Influence of protein standardization by ultrafiltration on the viscosity, color, and sensory properties of 2 and 3.3% milks

Permeate and retentate (ca. two times concentration factor) from the ultrafiltration (UF) of skim milk were combined, and cream was added to produce milks with 2% and 3.3% fat and a range of true protein contents of 0.9, 1.8, 2.8, 3.7, and 4.6% within each fat level. A panel that had been trained for descriptive sensory analysis evaluated the appearance, aroma, flavor, and textural attributes of these milks. The relative viscosity and Hunter color values for whiteness (L value), greenness to redness (a value), and blueness to yellowness (b value) were determined. A decrease in the protein content of 2 and 3.3% fat milks by UF made them less white (lower L value), greener (lower a value), slightly less blue (slightly greater b value), and less viscous (lower relative viscosity). A change in protein content had less effect on whiteness (L value) and greenness (a value) of 3.3% fat milk than of 2% fat milk. Within the range of protein percentages studied, no changes in flavor or aroma descriptors were detected for either 3.3 or 2% fat milks. The protein content of 3.3% fat milk could be changed by UF within the range of 1.8 to 3.7% true protein with virtually no change in sensory properties. Protein content of 2% fat milk could be adjusted by UF between 2.8 to 1.8% true protein with no change in sensory scores. A further decrease to 0.9% true protein caused scores for appearance descriptors to decrease. An increase from 2.8 to 3.7% true protein caused scores for both appearance and texture descriptors to increase.