No description available.

No description available.

No description available.

No description available.

published_or_final_version / Education / Doctoral / Doctor of Philosophy

by Peng Xiu Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 63-81). / Abstract also in Chinese. / Acknowledgment --- p.i / List of abbreviations --- p.v / List of Tables --- p.vii / Legend for figures --- p.x / Abstract (English) --- p.xi / (Chinese) --- p.xiv / Chapter PART ONE. --- INTRODUCTION AND METHODOLOGY --- p.1 / Chapter Chapter 1. --- Introduction and aim of study --- p.2 / Chapter Chapter 2. --- Biological background --- p.7 / Chapter Chapter 3. --- Literature reviews on serum fatty acids studies --- p.16 / Chapter Chapter 4. --- Subjects and methods --- p.25 / Chapter PART TWO. --- RESULTS AND DISCUSSION --- p.34 / Chapter Chapter 5. --- Omnivore adults --- p.35 / Chapter 5.1. --- Results --- p.37 / Chapter 5.1.1 --- Results on serum fatty acid composition in different groups --- p.37 / Chapter 5.1.2 --- Results on correlation of serum fatty acid composition with serum lipids and diet --- p.38 / Chapter 5.2. --- Discussion --- p.41 / Chapter Chapter 6. --- Omnivore children --- p.46 / Chapter 6.1. --- Results --- p.48 / Chapter 6.1.1 --- "Results on serum fatty acid composition, lipids and body fatness in the omnivore children" --- p.48 / Chapter 6.1.2 --- Results on correlation of serum fatty acids with blood lipids and body fatness --- p.49 / Chapter 6.2. --- Discussion --- p.50 / Chapter Chapter 7. --- Vegetarians --- p.52 / Chapter 7.1. --- Results --- p.53 / Chapter 7.1.1 --- Results on serum fatty acid composition in vegetarian adults and children --- p.54 / Chapter 7.1.2 --- Results on comparison of serum fatty acids in vegetarians to omnivores --- p.54 / Chapter 7.1.3 --- "Results on dietary intake, blood lipids and their correlation with serum lipids in vegetarian adults" --- p.53 / Chapter 7.2 --- Discussion --- p.57 / Chapter Chapter 8. --- Conclusion --- p.61 / References --- p.63 / Tables and figures --- p.81 / Appendix: Distribution of serum fatty acids analyzed by Gas-Liquid Chromatography --- p.118

 This study primarily aimed to evaluate the usefulness of fatty acids (FAs) in revealing trophic relationships in Hong Kong wetlands, through a combination of field studies and laboratory experiments. A field-based study in Mai Po mangroves involved FA profiling of basal food sources (i.e., leaf litter from three mangrove species, diatoms and macroalgae, and sediments) and consumers (particularly crabs). FA composition of all mangroves was similar, and lacked some polyunsaturated FAs present in diatoms and macroalgae. Uca and Sesarma crabs, with different feeding mechanisms, had divergent FA profiles: Uca arcuata FAs reflected a diet of macroalgae and diatoms, while FAs of Sesarma spp. were typical of mangrove leaves. Temporal changes in consumer FA profiles between 2001 and 2007 appeared attributable to increased sedimentation at Mai Po and shifts in organic content of the substratum. A second field-based study was conducted at Luk Keng marsh where a salinity gradient (0 to 30?) allowed investigation of the effects of salinity changes in FA profiles and stable isotope (carbon and nitrogen) signatures of the consumers and their foods. Basal food sources were leaf litter, including a fungal biomarker of decomposition (ergosterol), fine particulate organic matter (FPOM) and periphyton. Both FPOM and periphyton (but not leaf litter) contained 20:4 and 20:5 FAs, but their concentrations were affected by salinity. FA 20:4 occurred at higher levels in samples from fresh water, whilst FA 20:5 exhibited the opposite pattern and was more abundant under saline conditions, and thus the ratio of FA 20:4 to FA 20:5 decreased with increasing salinity. Combined application of FA biomarkers and isotopic signatures were able to elucidate trophic relationships between consumers and their food at Luk Keng confirming that FA 20:4 as a useful biomarker in the freshwater portion and FA 20:5 in the more saline area. FA 20:4 was particularly associated with predatory freshwater insects that had high δ15N values, but was scarce in primary consumers (snails, detritivorous beetles) with low δ15N values. Two laboratory experiments were undertaken to investigate: 1) the effect of diet on FA profiles in the apple snail, Pomacea canaliculata, and 2) interacting effects of diet and salinity on FA profiles of the Indian medaka fish, Oryzias melastigma. The results of the apple snail study showed that dietary-mediated changes in FA profiles were only reflected in the snail tissues after at least three months, and FA profiles of digestive tissues and neutral lipids were first to respond to the dietary change. The results of the medaka study demonstrated that the ratio of FA 20:4 to FA 20:5 was affected by both diet and salinity, reflecting a similar finding in the Luk Keng field study, although diet had a stronger effect on this ratio. The results of both field studies supported the use of FA profiles as food web tracers in wetlands and were complemented by laboratory results that yielded insights which will allow refinement of FA biomarker applications in food-web studies. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

The application of Nuclear Magnetic Resonance (NMR) spectroscopy in the determination of nutrition labeling component data (NLCD) was investigated, with the intent of using this methodology as a primary method to calibrate FTIR instrumentation for NLCD confirmation or screening on a routine basis. Unlike previous NMR studies, this work used three strategies to attain accuracy and reproducibility of NLCD through: (i) appropriate setting of operational parameters for spectral acquisition; (ii) resonance selection by optimizing the signal in proportion to the nuclei population and (iii) integration of resonances by pre-defined fixed chemical shift ranges. Both of 13C NMR spectra and 1H NMR spectra were shown to provide robust and acceptable results on the condition of appropriate acquisition of spectra for quantization purposes and the adoption of standard procedures for spectral processing, integration and calculation purposes. A quantitative approach of NLCD including trans content was determined by the interpretation resonance signals of 13C's and 1H's from methylene groups presented in triglyceride complex of fats and oils. An alternative method based on partial-least-squares (PLS) calibrations was provided as well, the latter proved to be especially useful in dealing with overlapping bands frequently found in 1H spectra. With the diagnostic provided by PLS, the trans and cis signals were shown to be separated in 1H spectra. It is the premise for the trans fat determination based on 1H spectra. Unit conversion from mole to weight % was addressed and a solution was developed based on NMR data per se, without significant assumptions. Validation involving the analysis of three different lipid types (model triacylglycerols, refined and hydrogenated oils) demonstrated that NMR predictions of NLCD were in good agreement with those results either from samples' actual values as well as those obtained using GC and FTIR predictions. Thus with appropriate integration of instrumentation, software and spectral processing accessories, both 13C and 1H NMR can determine NLCD, but with the capability to determine trans, 1H NMR is more practical than 13C NMR due to its much shorter spectral acquisition time. Thus NMR can serve as a primary method for the calibration of FTIR instrumentation, a practical instrumental method for routine NLCD determination and screening.

No description available.

Distinguishing animal fats from plant oils in archaeological residues is not straightforward. Characteristic plant sterols, such as beta-sitosterol, are often missing in archaeological samples and specific biomarkers do not exist for most plant fats. Identification is usually based on a range of characteristics such as fatty acid ratios, all of which indicate that a plant oil may be present, none of which uniquely distinguish plant oils from other fats. Degradation and dissolution during burial alter fatty acid ratios and remove short-chain fatty acids, resulting in degraded plant oils with similar fatty acid profiles to other degraded fats. Compound-specific stable isotope analysis of delta(13)C(18:0) and delta(13)C(16:0), carried out by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), has provided a means of distinguishing fish oils, dairy fats, ruminant and non-ruminant adipose fats, but plant oils are rarely included in these analyses. For modern plant oils where C(18:1) is abundant, delta(13)C(18:1) and delta(13)C(16:0) are usually measured. These results cannot be compared with archaeological data or data from other modern reference fats where delta(13)C(18:0) and delta(13)C(16:0) are measured, as C(18:0) and C(18:1) are formed by different processes resulting in different isotopic values. Eight samples of six modern plant oils were saponified, releasing sufficient C(18:0) to measure the isotopic values, which were plotted against delta(13)C(16:0). The isotopic values for these oils, with one exception, formed a tight cluster between ruminant and non-ruminant animal fats. This result complicates the interpretation of mixed fatty residues in geographical areas where both animal fats and plant oils were in use.