Ultrafiltration membrane separation is a promising technology for AMF fractionation. An experimental study has been presented in our earlier communication [1] to demonstrate the success of fractionation using a 20 g melted anhydrous milkfat (40 degrees C) charged in a dead-end filtration cell. The operating conditions determined were: temperature 30 degrees C, stirring speed 100 rpm, and constant filtration pressure 300 psi, for a processing time of around 30 min. However, under these conditions especially at 300 psi or higher pressure, milkfat flux exhibit continuous decline with time as a result of the gradual fouling. This is due to the gradual accumulation and deposition of fat nuclei and crystals on and in the membrane pores causing irreversible deformation in the membrane pores. This leads to gradual increase in the membrane resistance for milkfat permeation. In this paper, a mathematical model is presented for the calculations of milkfat flux decline using the experimental parameters. The average predicted milkfat flux is 3.53E-06 m(3) m(-2) s(-1), while the experimental value is 3.16E-06 m(3) m(-2) s(-1), giving a reasonable error (10.5%). Thus, this model can be used for the prediction of milkfat flux under any processing conditions within the range considered here. Furthermore, the model enables us to determine the development of the cake layer thickness with time, the mass of fat deposited per unit membrane area (kg m(-2)), and the average specific filtration resistance. (c) 2006 Elsevier B.V. All rights reserved.