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Analytical studies of bovine milk
Abstract
The effects of traditional processing treatments on the amount and distribution of folates in bovine mild was investigated using high-performance liquid chromatography. The folates were extracted from samples by pH adjustment to 4.5 with acetic acid, and centrifugation to remove precipitated material. Conjugase treatment was employed to remove multiple polyglutamate residues. Folates were separated from other sample components using a reversed-phase column with a methanol-phosphate buffer (pH = 6.8), and ion-pairing with tetrabutylammonium phosphate. Quantitation of folates after separation from the milk matrix was accomplished by post-column pH adjustment to pH 2.5, and fluorescence detection. Milk was found to contain significant levels of 5-methyltetrahydrofolate. Both thermal processing and fermentation reduced the level of 5-methyltetrahydrofolate in milk. A high-resolution, two-dimensional electrophoretic technique was developed to separate the major proteins of milk. The first dimension was isoelectric focusing in the presence of a nonionic detergent and urea, using a modified pH gradient spanning pH 2.5 to 6.0. The second dimension consisted of electrophoresis in the presence of sodium dodecyl sulfate, in a polyacrylamide gel. This two-dimensional procedure was capable of resolving some whey proteins and the various classes of caseins. In addition, the technique could separate genetic variants within each class of proteins. The technique was used to study the effects of high speed centrifugation on the distribution of milk proteins, and to study degradation of milk proteins after proteolysis by a proteinase isolated from Pseudomonas fluorescens.
Subject Area
Food science
Recommended Citation
Holt, Douglas Lloyd, "Analytical studies of bovine milk" (1988). ETD collection for University of Nebraska-Lincoln. AAI8904490.
https://digitalcommons.unl.edu/dissertations/AAI8904490