Flow field-flow fractionation in the study of dairy products

Abstract

The performance of flow field-flow fractionation (FlFFF) was studied in the particle size analysis of dairy products including whey proteins, casein micelles, and fat globules, over a wide size range. The products investigated were full-fat milk, skim milk, cream, ice cream, powdered milk, nonlactose milk, and infant formula. In addition, three bacteria (Pediococcus acidilactici streptococcus, Propionibacterium, and Lactococcus lactic micrococcus) related to dairy processing were examined. FlFFF results were found to be consistent with literature values and data obtained by dynamic light scattering. A very-low-ionic-strength carrier had to be used to avoid complete adsorption of the casein micelles on the membrane inside the FlFFF channel. The observed particle size was also found to depend on the ionic strength and flow rate of the carrier. These dependencies were attributed to the electrostatic interaction between casein micelles and the channel wall and variations an the micelle size with ionic strength. Of the three membranes tested, regenerated cellulose and polyolefin materials produced similar particle size values, whereas the values obtained with polysulfone membrane were too high. When the pH of the carrier was raised in FlFFF, the casein peak shifted to a lower particle size, but when the pH was increased in light-scattering studies, a constant size was obtained. © 1997 John Wiley & Sons, Inc. J Micro Sep9: 601–609, 1997