Hawthorn fruit extract has been shown to have many health benefits including being cardiovascular protective, hypotensive and hypocholesterolemic. The present study was carried out to characterize further the antioxidants of hawthorn fruit and their effect on the oxidation of human low density lipoprotein (LDL) and α-tocopherol. The dry hawthorn fruit was extracted successively with ether, ethyl acetate, butanol and water. The ethyl acetate fraction was only effective in inhibition of Cu+2-mediated LDL oxidation. The column chromatographic separation led to isolation of eight pure compounds; namely, ursolic acid, hyperoside, isoquercitrin, epicatechin, chlorogenic acid, quercetin, rutin and protocatechuic acid. All of these phenolic compounds, except ursolic acid, were protective to human LDL from Cu+2-mediated LDL oxidation. They were also effective in preventing the peroxy free radical-induced oxidation of α-tocopherol in human LDL. The inhibitory effect of these compounds on oxidation of LDL and α-tocopherol was dose-dependent at concentrations ranging from 5 to 40µM. In addition, supplementation of 2% hawthorn fruit powder significantly elevated serum α-tocopherol by 18-20% in rats fed a 30% polyunsaturated canola oil diet, as compared with the control. The present results suggest that part of the mechanism for cardiovascular protective effects of hawthorn fruit might also involve the direct protection to human LDL from oxidation or indirect protection via maintaining the concentration of α-tocopherol in human LDL.

Green tea catechins (GTCs) as a mixture of (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallocatechin gallate (EGCG) possess a variety of biological activities. We have previously studied the stability of GTCs either as a mixture or as individual epicatechin derivatives in various pH, demonstrating that GTCs as a mixture in alkaline solutions were extremely unstable and degraded almost completely in a few minutes, whereas in acidic solutions (pH<4) they were very stable. For the pH ranging from 4 to 7, the stability of GTCs was inversely associated with the pH value of the incubation solutions. The present study examined the effect of ascorbic acid and citric acid on the stability of GTCs incubated in sodium phosphate buffer (pH =7.42). Ascorbic acid added to the incubation mixture significantly increased the stability of GTCs whereas citric acid exhibited no effect. Four epicatechin derivatives examined demonstrated varying stability, with EGCG and EGC being equally instable and EC and ECG being relatively stable. The addition of ascorbic acid significantly increased the stability of all four derivatives, particularly EGC and EGCG. The present results, although not directly transferable to in vivo conditions, may suggest that the presence of ascorbic acid may stabilize the GTCs in the intestine where the pH is neutral or alkaline before absorption.