Heat and/or high-pressure treatment of skim milk: changes to the casein micelle size, whey proteins and the acid gelation properties of the milk

Skim milk was subjected to heat, pressure or combined processes. In general, higher levels of whey protein denaturation were observed for milk subjected to combined processes than those heat- or pressure-treated only. Heat treatment caused small changes to the casein micelle size. Pressure treatment decreased the casein micelle size; however, the effect was less marked when heat and pressure treatments were combined. Acidification of the skim milks produced gels with a range of firmness, yield stresses and yield strains depending on the treatments applied. These changes in acid gel properties were not related only to whey protein denaturation levels in the milks.     

Disruption of fat globules during concentration of whole milk in a pilot scale multiple-effect evaporator

The effects of heat treatment by direct steam injection (DSI) and concentration of whole milk using a pilot scale multiple-effect evaporator on fat globule size and the total milk fat globule membrane (MFGM) proteins were examined. In both nonpreheated and preheated whole milk, the size of milk fat globules decreased while the surface protein concentration of the fat globules increased as the milk passed through each effect of the evaporator. These results indicate that the fat globules were disrupted during DSI heating and evaporation and the proteins from the skim milk were adsorbed onto the fat globule surface.