Ultrafiltration 105 for most food systems. Therefore it is very important to measure rejection data under the prevailing operating conditions Lewis(1982) has compiled rejection data for different systems. It was not al ways clear some confusion between the terms rejection and yield in some of the earlier repord R whether rejection data for proteins was based upon crude protein or true protein. U filtration could be useful for removing non-protein nitrogen. There also appeared Table 4. 1 shows some rejection data for some dairy products, reported by the Interna tional Dairy Federation (1979) Figure 4.3 shows rejection data taken during the batch ultrafiltration process during concentration of rapeseed meal, for crude protein, total solids and glucosinolates. For all components, there is an increase in rejection as concentration proceeds, with the increase being most marked between concentration factors of 1 and 2. Many investigators have reported similar increases in rejection as concentration proceeds Table 4.4 shows some data for the average rejection data for proteins and glucosinolate, extracted at different pH values, determined by the method above, Yield alues are also presented. In such complex systems the performance is also strongly affected by pH(see Sections 4.3.2 and 4.5.2) Table 4.4. Average rejection(Ray) and yield values for glucosinolates and crude protein during batch ultra filtration processes at different pH values Glucosinolate Crude protein 2.5 0.5000.45) 0.970.95) 0.39(0.38) 0.93(0.89) 7.0 0.28(0.31) 081(0.74) 9.0 0.36(0.36) 0.95(0.92) 11.0 0.44(041) 0.85(0.92) Yield values in brackets Glucosinolates are expressed as isothiocyanates Therefore on values are very important as they influence the nature of the separation obtained, as well as the yield (or loss)of components. These aspects assume greater importance as the value of the product increases. Changes in rejection during process could also be indicative of some important changes taking place at the surface of the membrane. The effects of pressure and temperature on rejection, as predicted by some f the models, are discussed in Chapter 3. Some practical problems associated with UF of proteins, such as adsorption and pH effects, are described by Sirkar and Prasad(1987) 4.3 PERFORMANCE OF ULTRAFILTRATION SYSTEMS Permeate flux In UF process applications, the two most important parameters are the membraneUltrafiltration 105 for most food systems. Therefore it is very important to measure rejection data under the prevailing operating conditions. Lewis (1982) has compiled rejection data for different systems. It was not always clear whether rejection data for proteins was based upon crude protein or true protein. Ultra￾filtration could be useful for removing non-protein nitrogen. There also appeared to be some confusion between the terms rejection and yield in some of the earlier reports. Table 4.1 shows some rejection data for some dairy products, reported by the Interna￾tional Dairy Federation (1979). Figure 4.3 shows rejection data taken during the batch ultrafiltration process during concentration of rapeseed meal, for crude protein, total solids and glucosinolates. For all components, there is an increase in rejection as concentration proceeds, with the increase being most marked between concentration factors of 1 and 2. Many investigators have reported similar increases in rejection as concentration proceeds. Table 4.4 shows some data for the average rejection data for proteins and glucosinolate, extracted at different pH values, determined by the method above. Yield values are also presented. In such complex systems the performance is also strongly affected by pH (see Sections 4.3.2 and 4.5.2). Table 4.4. Average rejection (Rav) and yield values for glucosinolates and crude protein during batch ultra￾filtration processes at different pH values. PH Glucosinolate Crude protein 2.5 0.50 (0.45) 0.97 (0.95) 3.5 0.39 (0.38) 0.93 (0.89) 7.0 0.28 (0.31) 0.81 (0.74) 9.0 0.36 (0.36) 0.95 (0.92) 11.0 0.44 (0.41) 0.85 (0.92) Yield values in brackets. Glucosinolates are expressed as isothiocyanates. Therefore, rejection values are very impofiant as they influence the nature of the separation obtained, as well as the yield (or loss) of components. These aspects assume greater importance as the value of the product increases. Changes in rejection during a process could also be indicative of some important changes taking place at the surface of the membrane. The effects of pressure and temperature on rejection, as predicted by some of the models, are discussed in Chapter 3. Some practical problems associated with UF of proteins, such as adsorption and pH effects, are described by Sirkar and Prasad (1987). 4.3 PEKFORMANCE OF ULTRAFILTRATION SYSTEMS Permeate flux In UF process applications, the two most important parameters are the membrane