Distribution of proteins in concentrated skim milk reconstituted from low- and high-heat milk powders
1996
Ward, B.R. | Goddard, S.J. | Augustin, M.A. | McKinnon, I.R.
Heating, acidification and concentration and the order in which these processes are applied induce a number of changes to milk components. Heating of skim milk above 60 degrees C results in denaturation of whey proteins and association of denatured beta lactoglobulin with kappa-casein (Sawyer, 1969). Heating also causes changes in equilibria of milk salts (Pyne. 1962), dephosphorylation of casein (Belec & Jenness, 1962), cleavage of N-acetylneuraminic acid residues from kappa-casein and formation of dehydroalanine, lysinoalanine and Maillard reaction products (Walstra & Jenness, 1984). Acidification of milk is used in the manufacture of a number of dairy products such as yogurt, labneh and cottage cheese. Milks given a high preheat treatment gel at a higher pH (Heertje et al. 1985). It is known that acidification of milk causes dissolution of colloidal calcium phosphate and that this is sometimes accompanied by release of casein into the serum (Rose, 1968; Dalgleish & Law, 1988, 1989). Concentration of milk induces a decrease in pH with consequent effects on the partitioning of minerals. The aims of this work were (1) to compare the distribution of milk proteins between the serum and micellar phases of concentrated milks reconstituted from powders given a low or high preheat treatment and (2) to examine the effects of subsequent acidification of concentrated milk on this distribution. Information on the distribution of proteins will help in understanding the acid gelation of concentrated milk products.
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