > peel > pulp. The lag time of conjugated diene formation in Cu2+-induced LDL oxidation was increased by incubation of LDL with various methanolic extracts of ODHF. The methanolic extracts from seed, peel and pulp prolonged the lag time compared to control (154.1 min) to 514.8, 163.9 and 190.2 min, respectively, at a concentration of 10 μg/ml. Among the extracts, seed extracts of ODHF (10 μg/ml) possessed the highest inhibitory effect on the formation of thiobarbituric acid reactive substances and relative electrophoretic mobility. The results also demonstrated that seeds of ODHF contained the highest amounts of polyphenols and flavonoids (212.8 and 144.1 mg/100 g fresh seed, respectively), such as gallic acid, catechin, sinapinic acid, epicatechin, p-coumaric acid, quercetin and ferulic acid, but no betanin, isobetanin and ascorbic acid as determined by HPLC. However, the peel and pulp contained high amounts of betanin, isobetanin and ascorbic acid, but with lower contents of phenolics and flavonoids as compared to the seed. These findings suggest that phenolics and flavonoids may directly contribute to the antioxidant activity of the seeds of ODHF.