Protein Stability of Frozen Milk as Influenced by Storage Temperature and Ultrafiltration

Milk and milk concentrates containing 12–35% total solids were stored at 0, –2, –4, –6, –8, –12, and –20°C and protein stability of the thawed products was evaluated periodically. Samples stored at –4 to – 12°C exhibited poorer protein stability than samples stored at higher or lower temperatures. Ultrafiltered (UF) skimmilk with permeate: retentate ratios of 10:90, 20:80, and 30:70 were stored at –8°C and they remained stable at least three times longer than frozen control samples of UF skimmilk stored at the same temperature. When the extent of UF was increased to 40:60, protein stability in the frozen retentate declined somewhat as compared to that of less concentrated retentates.