Effect of homogenisation on protein distribution and proteolysis during storage of indirectly heated UHT milk

This paper compares modifications in whey proteins and caseins and proteolysis during storage (120 days) at 20 degreesC of unhomogenised and homogenised milks (2% fat) heated (137 degreesC, 4 s) in a pilot-scale indirect UHT plant. Homogenisation resulted in the attachment of caseins and whey proteins to the milk fat globule membrane, changed the morphology of casein micelles and gave rise to small micellar particles, not easily sedimentable by centrifugation. It also promoted whey protein denaturation and slowed down enzymatic reactions that depend on residual proteinase, glycosidase and phosphatase activities. Homogenisation of milk before UHT treatment led to lower levels of the enzymes that contribute to deterioration during storage. This phenomenon, together with an increased complex formation between kappa-casein and beta-lactoglobulin, could be responsible for reduced proteolytic degradation.