572. The heat coagulation of milk

Abstract

1. A study of the compositional factors which affect the heat coagulation of milk has been undertaken.2. Calcium-ion concentration and colloidal phosphate content appear to be the chief factors determining the tendency of a milk to coagulate on heating.3. Acidity (mainly derived from thermal decomposition of lactose and casein) and heat denaturation of casein are supplementary coagulation factors which develop during the heating process.4. Lactose, as the main source of heat-developed acidity, is an important secondary factor in heat coagulation, but not an essential one. Coagulation can proceed, though more slowly, in its absence. The serum proteins play no part in the phenomenon.5. A provisional theory of the heat coagulation of milk based on these findings is put forward.

Heat Stability and Salt Balance of Buffalo Milk as Affected by Concentration and Addition of Casein

“…He found that the heat stability of milks relate predominantly to differences in the composition of their serum conponents. The "effective calcium ion concentration" was held to bear an inverse relationship to heat stability (Pyne and McHenry 1955). Further, when milk is concentrated there is a shift of minerals from the dissolved to the colloidal phase which causes a decrease in the net negative charge on the casein micelles.…”

Heat‐induced coagulation of whole milk by high levels of calcium chloride

“…Because a reduction in pH to the isoelectric point causes precipitation of milk proteins, it is not surprising that in heat stability studies of calcium‐added milks, it is often concluded that heat coagulation results from a concomitant pH drop in milk. However, some studies also suggest that heat stability may be largely determined by the free calcium ion concentration, and the influence of acidity may be a secondary factor in the heat coagulation of calcium‐supplemented milk (Pyne and McHenry 1955; Morrissey 1969; Jeurnink and de Kruif 1995).…”

Milk Coagulation and Protein Denaturation

“…According to Fox (1981A,B), when milk is heated at elevated temperatures for prolonged periods of time, additional acidity develops as a result of (1) the production of organic acids, principally formic, from lactic acid, (2) the release of hydrogen ions by precipitation of primary and secondary calcium phosphate, and (3) the release of hydrogen ions by hydrolysis of casein phosphate and its subsequent precipitation as Ca3(P04b. These reactions contribute 50,20 and 30%, respectively, to pH decline (Pyne and McHenry 1955).…”

“…For example, a-lactalbumin is more susceptible to denaturation in milk than in whey, but the opposite is true of ,B-Iactoglobulin (Elfagam and Wheelock 1977). Many factors influence milk stability in these complex systems (Holt et al 1978;Pyne and McHenry 1955;Rose 1961A,B, 1963Sweetsur and White 1974;Tessier and Rose 1964) during heat treatments, ranging from 72°C for 15 sec for pasteurization to 120°C for 20 min or 142°C for several seconds for sterilization (Creamer and Matheson 1980;Douglas et al 1981). Casein is most important in determining the properties of milk products because of its high concentration (Payens 1978), but ,B-Iactoglobulin has a larger effect on a molar basis (de Wit 1981;Fox and Morrissey 1977;Rose 1961A,B, 1963.…”

“…Early studies were prompted by the need to ensure sufficient heat stability for evaporated milk to withstand heat sterilization Hart 1919, 1922). Between 1919 and1960, most attention was directed to the influence of milk salts on heat stability (Miller and Sommer 1940;Pyne 1958;Pyne and McHenry 1955). It was not until the early 1960s that the importance of heating time and pH on coagulation of milk was appreciated (Rose 1961A,B).…”