Ultrafiltration 99 minerals often are usually in the region of 0.1, but may be as high as 0.5, if the mineral binds to macromolecules. It is important to appreciate that any component with a rejection value greater than 0 will increase in concentration during the course of an ultrafiltration process. Rejection values can be used to check the integrity and performance of a membrane. Some values for components in dairy processing are given in Table 4. 1. Note the relatively high values for minerals, which suggests some binding to the proteins, particularly for calcium and magnesium. Membrane manufacturers some times present performance data in terms of rejection values of a range of components of different molecular weights(see Table 4.2). This will give some guidelines in terms of selection. However, very rarely are those components selected that one is interested in An alternative form of representation widely used is the molecular weight cut-off value. Table 4. 1. Rejection characteristics obtained during ultra filtration of dairy products Product Protein Lactose Ash Sweet whey 0.85-1.0 00.2 0-0.5 Ac 0.85-1.0 00.2 Skim milk 0.965-1.0 Whole milk 0.965-0.999 00.03 00.1 a Based on Kjeldahl nitrogen x 6.38 Taken from Lewis(1982) Table 4. 2. Some cited rejection characteristics for different components MW 3000 1000030000 100000 Insulin 600 >0.98 Cytochrome C 12400 045 >0.98 095 0.75 0.20 67000>0.980.98 0.95 Adapted from data from Amicon(1992) The molecular weight cut-off values for UF membranes range betv and 300 000. At values of about 2000, it overlaps with nanofiltration or loose reverse osmosis, whereas at 30 000 it overlaps with microfiltration. Generally the applied pressure required will decrease with increasing cut-off value and pressures in the range 1-15 bar are used It is implied that a membrane with a molecular weight cut-off of 5000, would reject all omponents with that molecular weight value or higher (R= 1)and allow components below that molecular weight to permeate freely. Often dextrins have been used for esti mating molecular weight cut-off, but these are linear molecules. However, due to theUltrafiltration 99 minerals often are usually in the region of 0.1, but may be as high as 0.5, if the mineral binds to macromolecules. It is important to appreciate that any component with a rejection value greater than 0 will increase in concentration during the course of an ultrafiltration process. Rejection values can be used to check the integrity and performance of a membrane. Some values for components in dairy processing are given in Table 4.1. Note the relatively high values for minerals, which suggests some binding to the proteins, particularly for calcium and magnesium. Membrane manufacturers some￾times present performance data in terms of rejection values of a range of components of different molecular weights (see Table 4.2). This will give some guidelines in terms of selection. However, very rarely are those components selected that one is interested in. An alternative form of representation widely used is the molecular weight cut-off value. Table 4.1. Rejection characteristics obtained during ultra￾filtration of dairy products Product Proteina Lactose Ash Sweet whey 0.85-1.0 0-0. 2 0-0.5 Acid whey 0.85-1.0 0-0.2 0-0.5 Skim milk 0.965-1 .O 0-0.2 0-0.5 Whole milk 0.965-0.999 0-0.03 0-0.1 a Taken from Lewis (1982). Based on Kjeldahl nitrogen x 6.38. Table 4.2. Some cited rejection characteristics for different components MW 3000 10 000 30 000 100 000 Insulin 6 000 >0.98 - - - Cytochrome C 12 400 >0.98 0.85 0.45 - a-Ch ymotrypsinogen 24 500 >0.98 0.95 0.75 0.20 Albumin 67 000 >0.98 >0.98 0.95 0.30 Adapted from data from Amicon (1992). The molecular weight cut-off values for UF membranes range between about 2000 and 300 000. At values of about 2000, it overlaps with nanofiltration or ‘loose reverse osmosis’, whereas at 30 000 it overlaps with microfiltration. Generally the applied pressure required will decrease with increasing cut-off value and pressures in the range 1-15 bar are used. It is implied that a membrane with a molecular weight cut-off of 5000, would reject all components with that molecular weight value or higher (R = 1) and allow components below that molecular weight to permeate freely. Often dextrins have been used for esti￾mating molecular weight cut-off, but these are linear molecules. However, due to the