The milk protein beverage category continues to grow and consumers are seeking variety. Ultrafiltration (UF) has seen increased use for production of milk-based beverages containing different fat and protein concentrations. A milk cryoscope is a commonly used rapid method for detection of water adulteration of milk (freezing point increases with water addition) and has also been confirmed as a rapid method to monitor enzymatic hydrolysis of lactose to glucose and galactose (freezing point decreases with increased lactose hydrolysis). UF is a commonly applied unit operation to concentrate protein in milk, and both lactose and soluble minerals are removed by that process. Ultrafiltration of milk can be monitored by mid infrared spectroscopy to measure protein and lactose or by enzymatic or HPLC methods for measuring lactose concentration, all of which are costly methods or are too slow for use in quality control in real time processing. Our objective was to develop and demonstrate a rapid method for monitoring lactose removal during UF using a milk cryoscope. Ultrafiltered milk retentates were manufactured at different lactose removals (ca. 0, 30, 70 and 98%) using UF in combination with diafiltration to determine the impact of 4 fat levels (ca. skim, 1%, 2% and 3.5% fat) and 3 protein levels (ca. 3.4, 6.5 and 10.5% true protein) on change in milk freezing point. These experiments were replicated twice followed by enzymatic analysis of lactose and milk freezing point determination. Freezing point increased linearly (R2 = 0.99, p&lt;0.05) with increased lactose and soluble minerals removal (i.e., decreased percent lactose). Prior to UF, milk freezing point was approximately -0.521oC, and when 96 to 98% of the lactose and soluble minerals were removed, the milk freezing point increased to - 0.0039oC, regardless of fat and protein content. Variation in background protein and fat concentration did not influence the ability to estimate the percent of lactose removal in UF milk using a cryoscope. A milk cryoscope would be a rapid (&lt; 3 min per measurement) and effective method to monitor a UF process to determine the completeness of removal of lactose.

Estimation of lactose removal by increase in freezing point during processing of milk by ultrafiltration

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