Heat stability of homogenized milk: role of interfacial protein

Abstract

The role of interfacial protein in determining the heat stability of recombined milk was investigated by removing serum protein prior to homogenization and reincorporating it after homogenization. In addition, the surface protein composition of recombined fat globules was probed by analyses of protein load and by quantification of the individual surface protein components using FPLC. In the absence of serum protein, substantially more casein was bound to the fat surface during homogenization. Despite this, the detrimental effect of homogenization on heat stability did not occur when serum protein had been removed from the system. Reincorporation of serum protein after homogenization caused the heat coagulation time-pH profile to revert to a form very similar to that observed without removing serum protein from the system. Thus, adsorption of serum protein did not affect heat stability. It is more likely that heat-induced interactions of serum protein with surface-adsorbed casein promoted heat coagulation. Fat surface area rather than casein load affected these interfacial protein-protein interactions during heating.

Composition and Structure of Fat Globule Surface Layers in Recombined Milk

“…The ratio of casein/whey protein in the cream layer (8.83) was higher than that in recombined milk (3.83), indicating a preference for adsorption of casein. This confirmed earlier observations on fresh homogenized cream and milk (Darling and Butcher, 1978;McPherson et al, 1984) and recombined milk (Oortwijn and Walstra, 1979;McCrae et al, 1994). Furthermore, Sharma and Dalgleish (1993) found no whey proteins at the fat globule surfaces in fresh homogenized milk.…”

Homogenization of milk emulsions:use of microfluidizer

“…The concentration of casein and serum protein at the fatherum interface of recombined milk was determined by the method described by McCrae et a1 (1994). A simulation process was carried out using Minitab vs. 8 to obtain a measure of the precision in which the concentrations were determined (McCrae et al, 1994).…”

“…During this process fat globules are disrupted to a considerable degree. As a result, a larger fat surface area is created which is stabilized by the adsorption of skim milk protein, mainly casein (Jackson and Brunner, 1960;Oortwijn and Walstra, 1979;Walstra and Oortwijn, 1982;McCrae et al, 1994). When there is insufficient material available to coat the fat globule surface properly during homogenization fat globules share skim milk protein, thereby forming clusters of fat (Ogden et al, 1976;Oortwijn and Walstra, 1979).…”

Heat stability of concentrated skim milk as a function of heating time and temperature on a laboratory scale – Improved methodology and kinetic relationship

“…Despite this, major influencing factors on heat stability of concentrated and unconcentrated milk could be unravelled. Especially pHdependency of HCT as well as the effects of different mineral composition of the serum phase, whey protein denaturation and technological pre-treatments such as various preheat treatments of the milk used and the effect homogenisation were investigated (McCrae, Hirst, Law, & Muir, 1994;Newstead, Conaghan, & Baldwin, 1979;Sweetsur & Muir, 1982;Tan-Kintia & Fox, 1999;Whiteley & Muir, 1996). Nevertheless, the reaction kinetics eventually leading to the formation of large particles should be further addressed.…”