Partitioning of Skim Milk Components as a Function of pH, Acidulant, and Temperature During Membrane Processing

¹ Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108

Skim milk was concentrated using a DDS-20 UF reverse osmosis module equipped with DDS HC-50 nanofiltration membranes. Temperatures were controlled over a range of 10 to 50°C. The pH of the milk was controlled with lactic acid and citric acid over a range of 5.6 to 6.8. Lower pH and lower temperatures improved component retention of the gross milk components, protein, lactose, and ash. Total solids, protein, and ash quantities in the retentates showed a significant pH effect on a wet basis and, in addition to lactose, on a dry basis. Protein, lactose, and ash quantities in the permeates showed a significant temperature effect on a wet basis, and ash showed a significant pH effect on both a wet basis and a dry basis. Fat was only detected in the retentates and at very low amounts only because skim milk was used. After concentration to approximately twofold by volume, permeated solids increased in all cases, and levels were higher at higher pH and temperatures. Ion partitioning as a function of temperature and pH was determined for samples by inductively coupled plasma analysis. Amounts of P, K, Ca, Mg, Al, and Zn showed a significant pH effect on both a wet basis and a dry basis. A significant temperature effect was shown for A1 and Na on a wet basis and for Al, Mn, Zn, Cu, Ni, and Cr on a dry basis.

Key Words: membrane processing • acidulant • temperature • pH

Submitted on May 20, 1991
Accepted on April 13, 1992