Changes in the Chemical Composition During Ultrafiltration of Skim Milk

Five batches of pasteurized skim milk were concentrated to approximately 2-, 4-, and 5-fold by UF.Chemical analyses of the skim milk and retentates were done to determine the change in chemical composition that occurred during UF.Milk proteins were concentrated during UF from an average 3.42% in skim milk 5-fold retentates, respectively.Milk fat similarly was concentrated from .11% in skim milk to .24,.45,and .60% in 2-, 4, and 5-fold retentates, respectively.Lactose content progressively decreased during UF from an initial 5.06% in skim 4-, and 5-fold retentates, respectively.Total solids content increased to a lesser extent, compared with protein and fat, from 9.19% in skim milk to 12.72, 17.80, and 23.91% in 2-, 4, and 5-fold retentates, respectively, reflecting the loss of lactose and other soluble small molecular weight components.Analysis of the following minerals indicated partial concentration: Ca* by 1.6-, 3.0-, and 4.3-fold; 1.8-, 3.4, and 4.9-fold; Few by 1.9-, 3.5-, and 4.9-fold; Cu++ by 1.7-, 2.0-, and 3.0-fold in the 2-, 4-, and 5-fold retentates, respectively.Microbiological assays indicated decreases in the following B vitamins: thiamin by 57, 77, to 6.85, 13.51, and 17.1% in 2-, 4, and milk to 4.76, 4.29, and 4.06% in 2-, Mg* by 1.4-, 2.3-, and 3.O-fold; Zn* by 3.4-, and 4.7-fold; and Mn* by 1.5,