摘要：Retentates containing 20, 27, and 34% total solids, obtained on commercial scale by the ultrafiltration of milk were spray-dried on laboratory scale using centrifugal atomization and single stage drying with the inlet air temperature of 220 C and the outlet air temperature of 90 C. The protein content in the powders was 31% to 35% compared to 24.8% protein in the control whole-milk powder. Lactose contents were markedly lower in the retentate powders (-10.6%) than in the milk powder (40.4%). Storage of the powders at 37 C resulted in a marked increase in the 5-hydroxmethylfural contents with doubling of this content in the retentate powders and tripling in the milk powder. When viewed by scanning electron microscopy, the spray-dried retentate powder particles had smooth surfaces free from wrinkles usually seen in spray-dried milk powders. When the same products were exposed to atmospheres having 75%, 85%, or 100% relative humidity, the retentate powders exhibited less lactose recrystallization than the milk powder. The melting temperature (Tm) (as determined by differential scanning calorimetry) of lactose present in the retentate powders was not affected by the reduced lactose content in the powders but the fusion enthalpy of lactose was reduced in the retentate powders compared to the control milk powder.
