Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item SUPPLEMENTAL CHOLINE AND METHIONINE FOR DAIRY CATTLE: EFFECTS ON PERFORMANCE, LIVER FAT CONTENT AND GENE EXPRESSION, AND PLASMA AMINO ACID AND CHOLINE METABOLITE CONCENTRATIONS(2019) Potts, Sarah B; Erdman, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objectives of this dissertation were to 1) determine markers of post-ruminal choline supply so that bioavailability of rumen-protected choline (RPC) sources can be calculated in lactating cows and 2) investigate the production performance and metabolic effects of supplemental choline, methionine, or both on periparturient dairy cows. Observations from Experiment 1 indicated that of the 26 choline metabolites investigated, including 16 species of phosphatidylcholine (PC) and 4 species of lysophosphatidylcholine, free choline and betaine in blood and milk were most responsive to post-ruminal choline supplied via abomasal infusion. However, RPC did not elicit changes in blood or milk choline metabolites, even at the very high doses tested in Experiment 2. These results suggest that choline supplied as RPC is absorbed differently than choline supplied via abomasal infusion, that RPC is over-protected such that choline supplied in this form is not available to the cow, or that responses to RPC vary depending physiological state of the cow. Results from Experiment 2 indicated that primi- and multiparous cows respond differently to supplemental choline and methionine fed during the periparturient period. Feeding RPC to primiparous cows increased milk yield, while feeding rumen-protected methionine (RPM) had minimal effects on production. In contrast, RPM improved milk components and fat-corrected milk yield for multiparous cows. These observations suggest that primi- and multiparous cows have different methionine and choline requirements in the periparturient period. Investigation into the specific metabolic effects of choline and methionine fed to periparturient cows in Experiment 3 suggested that both RPC and RPM modify choline metabolism. The milk and blood PC profile was altered by both RPC and RPM. In line with this observation, RPC increased hepatic expression of the gene that encodes the enzyme responsible for catalyzing the rate-limiting step of PC synthesis via the CDP-choline pathway. The RPC-induced increase in hepatic betaine-homocysteine methyltransferase expression provided additional support for the connection between choline and methionine metabolism via one-carbon metabolism. Modification of postpartum plasma lactate concentrations by RPC for both primi- and multiparous cows, in conjunction with alterations in pre- or postpartum body condition, also suggest a choline-induced modification of tissue mobilization.Item Enhancing the availability of natural antioxidants in wheat-based food ingredients and food products through improved post-harvest treatments and processing conditions(2007-04-20) Moore, Jeffrey Calvin; Yu, Liangli; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wheat grain has significant antioxidant contents concentrated in the bran fraction, most of which may not be bioavailable in humans because they are not released from matrix materials during digestion. The present study developed solid-state enzymatic and yeast post-harvest treatments, and investigated the effects of these treatments and food processing on the extractable antioxidant properties of whole-wheat based food ingredients and food products. Antioxidant properties investigated in this study included scavenging capacities against cation ABTS radicals, peroxyl radicals (ORAC), hydroxyl radicals, and DPPH radicals, and total phenolic contents and phenolic acid compositions. The first part of this research developed and validated a high-throughput fluorometric hydroxyl radical scavenging capacity (HOSC) assay. The HOSC assay utilized a Fe(III)/H2O2 Fenton-like reaction to generate hydroxyl radicals, fluorescein as detector probe, trolox as an antioxidant standard, and area under the curve measurements to quantify scavenging capacity. The hydroxyl radical purity and potential solvent interference in the assay system were evaluated using electron spin resonance. The HOSC assay was found to have acceptable performance characteristics including linear range, accuracy, and reproducibility. The second part of this study investigated the potential of solid-state enzyme and yeast treatments to improve wheat bran antioxidant properties. Both enzyme and yeast treatments were capable of increasing available wheat bran antioxidant properties. Reaction parameters found to influence the effectiveness of these treatments to enhance wheat bran antioxidant properties included enzyme preparation and reaction moisture content for enzyme treatments, and yeast preparation along with dose and treatment time for yeast treatments. The final part of this research evaluated the effects of processing conditions including bran particle size, fermentation time, and baking conditions on the antioxidant properties of a whole-wheat pizza crust. Baking increased extractable antioxidant properties up to 82%. Fermentation time caused some significant increases, while bran particle size had no influence on extractable whole-wheat pizza crust antioxidant properties. This study suggests that post-harvest treatment of wheat bran and optimized processing conditions for whole-wheat food products are potential approaches for increasing their extractable antioxidant properties.