Evaluation by Sedimentation Field-Flow Fractionation of the Susceptibility of Nonfat Dry Milk Proteins to Aggregation

The proteins isolated from nonfat dry milk (NDM) which had been prepared with a high-temperature treatment (85°C for 30 min) were shown by sedimentation field-flow fractionation (SdFFF) to be highly susceptible to aggregation, with the formation of particles much larger than typical casein micelles (in addition to some micelles). The proteins of medium- and low-temperature NDMs, especially the latter, were less susceptible to such aggregation; caseins isolated from untreated milk do not aggregate under the same experimental conditions. The demonstration of such differences in susceptibility requires careful choice of SdFFF operation parameters, especially initial field strength and sample protein concentration, and the use of a second carrier to disperse or dissolve the aggregates and elute the redissolved protein from the separation chamber. Suitable operation parameters are provided.