Modeling Flux of Skim Milk as a Function of pH, Acidulant, and Temperature

¹ Minnesota-South Dakota Foods Research Center, Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108

Skim milk was concentrated using a DDS-20 UFRO unit equipped with DDS HC-50 RO nanofiltration membranes. We studied the effect of the operational parameters of temperature, pH, acidulant, and applied transmembrane pressure on performance as evaluated by flux and component partitioning. Milk temperature, milk pH, percentage of total solids, inlet and outlet pressures, and temperatures were monitored and controlled throughout the experiments. Flux was recorded as a function of temperature, pH, acidulant, and applied pressure. Higher temperatures, pH, and pressures gave greater flux; and lower temperatures, pH, and pressures gave lower flux. Transmembrane pressure had the greatest effect, followed by temperature and then by pH. Equations were generated to model flux as a function of transmembrane pressure, temperature, and pH. There was no difference in effect caused by acidulant. Flux decline, Q₁₀, and activation energies were calculated. Arrhenius relationships were valid for skim milk under the experimental conditions.

Key Words: flux • skim milk • pH • acidulant • temperature

Submitted on May 20, 1991
Accepted on March 27, 1992