abstract / Chinese Medicine / Doctoral / Doctor of Philosophy

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Graduation date: 1992

Thesis (Ph.D.) - University of St Andrews, April 2010.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 162-183). Also available on the World Wide Web.

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Chiang Yee-Ting. / Thesis submitted in: December 2002. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 116-130). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.ii / List of Abbreviations --- p.iv / List of Tables --- p.v / List of Figures --- p.vi / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- "Free radical, oxidative stress and antioxidants" --- p.2 / Chapter 1.1.1 --- Free radicals and reactive oxygen species (ROS) --- p.2 / Chapter 1.1.2 --- Oxidative stress and human diseases --- p.3 / Chapter 1.1.3 --- Dietary antioxidants --- p.5 / Chapter 1.1.4 --- Synthetic antioxidants --- p.5 / Chapter 1.2 --- Flavonoids ´ؤ polyphenolic compounds in plants --- p.8 / Chapter 1.2.1 --- Sources and biosynthesis of flavonoids --- p.8 / Chapter 1.2.2 --- Classification and dietary occurrence of flavonoids --- p.11 / Chapter 1.2.3 --- Functions of flavonoids in plants --- p.15 / Chapter 1.2.4 --- Effects of flavonoids in mammals --- p.16 / Chapter 1.2.5 --- Therapeutic application of flavonoids --- p.17 / Chapter 1.2.6 --- Absorption and metabolism of flavonoids --- p.26 / Chapter 1.3 --- Plant of interest --- p.28 / Chapter 1.4 --- Method used to characterize flaovnoid antioxidants in Vigna sinensis seeds --- p.30 / Chapter 1.5 --- Method used to evaluate the antioxidant activity --- p.31 / Chapter 1.5.1 --- p-carotene bleaching method --- p.31 / Chapter 1.5.2 --- "a,a-diphenyl- --- p.32 / Chapter 1.5.3 --- Single cell gel electrophoresis assay (Comet assay) --- p.32 / Chapter 1.6 --- Research objectives --- p.34 / Chapter 2 --- Materials and Methods --- p.35 / Chapter 2.1 --- Plant materials and chemicals --- p.35 / Chapter 2.2 --- Sample preparation --- p.36 / Chapter 2.2.1 --- Methanolic extraction method --- p.36 / Chapter 2.2.2 --- Acidic methanolic extraction method --- p.36 / Chapter 2.2.3 --- Optimization of extraction time --- p.37 / Chapter 2.3 --- Standards preparation --- p.37 / Chapter 2.4 --- Characterization of flavonoid antioxidants in V. sinensis seed extracts --- p.38 / Chapter 2.5 --- Evaluation of antioxidant activity --- p.39 / Chapter 2.6 --- Determination of free radical scavenging ability --- p.41 / Chapter 2.7 --- Evaluation of the protective effects on DNA damage --- p.42 / Chapter 2.7.1 --- Preparation of reagents --- p.42 / Chapter 2.7.2 --- Blood sample --- p.43 / Chapter 2.7.3 --- Hydrogen peroxide treatment --- p.43 / Chapter 2.7.3.1 --- Co-incubation system --- p.43 / Chapter 2.7.3.2 --- Pre-incubation system --- p.43 / Chapter 2.7.4 --- Establishment of optimal assay conditions --- p.44 / Chapter 2.7.4.1 --- Hydrogen peroxide concentration --- p.44 / Chapter 2.7.4.2 --- Sample volume --- p.44 / Chapter 2.7.4.3 --- Incubation time --- p.44 / Chapter 2.7.4.4 --- Hydrogen peroxide treatment time --- p.44 / Chapter 2.7.5 --- Ethidium bromide-acridine orange cell viability determination --- p.45 / Chapter 2.7.6 --- Slide preparation --- p.45 / Chapter 2.7.7 --- Comet assay --- p.45 / Chapter 2.7.8 --- Quantification of DNA damage --- p.47 / Chapter 2.7.9 --- Statistical analysis --- p.47 / Chapter 3 --- Results / Chapter 3.1 --- Comparison on the free radical scavenging abilities on two different V. sinensis seed extracts --- p.48 / Chapter 3.1.1 --- Optimal extraction time of methanolic extraction method --- p.48 / Chapter 3.1.2 --- Optimal extraction time of acidic methanolic extraction method --- p.48 / Chapter 3.1.3 --- pH values of two different V. sinensis seed extracts --- p.49 / Chapter 3.1.4 --- Free radical scavenging abilities of the two different V. sinensis seed extracts --- p.49 / Chapter 3.2 --- Determination of the stability of the V. sinensis seed extracts --- p.50 / Chapter 3.2.1 --- Effects of storage on the free radical scavenging ability of methanolic V. sinensis seed extract --- p.50 / Chapter 3.2.2 --- Effects of storage on the free radical scavenging ability of acidic V. sinensis seed extract --- p.50 / Chapter 3.2.3 --- Effect of storage on the antioxidant activity of methanolic V.sinensis seed extract --- p.51 / Chapter 3.2.4 --- Effect of storage on the antioxidant activity of acidic V. sinensis seed extract --- p.52 / Chapter 3.3 --- Identification of the flavonoid antioxidants in the acidic V. sinensis seed extract --- p.53 / Chapter 3.4 --- Evaluation of free radical scavenging abilitiesof identified flavonoids using the DPPH radical scavenging method --- p.54 / Chapter 3.5 --- Evaluation of antioxidant activities of the identified flavonoids using the β-carotene bleaching assay --- p.56 / Chapter 3.6 --- Evaluation of protective effects on DNA damage using the Comet assay --- p.57 / Chapter 3.6.1 --- Optimal comet assay conditions --- p.57 / Chapter 3.6.1.1 --- Hydrogen peroxide concentration --- p.57 / Chapter 3.6.1.2 --- Sample volume --- p.58 / Chapter 3.6.1.3 --- Incubation time with the seed extract in the co-incubation system --- p.58 / Chapter 3.6.1.4 --- Hydrogen peroxide treatment time --- p.58 / Chapter 3.6.1.5 --- Incubation time with the seed extract in the pre-incubation system --- p.59 / Chapter 3.6.2 --- Protective effects of the V. sinensis seed extracts and phenolic compounds --- p.59 / Chapter 3.6.2.1 --- Protective effects in pre-incubation system --- p.59 / Chapter 3.6.2.2 --- Protective effects in co-incubation system --- p.60 / Chapter 3.6.3 --- Protective effects of the identified flavonoids in acidic V.sinensis seed extracts and phenolic compounds --- p.60 / Chapter 3.6.3.1 --- Protective effects in pre-incubation system --- p.60 / Chapter 3.6.3.1.1 --- At 0.5 mM concentration --- p.60 / Chapter 3.6.3.1.2 --- At 1 mM concentration --- p.61 / Chapter 3.6.3.2 --- Protective effects in co-incubation system --- p.62 / Chapter 3.6.3.2.1 --- At 0.5 mM concentration --- p.62 / Chapter 3.6.3.2.2 --- At 1 mM concentration --- p.62 / Chapter 4 --- Discussion --- p.100 / Chapter 4.1 --- Comparison on the two different extraction methods --- p.100 / Chapter 4.1.1 --- Methanolic extraction and acidic methanolic extraction --- p.100 / Chapter 4.1.2 --- Free radical scavenging abilities on the two different V sinensis seed extracts --- p.100 / Chapter 4.2 --- Stabilities of two different V. sinensis seed extracts --- p.101 / Chapter 4.2.1 --- Change in antioxidant activity during storage --- p.101 / Chapter 4.2.2 --- Comparison on the stabilities of the extracts assayed under different conditions --- p.102 / Chapter 4.3 --- Identification of flavonoid antioxidants in the acidic methanolic V sinensis seed extract --- p.103 / Chapter 4.4 --- Antioxidant activities of the individual identified flavonoid antioxidants --- p.104 / Chapter 4.4.1 --- Antioxidant activities of the identified flavonoid antioxidants and the selected phenolic compounds in hydrophilic assay system --- p.106 / Chapter 4.4.2 --- Antioxidant activities of the identified flavonoid antioxidants and the selected phenolic compounds in lipophilic assay system --- p.107 / Chapter 4.5 --- Evaluation of protective effects on DNA damage using Comet assay --- p.109 / Chapter 4.5.1 --- Optimal conditions in Comet assay --- p.109 / Chapter 4.5.1.1 --- Effect of hydrogen peroxide concentration --- p.109 / Chapter 4.5.1.2 --- Effect of sample volume --- p.109 / Chapter 4.5.1.3 --- Effect of hydrogen treatment time --- p.110 / Chapter 4.5.1.4 --- Pre-incubation and co-incubation systems --- p.110 / Chapter 4.5.2 --- Protective effects of two different V. sinensis seed extracts and six phenolic compounds --- p.111 / Chapter 4.5.3 --- Protective effects of the identified flavonoids and the phenolic compounds --- p.112 / Chapter 4.6 --- Health beneficial properties of V. sinensis seeds --- p.113 / Chapter 5 --- Conclusion --- p.114 / References --- p.116

The Andean area of South America is the center of origin and diversity of the staple crop potato. Native Andean landraces represent a remarkable gene pool to exploit for the improvement of potato varieties. In the present study, the potential of the native germplasm was evaluated as a source of health-promoting compounds, and more particularly of dietary antioxidants. These phytochemicals receive an increasing interest due to their prospective effects on the prevention of various diseases such as cancers and cardiovascular diseases. In this study, a genetically diverse sample of 74 native potato cultivars (Solanum tuberosum L.) was field grown in 2004 in Huancayo (Peru, 3280 m above sea level). Using screening methods, we found a large variability of total phenolic, total carotenoid, and total vitamin C contents among the potato germplasm. The hydrophilic antioxidant capacity was also measured and was highly correlated with the total phenolics. On the basis of their contrasting contents, 23 potato cultivars were further selected for an in-depth analysis of their carotenoid, polyphenol, and tocopherol profiles. A wide range of antioxidant patterns could also be highlighted as well as cultivars of particular interest from a nutritional point of view. The stability of the ranking of cultivars across environment in terms of phenolic and carotenoid content was subsequently confirmed using 13 contrasted cultivars cultivated in 2005 in another highland environment (Huancani, Peru). This finding supports the fact that the potato genotype is the most determining factor of the observed variability. The effects of a drought stress on the dietary antioxidant contents were then investigated using a selection of five high antioxidant-contrasting cultivars. Drought-induced variations were complex with levels of antioxidants showing increase, decrease or remaining stable, depending on the genotype and the type of antioxidant considered. A gene expression analysis was finally used to gain an insight into the regulation of the production of the polyphenols. We demonstrated that the expression of 8 out of 13 polyphenol-related genes were coordinated and correlated with the polyphenol levels (both constitutive and drought-induced), supporting the fact that the production of polyphenols is, at least in part, controlled at the transcriptional level. Taken together, these results provide useful information concerning the health-promoting potential of the staple crop potato, and particularly of the native germplasm. We demonstrated the high diversity in potato tubers in terms of dietary antioxidants, identified genotypes with nutritionally interesting antioxidant composition, and highlighted their behavior under different environmental and drought stress conditions.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 158-184).

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Food Science." Includes bibliographical references (p. 103-117).