Does ultrafiltration have a lasting effect on the physico-chemical properties of the casein micelles?

The objective of this work was to determine if concentration of milk using ultrafiltration (in the absence of diafiltration) affects the physico-chemical properties of the casein micelles. The milk, once concentrated, was brought back to its original concentration and the physico-chemical properties as well as its susceptibility to rennet induced gelation were assessed. Although much is understood on the renneting behavior of concentrated milk, no information is available on how (or if) ultrafiltration per se modifies the properties of the micelles. Two times (2x) or five times (5x) concentrated milk (based on volume reduction) was prepared by ultrafiltration. Casein micelles were redispersed in their corresponding permeates and dialyzed against untreated skim milk. The stability of the casein micelles, their scattering properties, and the renneting properties were observed under the same volume fraction and ionic conditions of the skim milk control. There was a higher susceptibility to aggregation and a lower gel stiffness for the reconstituted micelles from the 5x milk compared to the 2x milk. 5x Ultrafiltration induced losses of calcium from the micelle, while 2x milk showed similar value as the control. The results suggest that the process of ultrafiltration affected the internal structure of the casein micelles, and this caused changes in the light-scattering properties and renneting functionality.