The objective of this research was to quantitatively describe the the denaturation and aggregation processes of a-lactalbumin at neutral pH in order to understand their interrelationship and effect on solution stability. Three different preparations of a-La had similar denaturation temperatures, enthalpies and % reversibility as measured by differential scanning calorimetry. However, Native PAGE reveled three non-native monomer bands that corresponded to three distinct dimer bands indicating specific intramolecular disulfide bond shuffling leads to formation of disulfide-specific dimers. The apo protein was the most thermostable to turbidity development. The Ca-La was the most thermostable holo- preparation. Turbidity development at 95 degreesC (95 degrees C) indicated pure preparations intensely associate through hydrophobic interactions through bridging by divalent phosphate and this effect was mitigated by decreasing the ionic strength, decreasing the phosphate charge to ¡V1 (at pH 6.6) or decreasing the temperature. The aggregation behavior of a commercial a-La was investigated at neutral pH and 95?aC in a complex mineral salt environment to understand general stability factors involved in a nutritional beverage. The objective was to understand the effect of a-La lot variation, relative b-lactoglobulin concentration and excess calcium on the aggregate size development as measured by light scattering and turbidity development. The lot of holo-a-La possessing a higher intrinsic b-Lg concentration had higher solubility at pH 6.80, evolved more reactive thiol groups, had a 25% faster first order rate constant, dissociated only slightly with cooling and formed spherical aggregates with a much higher molecular weight. Aggregates intrinsic to the protein powder may play a role in aggregate growth and shape. Adding increasing quantities of b-Lg generally decreased solubility. The highest b-Lg concentrations investigated demonstrated a net thiol oxidation and, subsequently, had a diminished ability to aggregate through hydrophobic interactions. Adding excess calcium caused a dramatic loss of solubility at pH 7.0 and required an increase in pH to 7.5 to regain solubility.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-05212004-155321 |
| Date | 04 August 2004 |
| Creators | McGuffey, Matthew Kenneth |
| Contributors | John van Zanten, E. Allen Foegeding, Tyre Lanier, Brian Farkas |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-05212004-155321/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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