Ruminant products, meat and milk, were long ago discovered to contain a high content of saturated fat associated with various chronic diseases in human, including coronary heart disease. Increased consumption of n-3 fatty acids, linolenic (LNA; 18:3n-3), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) by man has been linked with reduced incidences of these diseases. Therefore, in vitro experiments carried out in this thesis investigated the possibility that the dietary inclusion of essential oil compounds (EOC) might modify ruminal biohydrogenation of polyunsaturated fatty acids (PUFA), and thereby improve the fatty acid profiles of ruminant derived foods. In the first experiment, twenty EOC were screened, of which carvacrol, thymol, cis/trans-citral, geraniol, nerol, (+)-α-pinene, l-menthone, linalyl acetate and (R)-(+)-pulegone were most effective at protecting the PUFA from biohydrogenation. The reduced accumulation of stearic acid with concomitant increases in vaccenic acid following the addition of the EOC confirmed their capacity to inhibit biohydrogenation of both LA and LNA. However, the observed decreases in total volatile fatty acids concentrations suggested that the inclusion of these compounds at 300 mg l-1 also suppressed microbial fermentation. Of these EOC, carvacrol and thymol were the most potent inhibitors of fermentation as they decreased total VFA concentrations by ≥60% from those of the control. In the second experiment, selected EOC, namely linalyl acetate, l-menthone and (+)-α-pinene, were tested at lower doses. It was observed that these EOC when added at 100 and 200 mg l-1 also inhibited biohydrogenation with minimal effect on VFA concentration. In experiment 3, pure culture work was undertaken to assess the effects of EOC on three key Butyrivibrio spp., involved in the biohydrogenation process, namely B. fibrisolvens, B. hungatei and B. proteoclasticus. The EOC inhibited biohydrogenation through their bacteriostatic effects on these bacteria. In conclusion, these studies revealed that EOC have the potential to modify ruminal biohydrogenation to varying extents depending on the type of compound used and the dose applied. Consequently, they might be useful at improving the healthiness of ruminant products, however their effects have to be confirmed in vivo and ensure that they do not cause significant inhibition of fibre digestion.

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2006. / Summaries in English and Afrikaans. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (Ph. D.(Chemical Engineering)--University of Pretoria, 2000. / Summaries in English and Afrikaans. Adobe Acrobat Reader needed to open files.

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Thesis (Ph. D.)--University of Western Sydney, 2003. / A thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy, College of Science, Technology and Environment, University of Western Sydney, May, 2003. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 42-46). Also available on the World Wide Web.

Mémoire (M.Sc.)--Université du Québec à Chicoutimi, 1990. / Document électronique également accessible en format PDF. CaQCU

Thesis (PH. D.)--Columbia University, 1932. / Vita. eContent provider-neutral record in process. Description based on print version record. "Literature cited": p. 36-37.

Thesis (PH. D.)--Columbia University, 1932. / Vita. eContent provider-neutral record in process. Description based on print version record. "Literature cited": p. 36-37.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1915. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 52-60).