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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2019)
Chlorogenic acid (CGA) is a general term used to describe the most abundant group of phenolic acids in coffee. 3-CQA, 4-CQA, 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA are major CGAs in coffee; but only 5-CQA has been thoroughly studied. The first objective of this thesis was to study interactions between major CGA isomers and chemical changes in coffee brew that affect antioxidant activity noted for coffee. The second overall objective was to study the potential of these six major CGA isomers in modulating oxidative stress and inflammation using a human intestinal Caco-2 cell line. The findings from Chapter 2 suggested that the other five CGA isomers (4-CQA, 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) together account for more than 50% of the total CGA in coffee and contributed to the antioxidant activity of coffee brew. Chapter 3 and 4 addressed the research question of whether these major CGA isomers have a modulating effect on oxidative stress and inflammation in human intestinal Caco-2 cell line. Caco-2 cells were first incubated with, or without, individual CGA isomers, followed by a phorbol 12-myristate 13-acetate plus human interferon gamma challenge. Biomarkers of oxidative stress (intracellular ROS and GSH/GSSG) and inflammation (IL-8) were measured. The results demonstrated that CGA isomers scavenged intracellular ROS in inflamed Caco-2 cells, mitigated the drop in GSH/GSSG ratio and attenuated IL-8 secretion. Dicaffeoylquinic acids (3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) had a relatively stronger capacity to evoke protection compared to caffeoylquinic acids (3-CQA, 4-CQA, and 5-CQA). To elucidate the possible mechanism underlying these actions, the effects of CGA isomers on the nuclear factor kappa B signaling pathway, mitogen-activated protein kinase cascades, and nuclear factor (erythroid-derived 2)-like 2 signaling pathway were further investigated. In conclusion, structural differences in six CGA isomers were found to correspond to differences in antioxidant and anti-inflammation activities. CGA isomers attenuate oxidative stress and inflammation in Caco-2 cells by triggering changes in redox biology parameters, lead to an up-regulation of nuclear factor kappa B signaling at very early stage, mitigation of p38 phosphorylation and up-regulation of antioxidant genes in an intermediate stage, and activation of Nrf2 signaling at a much later stage.
The presence of Listeria spp. and L. monocytogenes (Lm) was investigated in provincially inspected food processing and retail facilities in British Columbia. Lm (n=56) was recovered in food processing environment (FPE) of dairy, meat and fish facilities, and in ready-to-eat fish products. The majority of Lm belonged to listeriosis causing serotypes 1/2a and 4b. Isolate fingerprinting revealed 14 sequence types, and 38 pulsotypes, with 66% of Lm possessing the full-length inlA, a causally linked virulence determinant. Unexpectedly, 4b serotypes more readily acquired point mutations leading to rifampicin resistance compared to other serotypes (p
No abstract available.
Maillard reaction products (MRPs) are produced when reducing sugars react with amino acids, peptides or proteins in heat-processed foods. The overall objective of this research was to isolate and identify MRPs that exhibit antioxidant and anti-inflammatory activities, from different sugar-amino acid model systems comprised of fructose, glucose or ribose, each with glycine (Fru-Gly, Glu-Gly and Rib-Gly) or lysine (Fru-Lys, Glu-Lys and Rib-Lys), respectively. The development of peroxyl radical scavenging activity was found to be positively correlated (r = 0.893-0.905, P
Master's Student Supervision (2010 - 2018)
Coffee contains biologically active components which may affect chronic disease risk.These biologically active components include caffeine, cafestol and kahweol, andantioxidants such as chlorogenic acids and Maillard reaction products (MRPs) that aregenerated during roasting. Although MRPs are regarded as being the most abundantgroup of antioxidants present in coffee, the mechanism underlying the antioxidant effectsof coffee MRPs in both in vitro and in biological systems has yet to be elucidated.In this study, the in vitro antioxidant properties of roasted and non-roasted coffee extracts(Coffea arabica L.) were tested using oxygen radical absorbance capacity (ORAC),Trolox equivalent antioxidant capacity (TEAC) and reducing power assays. MRPs wereshown to be the prevailing antioxidants in roasted coffee extracts. The mechanisms of theantioxidant action associated with coffee MRPs involve the hydrogen atom transfer (HAT)mechanism and the single electron transfer (SET) mechanism.The biological effects of MRPs derived from coffee extracts on the enzymatic antioxidantdefense in human colon adenocarcinoma Caco-2 cells were also investigated. Noinduction of antioxidant enzyme activities of catalase, glutathione peroxidase, glutathionereductase and superoxide dismutase were observed in Caco-2 cells after exposure tocoffee MRPs, except for an increased glutathione peroxidase activity after 24 h exposure.In contrast, significantly decreased activities of catalase and glutathione peroxidase, and areduced glutathione content were observed in Caco-2 cells after treatment with coffeeMRPs (p