Analysis and evaluation of antioxidant flavonoids in buckwheat cultivars

The oxidation of low-density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Flavonoids are believed to reduce the risk of cardiovascular disease due to their antioxidant biological property. Quercetin and its glycoside rutin are naturally occurring flavonoids. Buckwheat is generally considered to be a major dietary source of rutin. The difference in the rutin content between species or varieties provides an opportunity to develop buckwheat lines with higher rutin content through hybridization. The objectives of this thesis were: (1) to explore antioxidant effectiveness of quercetin, rutin, alpha-tocopherol (vitamin E, a lipophilic antioxidant) and ascorbic acid (vitamin C, a hydrophilic antioxidant) in hydrophilic and lipophilic free radical generating systems; (2) to study the effect of quercetin on H2O2-induced oxidative stress in cardiomyocytes; (3) to develop a high performance liquid chromatographic assay for rutin in different buckwheat species and quantitatively analyze rutin in buckwheat seeds and leaves; (4) to investigate the protective effects of different buckwheat species or varieties against LDL oxidation and to determine the correlation between rutin content in buckwheat and the antioxidant activity of buckwheat.; The results of this study demonstrated that: (1) Quercetin and its glycoside rutin were more effective in inhibiting lipid oxidation in an aqueous environment surrounding plasma LDL than alpha-tocopherol or ascorbic acid; (2) Quercetin exhibited an in vitro inhibitory effect on the oxidative stress of neonatal cardiomyocytes; (3) A high-performance liquid chromatographic (HPLC) assay for rutin in different buckwheat species which was developed and validated in this project was accurate, rapid, and simple, and suitable for rutin analysis of different buckwheat species in routine application with good reliability and sensitivity. The species F. tataricum had the highest rutin content in its seed, followed by F. homotropicum , while F. esculentum, had the lowest rutin content in the seed. No correlation in rutin content was found between buckwheat leaves and buckwheat seeds; (4) The protective effect of the three buckwheat species against LDL oxidation was in the order: F. tataricum > F. homotropicum > F. esculentum. The antioxidant activity of the buckwheat cultivars was positively correlated to their rutin content.; The findings in this study demonstrated that quercetin and rutin had the potential to prevent the initiation of lipid oxidation, and that F. homotropicum could be used in buckwheat breeding programs. An improved buckwheat line, with high rutin content, has the potential to be used as a functional food for the prevention of cardiovascular diseases.