Thesis (M. Sc.(Agric))(Horticulture)-University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Hops (Humulus lupulus L.) are primarily used to provide specific characteristics to beer, such as bitterness, aroma, flavor, and microbial stability. The chemical composition of hops, relative to how they are used during the brewing process, dictates the expression of these characteristics. Of the raw ingredients that go into making beer, hops are perhaps the most costly. Considerable resources are required to grow quality hops, and therefore, brewers and hop growers alike have a common goal of obtaining the highest quality hops possible. However, quality can be a relative term. While it is commonly agreed upon that high brewing values, such as α-acids and essential oil content, and robust structural integrity are indicators of quality hops, there are many opinions of the ideal aroma. Changes in the chemical composition of hops during plant maturation are a dynamic process requiring a comprehensive, in-depth chemical and sensory analysis in order to maximize the characteristics of interest to brewers. The complex aroma chemistry associated with hops in beer has been a confounding variable for the practical brewer, and a deeper understanding of hop aroma development during cultivation is needed. The effect of harvest date, location, and cultivar on key chemical components of Willamette and Cascade hops was investigated for the 2010 and 2011 growing seasons. Hops were harvested at 3 time points (Early, Typical, and Late), within a 3-week interval from 2 different farms in the Willamette Valley, Oregon. A split-plot experimental design for each cultivar was used; each farm represented a main plot and harvest years were designated as subplots. American Society of Brewing Chemist standard methods of analysis were used to measure moisture content, hop acids and their homologs, Hop Storage Index, total essential oil content and volatile profile by GC-FID. Additionally, difference testing, descriptive analysis, and consumer acceptance testing was conducted using beers brewed with either Typical or Late harvested Cascade hops from the 2010 harvest year. The response of analytes was dependent on the cultivar being examined, its location within the Willamette Valley, as well as days until harvest. Hop acids did not change appreciably during plant maturation for the period examined, while hop oil content increased hyperbolically to a plateau as the hops aged on the bine. Increases in oil quantity were strongly correlated (r > 0.90) with increases in α-pinene, β-pinene, myrcene, limonene, methyl heptanoate, and linalool concentrations. For Cascade, α-pinene, β-pinene, myrcene, limonene, ρ-cymene, caryophyllene, E, β-farnesene, and humulene all increased from Early to Typical points but no increase was observed between the Typical and Late time point. Linalool and methyl heptanoate increased between each time point while citral and humulene epoxide differed between Early harvest and Late harvest, but not between Early and Typical or Late and Typical harvests. For Willamette hops, α-pinene, β-pinene, myrcene, limonene, ρ-cymene, and linalool all increased between each time point. Caryophyllene, E β-farnesene, humulene, farnesol and citral all increased from Early harvest to Typical harvest but no difference was observed between Typical and Late. Clear sensory differences were found between beers brewed with Typical harvest Cascade hops and Late harvest Cascade hops, in terms of difference testing, descriptive analysis and consumer preference tests. / Graduation date: 2013

Thesis (D.Phil.(Horticultural Science)--University of Pretoria, 2009. / Includes summary. Includes bibliographical references.

M. Tech. Chemistry. / Discusses essential oils from indigenous Lippia species, L. scaberrima, L. rehmannii and L. javanica, can be used as bactericides and fungicides. Incorporation of these oils into a slow release gel will provide a mechanism for controlled prolonged release of the volatile compounds.

In the multi-step synthesis of Lilestralis, a synthetic muguet fragrance, the kinetics and mechanism of the formation of 3-(3-t-butylphenyl)-2-methylpropan-1-ol (m-LOL) and 4-(3-t-butylphenyl)-2-methylpropan-1-ol (p-LOL) from 2-methyl-3-phenylpropan-1-ol (MPP) and isobutylene using concentrated liquid phosphoric acid as a catalyst was investigated. By-products that include phosphate esters of MPP, m-LOL and p-LOL and oligomers of isobutylene were produced during this reaction and their role within the kinetics and mechanism was also investigated. When crystalline phosphoric acid is dissolved in water, it can form equilibrium polyphosphate mixtures at high acid concentrations. The phosphate species have the general formula Hn+2PnO3n+1 and consist of species such as orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7) and triphosphoric acid (H5P3010). The presence of polyphosphate within liquid phosphoric acid solutions used in this study was investigated using 31P NMR. To investigate the influence of water on the reaction, a number of experiments were performed using 1,4-dioxane as a solvent. This was chosen as the boiling points and density are similar to water, although it is classified as an aprotic solvent. Phosphate esters of MPP, m-LOL and p-LOL are produced as by-products and can potentially undergo hydrolysis when water is present, therefore reactions using aqueous phosphoric acid solutions may not give a true reflection of the concentration of phosphate esters produced. The use of heterogeneous catalysts was also investigated in order to improve yield and selectivity for p-LOL and m-LOL. These include acid catalysts such as solid phosphoric acid supported on Kieselguhr (SPA), sulphated zirconia and ultra stable zeolite-Y (H-USY).

Thesis (Ph.D.) -- University of Western Sydney, 2001. / "This thesis is presented in fulfilment of the degree of Doctor of Philosophy in Science at the University of Western Sydney, Richmond, New South Wales, Australia" Bibliography : p. 145-163.

Mémoire (M.Sc.B.)-- Université du Québec à Chicoutimi, 1988. / Egalement publie sur microfiche. Document électronique également accessible en format PDF. CaQCU CaQCU

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1995. / Document électronique également accessible en format PDF. CaQCU

Thesis (M.S.)--The University of North Carolina at Greensboro, 2009. / Directed by Gregory M. Raner; submitted to the Dept. of Chemistry and Biochemistry. Title from PDF t.p. (viewed May 17, 2010). Includes bibliographical references (p. 56-57).

No abstract available / Dissertation (MSc(Agric) (Agronomy))--University of Pretoria, 2007. / Plant Production and Soil Science / MSc(Agric) / unrestricted