It was attempted to produce pure fractions of the goat milk proteins αs1-casein, α-lactalbumin and β-lactoglobulin for use as internal standard in liquid chromatography. These three goat milk proteins have masses of 18191.27 Dalton, 14194.12 Dalton and 23615.33 Dalton respectively (UniProt, 2014), and are not similar to αs1-casein, α-lactalbumin and β-lactoglobulin from cow milk. Caseins are milk proteins which have an isoelectric point at 4.6 (McSweeney, 2003), and they do not have significant secondary and tertiary structures, which makes them very heat stable. This is due to their amino acid composition (Guelph, 2009). Whey proteins are the proteins left in the solution after precipitation (McSweeney, 2003).
The fractionation and purification was conducted with the use of preparative high-pressure liquid chromatography and freeze drying. The purity of the fractions was determined with time-of-flight liquid chromatography mass spectrometry.
All of the three previously mentioned goat milk proteins were attempted purified, but it was only proven possible to obtain 11 mg of ≥95% pure β-lactoglobulin from 38.12 ml skimmed goat milk, due to the time frame. This yield of 11 mg was only 10% of the maximum yield.
Furthermore a Bradford Protein Assay of the milk, and the purified protein, was made. This clarified that the Kjeldahl method and the Bradford Protein Assay does not provide the same values of protein concentrations for the same sample; the Kjeldahl method consequently gave higher concentrations of protein than the Bradford method did.