150 A.S. Grandison and T J. A. Finnigan reduced requirement for rennet and starter, and the ability to produce much more cheese per vat( Grandison and Glover, 1994). In most cases UF membranes have been used as it is necessary to retain all the protein in the concentrate, An alternative approach is to oncentrate the curd after coagulation of the milk in which case a solution of lactose and tion in the manufacture of some soft cheese type el. This can be done using centrifuga minerals is removed from the semi-solid protein However, the use of MF is an attractive alternative Rios et al. (1989) have carried out extensive trials on this application and concluded that the use of 0. 2 um pore diameter membranes gave a product with better texture and yield than with centrifugation. The choice of ceramic membranes allowed the curd to be contacted directly with the membrane Other food applications have been reported with meat and vegetable products includ ing the following Devereux and Hoare (1986) described the use of Mf to recover precipitated so protein. This could have advantages over recovery of the dissolved protein using UF. Gelatin is a proteinaceous material derived by hydrolysis of collagen. This is purified y filtration incorporating diatomaceous earth. The latter process can be replaced by CMF which effectively removes dirt, coagulated proteins, fats and other particulate materials from the feed. Again the CMF method gives higher yields of high quality product on a continuous basis. Short (1988)calculated that incorporating CMF plants for gelatin would have a payback time of 3 years for a capacity of 30 tonnes/h 5.3. 2 Applications for biotechnology Applications of MF in the biotechnology industry are very promising although the process has not yet made the breakthroughs that may have been expected. The major problem with MF of suspensions of cells or cell debris is the exponential flux decay resulting from adhesion of cells or cell fragments to the membrane -i.e. biofouling. This has limited the application of CMf into biotechnological downstream processing Solutions to this problem, other than general methods of avoiding fouling, are discussed by Defrise and Gekas(1988)and include choice of biocompatible membrane materials and the use of surfactants and polyelectrolytes. Most biotechnological applications of MF are as a competitor to centrifugation, and mF is becoming recognised as a viable alterna ive in many cases. CMF may have advantages over centrifugation when containment is required(e. g. when handling pathogenic organisms or in recombinant DNA technology) as aerosols are not produced during the operation( Kroner et al., 1984). The capital and maintenance costs of MF are lower than for centrifugation, although membrane replace ment is expensive. Tutunjian(1985) compared the costs of process-scale harvesting and washing of Escherichia coli cells using MF with a hollow fibre system to centrifugation The MF system had about 70% lower capital, and 25%o lower running costs than centrifugation. Also virtually 100%o recovery of solids is possible with MF, whereas it is often less than 90% with centrifugation CMF is a versatile technique for cell harvesting and cell debris removal during recovery of intracellular products. The viability and enzyme content of the cells is unaffected by MF, and it is possible to concentrate cell suspensions to 20-25% dr weight, limited by pumping considerations (Le and Atkinson, 1985). A 0 I um150 reduced requirement for rennet and starter, and the ability to produce much more cheese per vat (Grandison and Glover, 1994). In most cases UF membranes have been used as it is necessary to retain all the protein in the concentrate. An alternative approach is to concentrate the curd after coagulation of the milk in which case a solution of lactose and minerals is removed from the semi-solid protein gel. This can be done using centrifuga￾tion in the manufacture of some soft cheese types. However, the use of MF is an attractive alternative. Rios et al. (1989) have carried out extensive trials on this application and concluded that the use of 0.2 pm pore diameter membranes gave a product with better texture and yield than with centrifugation. The choice of ceramic membranes allowed the curd to be contacted directly with the membrane. Other food applications have been reported with meat and vegetable products includ￾ing the following. Devereux and Hoare (1986) described the use of MF to recover precipitated soya protein. This could have advantages over recovery of the dissolved protein using UF. Gelatin is a proteinaceous material derived by hydrolysis of collagen. This is purified by filtration incorporating diatomaceous earth. The latter process can be replaced by CMF which effectively removes dirt, coagulated proteins, fats and other particulate materials from the feed. Again the CMF method gives higher yields of high quality product on a continuous basis. Short (1988) calculated that incorporating CMF plants for gelatin would have a payback time of 3 years for a capacity of 30 tonnes/h. 5.3.2 Applications for biotechnology Applications of MF in the biotechnology industry are very promising although the process has not yet made the breakthroughs that may have been expected. The major problem with MF of suspensions of cells or cell debris is the exponential flux decay resulting from adhesion of cells or cell fragments to the membrane - i.e. biofouling. This has limited the application of CMF into biotechnological downstream processing. Solutions to this problem, other than general methods of avoiding fouling, are discussed by Defrise and Gekas (1988) and include choice of biocompatible membrane materials and the use of surfactants and polyelectrolytes. Most biotechnological applications of MF are as a competitor to centrifugation, and MF is becoming recognised as a viable alterna￾tive in many cases. CMF may have advantages over centrifugation when containment is required (e.g. when handling pathogenic organisms or in recombinant DNA technology) as aerosols are not produced during the operation (Kroner et d., 1984). The capital and maintenance costs of MF are lower than for centrifugation, although membrane replace￾ment is expensive. Tutunjian ( 1985) compared the costs of process-scale harvesting and washing of Escherichia coli cells using MF with a hollow fibre system to centrifugation. The MF system had about 70% lower capital, and 25% lower running costs than Centrifugation. Also virtually 100% recovery of solids is possible with MF, whereas it is often less than 90% with centrifugation. CMF is a versatile technique for cell harvesting and cell debris removal during recovery of intracellular products. The viability and enzyme content of the cells is unaffected by MF, and it is possible to concentrate cell suspensions to 20-25% dry weight, limited by pumping considerations (Le and Atkinson, 1985). A 0.1 pm A. S. Grandison and T. J. A. Finnigan