Changes in casein composition of goats' milk during the course of lactation: physiological inferences and technological implications.
Five British Saanen goats were milk sampled during the first 39 weeks of lactation to determine changes in casein composition. Caseins were separated by anion- and cation-exchange FPLC to determine the relative amounts of the individual caseins. Acid, alkaline and SDS-PAGE were used to determine possible genetic polymorphisms and observe any lactational changes. Total casein nitrogen was determined using a micro-Kjeldahl method and this allowed the concentrations of individual caseins to be calculated. The milk of one animal, which had the deduced genotype alpha s1-CnAB, showed higher concentrations of both total and alpha s1-casein. The remainder of the group were either heterozygous alpha s1-CnBE or, more probably, homozygous alpha s1-CnE and produced milk of a generally lower protein concentration. Both FPLC and PAGE results showed that the relative amounts and concentrations of alpha s2-casein decreased with stage of lactation, consistent with its susceptibility to proteolysis. The relative amounts of the breakdown products of plasmin attack on beta-casein, gamma-caseins, were highly negatively correlated with milk yield (r = -0.942, P < 0.001) in the declining phase of lactation, reflecting the gradual involution of the gland at this time. The relative amount of kappa-casein increased by approximately 50% after peak lactation and its concentration almost doubled near the end of lactation. These compositional changes may alter the processing qualities of goats' milk in relation to cheese production.
Brown
J R
JR
Hannah Research Institute, Ayr, UK.
Law
A J
AJ
Knight
C H
CH
D000818:Animals; D000838:Anions; D002364:Caseins / Q000378:metabolism*; D002412:Cations; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006041:Goats / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000378:metabolism*; D009584:Nitrogen / Q000032:analysis; D013997:Time Factors
D000838:Anions; D002364:Caseins; D002412:Cations; D009584:Nitrogen