Effect of beta-lactoglobulin and precipitation of calcium phosphate on the thermal coagulation of milk.
The effect of beta-lactoglobulin and heat-induced precipitation of calcium phosphate on the pH dependence and mechanism of thermal coagulation of milk throughout the pH range 6.3-7.3 was studied using serum protein-free milk and sodium caseinate as models for micellar and non-micellar milk protein systems respectively. It appears that the specific effect of beta-lactoglobulin at the pH of maximum stability may be related to its ability to chelate calcium. The effect of beta-lactoglobulin at the pH of minimum stability does not appear to be directly related to heat-induced dissociation of K-casein or micellar integrity but may be due to its ability to sensitize casein micelles to heat-induced precipitation of calcium phosphate, by increasing micellar hydrophobicity. The extent of heat-induced precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the pH dependence of heat stability. Micellar integrity appears to play a critical role in the heat stability of milk but for reasons not previously appreciated.
O'Connell
J E
JE
Department of Food Chemistry, University College, Cork, Irish Republic. connell@nizo.nl
Fox
P F
PF
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002130:Calcium Phosphates / Q000737:chemistry*; D002364:Caseins / Q000494:pharmacology*; D002417:Cattle; D002614:Chelating Agents / Q000494:pharmacology*; D011232:Chemical Precipitation; D005260:Female; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry / Q000494:pharmacology*; D008823:Micelles; D008892:Milk / Q000737:chemistry / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism; D012995:Solubility; D013499:Surface Properties
D002130:Calcium Phosphates; D002364:Caseins; D002614:Chelating Agents; D007782:Lactoglobulins; D008823:Micelles; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; D012964:Sodium; C485829:calcium phosphate, dibasic, anhydrous; D002118:Calcium