Interaction between β-casein and whey proteins as a function of pH and salt concentration.
The effectiveness of β-casein as a chaperone in the aggregation of whey proteins was investigated. β-Casein altered heat-induced aggregation as shown by a reduction in turbidity of β-lactoglobulin, α-lactalbumin, and bovine serum albumin (BSA) solutions. The pH of the mixtures greatly affected how much β-casein reduced the turbidity of the solutions; the maximum reductions in turbidity were observed at pH 6.0. Reducing the pH decreased the effectiveness of β-casein as a chaperone. An increase in ionic strength by the addition of NaCl or CaCl(2) also decreased the effectiveness of the chaperone. The addition of CaCl(2) had a larger effect than the addition of NaCl. The chaperone effect was seen at temperatures up to 145 °C. Differential scanning calorimetry (DSC) showed that β-casein did not alter the denaturation temperature of β-lactoglobulin. The kinetics curves for loss of native protein and turbidity development showed that β-casein did not function by slowing the aggregation process. It was concluded that β-casein competes with whey protein in the aggregate process and the aggregates formed in the presence of β-casein are smaller in size than those formed during whey protein self-aggregation. The formation of smaller aggregates gives rise to less turbid, more soluble protein solutions.
Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina 27695-7624, USA.
J J
JJ
Kehoe
E A
EA
Foegeding
D002122:Calcium Chloride / Q000494:pharmacology*; D002364:Caseins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008894:Milk Proteins / Q000737:chemistry*; D009994:Osmolar Concentration; D011485:Protein Binding / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology*; D000067816:Whey Proteins
D002364:Caseins; D008894:Milk Proteins; D000067816:Whey Proteins; D012965:Sodium Chloride; D002122:Calcium Chloride