Milk is a complex and complete food for the specific nutritional requirements of the
neonate. For the dairy industry, milk is a suitable raw material for the production of
other high value products. Although extensive research has been carried out on milk
of economically exploited dairy animals such as cow, goat, sheep, buffalo and camel,
there are properties which are not explicit in the milk of these, that are not completely
understood. Research of the milk from non-dairy animals, in which these properties
are explicit, may provide answers.
One of the unique properties is the content of oligosaccharides, which is low in the
dairy animals, but high in some species. This property points to a specialized
saccharide synthesis in the latter, where the whey protein α-lactalbumin may play a
role. Another unique property is the structure of casein micelles, which in the dairy
animals is stabilized by the presence of a specific ratio of four casein types, as well as
their specific structural properties. The most important is the κ-casein with its
amphipathic nature. In some non-dairy species, stable casein micelles are formed in
spite of the absence, or low content, of some of the casein types, specifically the κ-
casein.
The milk of the African elephant (Loxodonta africana) displays several unique
properties. In this research the proteome of its milk was investigated, with a focus on
α-lactalbumin and the caseins, in order to shed light on the mentioned unique
properties. The proteomics approach was used, which includes gel electrophoresis and
mass spectrometry. Computer modeling was also employed. The major proteins αs1-,
αs2-, β-casein, α-lactalbumin, β-lactoglobulin and serum albumin of African elephant
milk were identified with one-dimensional electrophoresis and mass spectrometry.
Better results were obtained with two-dimensional electrophoresis and orbitrap mass
spectrometry, with which α-lactalbumin, lactoferrin, β- and κ-casein were identified. The multiple sequence alignment of α-lactalbumins showed that there are six amino
acid positions that are unique to that of African elephant. Most of the amino acid
substitutions in this protein were found to be conserved, and the structure model of
African elephant α-lactalbumin was found to be homologous to the X-ray
crystallography structures of several species. Consequently the structure models of β-
1,4-galactosyltransferase 1 and the lactose synthase complex were built, again
showing homology to crystallographic data from other species. It may therefore be
concluded that structures of α-lactalbumin and β-1,4-galactosyltransferase 1 are
highly conserved amongst species. The saccharide synthesis in the African elephant
milk would probably not differ from that of other mammals, and may therefore not be
the reason for high levels of oligosaccharides in its milk.
The comparison of amino acid sequences and hydropathy plots of African elephant β-
casein with that of other species showed that it would self-aggregate and interact via
hydrophobic interactions with other caseins to form casein micelles, similar to the
model proposed for cowâs milk micelles. However, the African elephant β-casein
displays several more hydrophilic regions, compared to the cowâs protein.
The amino acid sequence and hydropathy plots predicted that African elephant κ-
casein would function in the same way as the equivalent of other species. The ratio of
African elephant milk κ-casein to β-casein was calculated to be approximately 1:8.5,
which is in the same order as camel and rat milk, compared to the 3:8 of cowâs milk.
This means that there would be very little κ-casein on the surface to effect repulsion
of the micelles. There should therefore be other protein regions protruding from the
micelle surface to aid in this function. It is suggested that in African elephant milk the
hydrophilic regions of β-casein carry out this role.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08202014-130037 |
| Date | 20 August 2014 |
| Creators | Madende, Moses |
| Contributors | Dr HE Patterton, Prof H-G Patterton, Prof G Osthoff |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-08202014-130037/restricted/ |
| 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 University Free State 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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