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Food Structure

Abstract

Skim milk of approximately 3% total protein was ultrafiltered to 16.2% protein and 4.1 % lactose, and then diafiltered to reduce lactose to 2.1% and 0.9%. Total protein con ten t was maintained at approximately 17%. A ponion of the skim milk was condensed in a rising film evaporator to 14.7% protein and 15.7% lactose . All concentrates were spray dried at 120 to 125 °C inlet air temperature and 75 to 80 C outlet temperature using a rotary atomizer in a pilot plant spray dryer . Moisture content of the powders were 4.7 to 6.3% and lactose content ranged from 3.1% in diafilte red m i I k powder to 51 . 4% in the condensed mi I k powder. Scanning electron microscopy showed that powder partic les with the highest lactose content had a wrinkled surface and dents. Powder particles with lower lactose, including ultrafiltered and diafiltered milk powders, possessed dents but had no wrinkles and were smooth. When the lactose content of the diafiltered skim milk containing 0.9% lactose was raised to 15.6% by addition of lactose powder and then the product was spray dried, the powder particles showed a wrinkled surface. Intermediate lactose products, such as whey protein concentrate (37.1% lactose) possessed particles with a wrinkly surface as well. The wrinkles were not as pronounced as in powders with high lactose. Permeate powder containing 82.8% lactose had smooth particles with some wrinkles. Results suggest that lactose and protein influence the surface structure of milk powder particles.

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