Theses and Dissertations

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    Cardiovascular-protective effects of blueberry consumption in postmenopausal women with above-normal blood pressure
    (Colorado State University. Libraries, 2023) Woolf, Emily K., author; Johnson, Sarah A., advisor; Gentile, Christopher L., committee member; Weir, Tiffany L., committee member; Rao, Sangeeta, committee member
    Endothelial dysfunction is the first step in atherosclerosis and contributes to its progression, and thus, is central to cardiovascular disease (CVD). It is driven by excessive oxidative stress and inflammation and characterized by impaired endothelium-dependent dilation. Estrogen-deficient postmenopausal women have oxidative stress-mediated suppression of endothelial function that is worsened by high blood pressure. Chronic blueberry consumption may be a beneficial dietary intervention for this population as it has shown to improve vascular function and blood pressure, though some studies have not demonstrated efficacy possibly due to the observed high interindividual variability in response to the intervention. Evidence indicates blueberries improve endothelial function, but studies have not been performed in postmenopausal women. Furthermore, ex vivo research has shown that blueberry (poly)phenols and their metabolites can decrease endothelial oxidative stress and inflammation, but whether these mechanisms translate to humans is unclear. The objectives of this dissertation were to 1) examine the efficacy of chronic blueberry consumption to improve endothelial function and blood pressure in estrogen-deficient postmenopausal women with above-normal blood pressure, with a specific focus on identifying mechanisms for improving endothelial function, 2) identify factors that contributed to the efficacy of blueberries as a dietary intervention for improving endothelial function, and 3) explore cellular mechanisms responsible for endothelial function improvements and the anti-atherogenic potential of blueberries. To investigate the aforementioned, we conducted a randomized, double-blind, placebo-controlled clinical trial and assessed endothelial function (measured through flow-mediated dilation (FMD)) and supine brachial blood pressure before and after daily consumption of 22 g of freeze-dried highbush blueberry powder or isocaloric placebo powder for 12 weeks. To examine mechanisms for improved endothelial function, FMD was assessed before and after infusing a supraphysiological dose of the antioxidant ascorbic acid (i.e. vitamin C) and normalized to shear rate area under the curve (FMD/SRAUC). To investigate factors impacting the interindividual variability in the endothelial function responses after the 12 weeks of blueberry consumption, we grouped the blueberry treatment group into responders (≥ +1% unit Δ FMD) and non-responders (< +1% unit Δ FMD) and performed secondary statistical analyses using data produced from the clinical trial. Lastly, to investigate mechanisms for improvements in endothelial function, we used a reverse translational human-to-cell approach leveraging human blood serum collected from participants in the clinical trial to perform ex vivo cell culture experiments. Results from the clinical trial showed that daily blueberry consumption significantly improved FMD/SRAUC compared to baseline by 96%. FMD not normalized for shear rate increased by 1.34% though the effects were not statistically significant (but were clinically significant). Improvements in FMD/SRAUC after blueberry consumption were due to reductions in oxidative stress as responses to ascorbic acid infusion were significantly reduced at 12 weeks in the blueberry group compared to baseline, with no changes in the placebo group. There were no major effects on blood pressure, arterial stiffness, endothelial cell protein expression, or other blood biomarkers of cardiovascular health. It was determined that the blueberry intervention was ~50% effective for improving FMD to clinically relevant levels of ≥ +1%, and that responders had decreased cardiovascular health and higher levels of circulating estrogen at baseline compared to non-responders. After 12 weeks of blueberry consumption, responders had reductions in oxidative stress, lower plasma nitrate levels, and higher phosphorylated endothelial nitric oxide synthase protein expression compared to non-responders. Lastly, we cultured HAECs with 15% serum (blueberry and placebo) for 1 h followed by 200 µM hydrogen peroxide (H2O2) for 24 h to induce endothelial dysfunction and evaluated the effects of blueberry (poly)phenol-rich serum on endothelial cell dysfunction and atherosclerosis progression. There were no statistically significant differences on monocyte binding, insulin-stimulated nitric oxide production, or peroxynitrite concentrations between dysfunctional HAECs treated with blueberry and placebo serum from the clinical trial. Collectively, results from these studies indicate that daily blueberry consumption for 12 weeks improves endothelial function in postmenopausal women with above-normal blood pressure through reductions in oxidative stress, and that efficacy (i.e. degree to which postmenopausal women responded to treatment in endothelial function) seems to be dependent on participant characteristics including cardiovascular risk factors and estradiol at baseline. Due to the inconclusive results regarding the ex vivo experiment, cellular mechanisms by which blueberry (poly)phenol metabolites impact endothelial function and atherosclerosis progression cannot be determined.
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    Open Access
    Medical student health behaviors and the influence on patient outcomes
    (Colorado State University. Libraries, 2011) Jortberg, Bonnie, author; Harris, Mary, advisor; Cunningham-Sabo, Leslie, advisor; Kennedy, Catherine, committee member; Johnson, Susan, committee member
    Purpose: Lifestyle habits are important risk factors for the development of cardiovascular disease, the leading cause of death in industrialized nations. The American Heart Association (AHA) and the National Cholesterol Education Program Adult Treatment Panel III (ATP III) recommend lifestyle changes as the primary and most cost-effective means of reducing the risk of coronary heart disease (CHD). Yet few physicians advise their patients about lifestyle modification. The main objective of this study was to determine if the nutrition and physical activity habits of medical students affect their patients' health behaviors on several important aspects of lifestyle modification: increased fruit, vegetable, and soy intake, and physical activity.
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    Open Access
    Microbial quality of mixed salad greens and selected fresh and dried herbs
    (Colorado State University. Libraries, 2010) Woo, Daniel Lee, author; Bunning, Marisa, advisor; Goodridge, Larry, committee member; Stone, Martha, committee member
    Direct marketing has been growing in the Western U.S., with 2007 sales of direct-marketed agricultural products totaling nearly $142.6 million in Colorado, New Mexico, Oregon, Idaho, Nevada and Washington-more than twice the 1997 sales level for the region. In addition, the number of farms engaging in direct sales to consumers grew by more than 20% to 18,274 in 2007. With increasing foodborne outbreaks linked to produce consumption, more research is needed to fill in the gaps of knowledge on the microbiological quality of leafy salad greens. Limited research has been conducted on the microbial safety and quality of farmers' market leafy salad greens. This study surveyed the microbial quality of salad greens from Larimer County farmers' markets in conjunction with salad mixes from a local supermarket. Leafy salad greens were obtained weekly for a period of four weeks from September to October, 2009, from both farmers' markets and supermarkets. Total aerobic and coliform counts were assessed within 48 hours of obtaining the samples via plating onto Petrifilm plates, then following one week of storage at refrigeration temperatures to observe changes in the microbial load. In addition, handling methods and temperatures were also recorded. Gloves and tongs were not used by vendors when handling salad greens. The vendors surveyed also lacked adequate refrigeration or ice for holding salad greens. Farmers' market salad greens were lower than supermarket salad greens in terms of initial aerobic plate counts. Both farmers' market and supermarket salad greens had no detectable levels of Escherichia coli and low levels of coliforms. After 1 week of storage, aerobic counts were higher in all samples (P<0.05). Coliform counts tended to decrease in all samples but no significant differences were observed (P>0.05). The results reiterate the need for consumers to thoroughly wash their salad greens. Further research should be conducted to assess the microbial quality o~ other produce at local farmers' markets. Herbs are often used in cooking to add aroma and flavor to foods. Consumers may choose to dry herbs from their garden or purchased from the market. Herbs, like other agricultural produce, may be exposed to a wide range of potential microbial contamination. There is currently little research on safe drying practices of herbs at home. Microwaving herbs is a potentially popular and time-saving approach for drying herbs at home. This research project investigated the impact of three drying methods (microwave, dehydrator, and conventional air drying) for improving the microbial quality of dried parsley and cilantro. Herb samples were obtained weekly from a local supermarket for a 2 month period from January to March, 2010. Standard guidelines from Oregon State University Extension service were followed for microwave drying of herbs. The manufacturer's drying temperatures/times were used for drying herbs in a dehydrator. Herbs were also air-dried for 1 week. Microbial testing was performed using plating onto 3M Petrifilm and when counts were below the detection limit, via the Most Probable Number (MPN) method. Microwave drying provided the greatest reduction in aerobic counts of bacteria in herbs. All drying methods reduced coliform counts to undetectable amounts; however, the determination of the effectiveness of each drying method in comparison with others for reducing the coliform count was complicated by the low initial load of coliforms in herbs used in the study.
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    Open Access
    Physicochemical modification of gliadin by black tea polyphenols: insight towards a nutraceutical therapy for celiac disease
    (Colorado State University. Libraries, 2022) Mathews, Paul, author; Van Buiten, Charlene, advisor; Gentile, Chris, committee member; Chung, Jean, committee member
    Celiac disease is an autoimmune disorder that affects approximately 1% of the global population. The pathogenesis of celiac disease is complex, involving the innate and adaptive immune responses. Exposure to gluten amongst genetically susceptible individuals initiates and propagates the disease process, with autoimmunity against endogenous tissue-transglutaminase enzymes manifesting intra- and extra-intestinal symptoms. Currently, the only mitigation strategy for celiac disease is an adherence to a gluten-free diet, which can be difficult to maintain. Recent advances in synthetic and natural products chemistry may offer therapeutic alternatives to the total abstinence from gluten containing products. The overarching objective of our research is to develop a nutraceutical approach to treating celiac disease using dietary polyphenols from tea. Within this thesis, we used a multi-spectroscopic approach to show that black tea polyphenols, which are rich in theaflavins and other flavanols, interact with gluten proteins in vitro to form colloidal complexes that result in structural change to the protein. These changes have the potential to reduce the immunogenicity of gluten via interference with digestion, sequestration, and conformational changes which may reduce recognition of the protein by immune cells. The interactions investigated here offer promise as a nutraceutical, plant-based therapy to acute gluten exposure in susceptible individuals.
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    Open Access
    Characterization of protein-polyphenol interactions between novel plant proteins (pea and hemp) and blueberry polyphenols with respect to polyphenol binding and delivery
    (Colorado State University. Libraries, 2022) Chima, Bianca, author; Van Buiten, Charlene, advisor; Johnson, Sarah, committee member; Prenni, Jessica, committee member
    Despite the numerous health benefits associated with polyphenols, dietary intake of this class of compounds is low in the United States due to low intake of fruits and vegetables. It has been shown that dairy foods (i.e. milk, yogurt) increase polyphenol bioavailability due to polyphenols interacting with whey protein, enhancing polyphenol stability and uptake throughout digestion. However, increasing concerns for sustainability and health have introduced a variety of novel plant-based proteins as dairy alternatives. This study aimed to investigate the abilities of edible pea and hemp protein isolates to form complexes with blueberry polyphenol extract (BPE) and characterize the physical and biological functionalities of these complexes compared to whey proteins. Protein/polyphenol solutions were analyzed using UV-Vis spectroscopy to determine if complexation occurred. Secondary structures and binding affinities were analyzed by far-UV CD Spectroscopy and fluorimetry, respectively. In vitro digestion was performed to determine whether the protein profile changed in the presence of BPE via SDS-PAGE and determination of free amino acids using the ninhydrin method. Protein isolates from pea and hemp successfully formed complexes with BPE with binding affinities for the compound similar to whey protein. Relative helicity of the hemp protein was higher than the other protein sources and increased upon complexation with BPE. Furthermore, the SDS-PAGE profiles of all the proteins were the same whether BPE was present or not and the free amino acid content increased after digestion for the protein and protein/polyphenol solutions. Overall, complexation of BPE with plant proteins was successful. Fluorescence quenching and changes to the secondary structure of the proteins in the presence of BPE indicate that polyphenols were bound but the mechanisms and structures responsible for complexation seem to vary between proteins. More research is needed to determine the interactions that cause binding between the polyphenols and the proteins and whether the bioavailability of the compounds will increase when bound to the proteins in cell model and/or clinical study. This study provides a foundation for exploring the effects of plant-based proteins on phytochemical functionality in complex, "whole food" matrices.