Effect of loquat (Eriobotrya japonica) extracts on LDL oxidation

The antioxidative activity of the extracts of loquat fruits, Eriobotrya japonica Lindley was examined. Loquat fruit was separated into three parts (peel, flesh and seed), and each part was extracted with either water or ethanol. The extracts were then assessed for their free radical scavenging ability and effects on the oxidation of human low density lipoprotein (LDL) in vitro. Results in this study show that the ethanol extracts of all three loquat parts and the water extract of the peels exhibited a strong ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. Among extracts of different loquat parts, the ethanol extract of loquat seeds was the most potent one. The ethanol extract of the seed was also effective in suppressing the oxidation of linoleic acid which was demonstrated by a slow discoloration of β-carotene/linoleic acid conjugation system. The ethanol extract of loquat seeds as compared to other extracts could also suppress significantly the 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN)-induced LDL oxidation. When the content of total polyphenolic compounds in different loquat parts (peel, flesh and seed) was examined, a significantly higher level of total polyphenols was found in the seed than the peels and flesh. Using reverse-phase HPLC-ESI EM analysis, significant levels of polyphenolic compounds such as chlorogenic acid, cyanidine glucoside, epicatechin, epigalocatechin gallate and procyanidin B2 in the ethanol extract of different loquat parts were identified and quantified. The latter two compounds were found mainly in the ethanol extract of loquat seeds, but not in peels and flesh. Therefore, it is suggested that the high ability to scavenge free radicals and suppress the LDL oxidation exerted by the ethanol extract of loquat seeds was at least in part due to the high content of polyphenolic compounds in the seeds.