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Cheese | Membrane Processing in Cheese Manufacture
Membrane Processing in Cheese Manufacture V V Mistry, South Dakota State University, Brookings, SD, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 1, pp 300–306, ª 2002, Elsevier Ltd.
Introduction Cheesemaking is a process of controlled removal of moisture from milk by acid and temperature manipulation. Ultimately, most of the casein, fat and insoluble minerals along with some water are retained in the cheese. The efficiency with which these components are retained is of great interest to cheese-makers because of the impact on cheese yield and therefore on the cost of production. Membrane processing provides the potential for improving the efficiency of cheesemaking and therefore offers capabilities that are of value in terms of economics and quality, and also provides opportunities for the development of new cheeses. Membrane processing, including reverse osmosis (also known as hyperfiltration), nanofiltration, ultrafiltration and microfiltration, are pressure-driven separation/concentration operations which employ organic or inorganic membranes. Reverse osmosis of milk or whey will remove only water and is therefore similar to thermal evaporation (Table 1). Nanofiltration removes water and small monovalent ions, such as sodium, potassium and chloride. Ultrafiltration achieves greater separation; in addition to water and smaller minerals, it also removes lactose and most water-soluble minerals and vitamins. Microfiltration, on the other hand, is able to separate larger components of milk such as proteins. It is therefore possible to separate caseins and whey proteins. Bacterial cells and spores can also be removed from milk with this process. This diverse range of separation capabilities is possible with the help of membranes of specific pore sizes and process parameters (pressure) (see Milk Protein Products: Membrane-Based Fractionation). Membraneprocessed milk or whey possesses unique compositional and physical characteristics that enable applications in the manufacture of various products. Cheese manufacture using membrane processing has been practiced commercially since the early 1970s but the manner in which it is used has evolved over time owing to experience gained by cheese-makers and the development of new membranes and applications. Membrane processes can be used in cheese manufacture to accomplish various specific tasks. The effects of reverse osmosis of milk are similar to those of thermal
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concentration of milk or fortification of milk with milk powder. The objective of such methods is to concentrate all milk components equally to a predetermined level. The later two methods (thermal concentration and fortification) are practiced in commercial cheese manufacture to improve the efficiency of cheesemaking and increase cheese yield. Reverse osmosis is generally not used for such applications because current multiple-effect evaporators equipped with vapor recompression systems offer greater efficiencies of operation, although combinations of thermal evaporation and reverse osmosis have been suggested for process optimization (see Plant and Equipment: Evaporators). Ultrafiltration and microfiltration are the most common membrane processes used in the cheese industry. Applications for nanofiltration, which is a relatively new membrane process in cheesemaking, are also being developed.
Ultrafiltration Ultrafiltration of milk is conducted at approximately 50 C but a lower or slightly higher temperature may also be used. The feed runs under pressure tangentially across an ultrafiltration membrane with a molecular weight cutoff of 10 000 to 100 000 Da. Low molecular weight materials, i.e. water, lactose, soluble minerals and vitamins, pass through the membrane and form the permeate stream. The membrane retains the remaining components and this mass, called retentate (or concentrate), is used for cheesemaking. The concentration of the retentate is varied by continually recycling the feed across the membrane until the desired concentration of milk proteins is achieved or by using a very large surface area of membrane, as in large commercial operations. There are three major methods for using ultrafiltration for cheesemaking; low concentration (also known as protein standardization), medium concentration, and high concentration (precheese concept). The latter (precheese concept) paved the way for the application of ultrafiltration in cheesemaking. This process, commonly known as the MMV process after its inventors Maubois, Mocquot and Vassal of INRA, France, was originally developed for
Cheese | Membrane Processing in Cheese Manufacture Table 1 Composition of milk concentrated approximately threefold by reverse osmosis and ultrafiltration
Component
Milk
Reverse osmosis (%)
Ultrafiltration
Total solids Fat Total protein Lactose Ash
12.2 3.50 3.20 4.80 0.70
36.6 10.5 9.6 14.4 2.1
28.0 10.5 9.5 4.1 1.3
Camembert cheese in the late 1960s and has been adapted for other cheeses, such as Feta. Certain physicochemical properties of ultrafiltered milk are particularly critical in cheesemaking applications and should be understood. These include viscosity, buffering capacity and rennet coagulation properties. As the protein content of milk is increased by ultrafiltration, there is an increase in viscosity. This aspect is of particular importance in the pumping requirements of ultrafiltered milk at high protein levels. For example, in some cheesemaking procedures where fermented milk is concentrated to a high level in a multistage ultrafiltration unit, positive displacement pumps have to be used to transport efficiently the viscous retentate across the later stages of the membrane unit. Further, mixing of ingredients such as starter, rennet and salt requires attention to prevent localized coagulation. During ultrafiltration of milk, proteins and colloidal salts are concentrated simultaneously. This causes an increase in the buffering capacity, and hence directly influences acid production characteristics of lactic acid bacteria, the pH of cheese, ripening characteristics and rennet coagulation. Under conditions of high buffering, it is difficult to obtain the desired pH even with the production of large amounts of lactic acid by the starter bacteria (Figure 1). Such a reduction in the rate at which the pH falls allows lactic acid bacteria to grow to large numbers but also offers the potential for growth of spoilage and pathogenic organisms. The large amount of lactic acid 7.0 2 6.6 pH
1.2
5.8 5.4
0.8
5.0
0.4
4.6
% TA
1.6
6.2
0 0
1
2
3
4
5
6
7
8
9 10 11
Hours
Figure 1 Relationship between lactic acid production (solid line) and pH (broken line) during lactic fermentation of unconcentrated milk (N ) and 4.3x ultrafiltered milk (&).
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produced results in an acid-tasting product and an imbalance in calcium will cause poor cheese texture and functionality, such as stretching. It is possible to lower the buffering capacity of ultrafiltered milk by removing some of the colloidal salts by solubilization. This can be accomplished by reducing the pH of milk to 5.6–6 during ultrafiltration. Another property of concern is rennet coagulation. Generally, concentration reduces the rennet coagulation time and increases the firmness of the coagulum. The firmness of rennet curd from unconcentrated whole milk, as measured by a formagraph, is approximately 8 mm after 40min while that of 6% protein ultrafiltered milk is 58 mm. This is in part because of increased protein and calcium in the retentate and also because in ultrafiltered milk (4) hydrolysis of only 50% of the -casein is required for curd formation compared to 97% for unconcentrated milk. This phenomenon is useful where high temperature treatment of milk, such as UHT, is used. It is well known that severely heated milk has poor rennet coagulation properties, i.e. the coagulum is very weak. French workers have demonstrated that if milk is ultrafiltered prior to UHT treatment, its rennet coagulation properties are restored.
Low-Concentration Retentates (Protein Standardization) At present, this is probably the most widely used application of ultrafiltration for cheesemaking because it is easily adaptable to most cheese varieties while at the same time providing economical benefits. In this method, milk is ultrafiltered to a concentration of no more than 2 and conventional cheesemaking equipment is used. A common practice is to increase the milk protein concentration to 3.7–4.5% prior to cheesemaking. This enables uniformity in the composition of milk, hence the term ‘protein standardization’ for this application of ultrafiltration. Other terms used include low-concentrated retentates (LCR). This method is used for various cheeses, including Camembert, Cheddar and Mozzarella. Advantages of using this procedure include uniformity in milk composition from day to day, a firm coagulum and therefore lower losses of casein to whey, increased cheese yield (approximately 6% on a protein basis), improved cheesemaking efficiency (more cheese per vat) and, importantly, there is no need for additional specialized cheesemaking equipment other than an ultrafiltration unit (Figure 2). The increase in cheese yield is attributed to better fat and protein recovery and the retention of some whey proteins. For cheeses such as Cheddar, concentration of up to 1.6 to 1.7 is used. At higher levels, the rennet coagulum is extremely firm and difficult to handle and fat losses in the whey may be high. The moisture content of Cheddar
4 5 3
6
7
1 8 9
2 10
Figure 2 Typical plant layout for Cheddar cheese manufacture using ultrafiitration for protein standardization. 1, Pasteurization and fat standardization; 2, protein standardization using UF; 3, cheesemaking; 4, draining conveyer; 5, cheddaring conveyor; 6, salting/mellowing conveyor; 7, block former; 8, vacuum packaging; 9, cheese block packing; 10, main process control panel. (Courtesy APV Nordic, Aarhus, Denmark.)
Cheese | Membrane Processing in Cheese Manufacture
cheese made with this process tends to decrease with protein content in milk; suggested reasons for this effect include rapid syneresis because of the coarser network of the protein gel. Using standard procedures such as lowtemperature cooking can increase moisture content. Researchers in the United States have demonstrated that homogenization of the cream can readily increase the level of cheese moisture. This method can also be used to increase further the yield of Cheddar cheese made from ultrafiltered milk. Recovery of fat in Cheddar cheese made from milk ultrafiltered to 4.6% protein and without cream homogenization was 94.7%, whereas that with cream homogenization was 96.8%. Maubois and colleagues in France developed the concept of ultrafiltration of milk on farms for cheesemaking in the late 1970s. This method used the LCR approach and involved the ultrafiltration of milk to less than 2 on the farm prior to transportation to the cheese factory. Permeate was fed to cows at the farm. The objective was to reduce the cost of transport of milk and to increase cheese yield. The economics of the process should also take into account the disposal of permeate that is produced on the farm. Subsequent studies in the United States suggested that this process would be economical for farms with 100 to 1000 cows. This method of ultrafiltering milk on the farm is now being used in the United States where milk is ultrafiltered cold to 3.5 at a collection centre and then transported long distances (>500 km) to cheese factories, at which the retentate is used to raise the total solids content of cheese milk to 13.5–15%.
Medium-Concentration Retentates In this method, milk is concentrated to 2 to 5 prior to cheesemaking. In some instances, diafiltration may be adopted to adjust the mineral content and buffering capacity. Much higher quantities of whey proteins are retained in the cheese and the yield is also higher than with the LCR method. The changes in the physicochemical properties of milk are large enough to warrant the use of specially designed equipment. The rennet-induced coagulum, for example, is very firm and difficult to handle with conventional equipment. After various industrial trials, commercial application of this method for cheesemaking is currently limited; the most notable example includes the APV-SiroCurd process for Cheddar cheese. This method was developed in Australia and involved continuous rennet coagulation of milk ultrafiltered to 40–45% solids. A small portion of the ultrafiltered milk was prefermented with lactic acid bacteria and used as bulk starter at the level of 10–12%. The continually forming coagulum was cut with specially designed wire knives and cubed curd pieces transferred into a rotating drum where syneresis took place during
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heating to 38 C over a 30–40 min period. Automated cheddaring occurred at the optimum pH, followed by milling and salting. Yield increases of 6–8% were claimed with this process. After several years of operation, however, this process is no longer used because of technical difficulties and poor economics.
Production of Liquid Precheese This method was the earliest of all ultrafiltration applications for cheesemaking. Milk is ultrafiltered to a concentration that is equal to the composition of the cheese being manufactured. It is then set with rennet, and acid development takes place, followed by additional treatments required for the specific cheese variety and there is very little whey separation. Thus, this process is unique in that practically no conventional cheesemaking equipment is required and of all the ultrafiltration methods, this method has the highest yield potential because of maximum whey protein retention in the cheese. While the protein standardization technique can be adapted to most cheese varieties, the liquid precheese concept is more limited in its applicability because it is not possible to achieve the composition of all cheeses by ultrafiltration. The process developed for this method was originally for Camembert cheese. It has also been applied to Feta cheese. New cheeses, such as Pave d’Affinois, have also been developed using the liquid precheese concept. For Camembert cheesemaking using this method, pasteurized milk is ultrafiltered to 5 and at 20 C a mesophilic lactic culture and salt are added at 2% and 0.75%, respectively. After a pH of 5.5 is reached, rennet is added and the mixture transferred to forms in which the coagulum is formed. At the proper firmness, the coagulum is removed from the molds, brined for 30min, sprayed with Penicillium camemberti spores and ripened at 11–12 C for 12 days at high humidity for mold growth on the surface of the cheese wheels. This process results in a yield increase of 12% to 15%. A high level of success with the liquid precheese concept has also been achieved with Feta cheese. In this Danish procedure, 5 ultrafiltered whole milk is homogenized, blended with lactic starter, salt and a lipaserennet mixture and poured into 18-kg tins where curd forms. The curd is then covered with salt or 6% brine and held for ripening. This process is an example in which the cheese is actually manufactured in its retail package. Recently, a process for the manufacture of blue cheese was commercialized in France in which standardized milk is ultrafiltered to 6. Starter and rennet are added and continuous coagulation, cutting and molding follow.
622 Cheese | Membrane Processing in Cheese Manufacture
Application of Ultrafiltration for Fresh Cheeses The manufacture of fresh acid-type cheeses, such as cream cheese, quark and Ricotta, was particularly challenging until mineral and ceramic membranes became available. These membranes made it possible to ultrafilter acid curd to a high solids level with few fouling problems. The general principle is to ferment high-heattreated milk to pH 4.6 to 4.8 and then ultrafilter the curd to the desired concentration. Traditionally, for quark, a centrifugal separator is used to separate curd and whey. The advantage of the ultrafiltration procedure is that whey proteins are retained and therefore cheese yield is increased. For cream cheese, the Cornell procedure involves the blending of heavy cream with 27.5% solids skim milk retentate to achieve the composition of cream cheese. This mixture is pasteurized and homogenized, then fermented, mixed with stabilizers and pasteurized.
Characteristics of Cheese from Ultrafiltered Milk While the retention of whey proteins is advantageous from the cheese yield perspective, its impact on cheese quality should also be taken into account. Whey proteins generally are inert filler materials and undergo very little proteolysis during ageing. Flavor development is therefore slow. Retarded proteolysis, along with the high water binding capacity of whey proteins, also influences the texture of cheese. Furthermore, the high buffering capacity of such cheese retards autolysis of lactic starter cells and the breakdown of casein. These effects become more pronounced as the concentration of whey proteins in cheese is increased (LCR cheese versus liquid precheese concept). The impact of high mineral retention on cheese functionality and flavor is also of concern. Excessive retention of calcium makes it difficult to obtain optimal functionality in cheeses such as Mozzarella and may lead to bitterness in fresh acid-curd cheeses. Bitterness also arises because of increased buffering, which leads to high levels of starter cells. Preacidification during ultrafiltration can control the mineral content of cheese.
makes it possible to achieve the desired specific separation, as well as fractionation, of milk constituents. Ceramic microfiltration membranes are commonly used but polysulfone membranes are also available. The current direct applications of microfiltration for cheesemaking include a process for the removal of bacteria and casein standardization of cheese milk. Both these approaches are commercialized.
Removal of Bacteria Reducing the microbial load of milk prior to cheesemaking by processes such as pasteurization is a common practice and in some cases even mandatory. On the other hand, high heat treatment of milk is believed to alter the cheesemaking characteristics of milk and flavor characteristics of cheese. High-speed centrifugation of milk (bactofugation) was developed to remove bacteria, particularly spores of Clostridium tyrobutyricum, from milk but the process is not as efficient as newly developed microfiltration procedures. The microfiltration process of Alfa Laval (now Tetra Pak) for removing bacteria and spores is called the Bactocatch process (Figure 3). Raw skim milk is microfiltered using a membrane with a pore size of 1.4 mm at 35–50 C. The retentate contains bacteria and the permeate is the bacteria-free milk. This bacteria-free milk can be blended with heated cream for standardization of fat. Bacteria removal efficiencies of 99.6–99.98% are reported, i.e. almost sterile milk is obtained. In the original Alfa Laval (Tetra Pak) procedure, the retentate (which contains bacteria and some milk components) was heated to a high temperature to kill the bacteria and blended with cream. In a modification developed by
Raw whole milk
Cream (10 parts)
Skim milk (90 parts) Microfilter (1.4 µm pore size)
Heat
Retentate (9 parts) (bacteria) Microfiltrate (81 parts) (protein)
Microfiltration Blend
Microfiltration of milk for cheesemaking is a relatively new concept but is rapidly gaining commercial acceptance because of the potential to use a wide range of membrane pore sizes (0.05–10 mm). This flexibility
Cheesemilk
Figure 3 Process for removal of bacteria from milk by microfiltration.
Cheese | Membrane Processing in Cheese Manufacture
APV, this bacterial concentrate is recycled through the self-desludging separator prior to microfiltration. Hence, bacteria are removed as sludge and milk components are recovered. This process is particularly suitable for fluid milk production (see Milk Protein Products: MembraneBased Fractionation) but is attractive for the manufacture of cheeses such as Swiss because of the possibility of removal of spores of Cl. tyrobutyricum without using nitrates or excessively high heat. On the other hand, French researchers have demonstrated that under normal circumstances, microfiltered milk is not ideal for eye formation in Swiss cheese because of the removal of non-starter lactic acid bacteria by microfiltration. This has been overcome by modifying the starter system. Specific heterolactic strains with mesophilic, thermophilic and propionic starters are recommended.
Casein Standardization Separation of casein and whey proteins can be accomplished by using a microfiltration membrane of 0.1 mm pore size. When skim milk is microfiltered in this manner, casein is concentrated and whey proteins are in the permeate. The casein content of milk is increased from 2.5% to 3.5% and hence cheese yield is increased. Furthermore, the microfiltrate (permeate) generated from this process contains whey proteins but no glycomacropeptide, which is normally found in whey from conventional cheesemaking procedures. With this method, it is therefore possible to standardize the casein content of cheese milk while producing an ‘ideal whey’ that has better functional characteristics than whey containing glycomacropeptides. In recent work, French workers have used this approach in combination with ultrafiltration to improve the cheesemaking properties of dried milk. In this patented process, whey proteins are completely or partially removed from milk by microfiltration, as above. The microfiltration permeate, which contains the whey proteins, is ultrafiltered and the permeate from ultrafiltration, which contains lactose, minerals and water, is blended with the retentate of microfiltration. The microfiltration retentate contains casein, and when blended with ultrafiltration permeate yields milk with low or no whey protein. This milk is evaporated and spray-dried. The spray-dried product can be used for cheesemaking after reconstitution without the typical difficulties encountered with conventional powder, which contains denatured whey proteins because of the heat treatments employed during manufacture.
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Nanofiltration Dairy applications of nanofiltration are very recent and major use is currently in the area of whey processing. Such use includes demineralization and concentration of whey and reduction of salt from salt whey (see Whey Processing: Demineralization). Interesting applications for cheese are also emerging. High permeability of monovalent ions (40–90%) and low permeability of polyvalent ions (5–20%) typically characterize nanofiltration. Consequently, it is possible to concentrate milk by nanofiltration to obtain an altered mineral balance. Experimental work suggests that this would offer potential for soft cheese manufacture.
Future Potential Over the past 35 years, membrane processing of milk has allowed the introduction of many innovations for cheesemaking. Not only has cheesemaking efficiency improved but also new cheeses have been developed. The process that led the development of membrane applications in cheesemaking, MMV process for Camembert cheese, is no longer used for this cheese because of difficulties in meeting consumer expectations for the appearance of the cheese. However, that process inspired the development of applications for other cheeses, namely, Feta, Pave´ d’Affinois, Le Petit Moule´, La Roche (blue cheese) and others. Since the early days, significant improvements have been made in membrane design and processes that have further enhanced cheesemaking applications. As new membrane processes and applications are developed, innovations in cheesemaking will continue. Unfortunately, not all countries have taken advantage of the applications of membranes for cheesemaking because the standards of identity pertaining to membrane-processed milk have not been fully resolved in individual countries but Codex Alimentarius regulations do permit the use of such milk and progress will continue. See also: Milk Protein Products: Membrane-Based Fractionation; Plant and Equipment: Evaporators; Whey Processing: Demineralization.
Further Reading Bylund G (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing Systems AB. Garem A, Schuck P, and Maubois JL (2000) Cheese-making properties of a new dairy based powder made by a combination of microfiltration and ultrafiltration. Lait 80: 25–32. Guinee TP, O’Callaghan DJ, Mulholland EO, and Harrington D (1996) Milk protein standardization by ultrafiltration for Cheddar cheese manufacture. Journal of Dairy Research 63: 281–293.
624 Cheese | Membrane Processing in Cheese Manufacture IDF (1992) New Applications of Membrane Processes. Special Issue no. 9201. Brussels: IDF. Kosikowski FV and Mistry W (1997) Cheese and Fermented Milk Poods, 3rd edn. Great Falls: FV Kosikowski LLC. Lawrence RC (1989) The Use of Ultrafiltration Technology in Cheesemaking. International Dairy Federation Bulletin no. 240. Brussels: IDF. Maubois JL (1998) Fractionation of milk proteins. Proceedings of the 25th International Dairy Congress, Aarhus: Denmark. pp. 74–86. Maubois JL, Mocquot G and Vassal L (1969) A Method for Processing Milk and Milk Products. French Patent no. 2 052 121.
Mistry VV and Maubois JL (1993) Application of membrane separation technology to cheese production. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology, vol. 1, pp. 493–522. New York: Chapman & Hall. Oommen BS, Mistry VV, and Nair MG (2000) Effect of homogenization of cream on composition, yield, and functionality of Cheddar cheese made from milk supplemented with ultrafiltered milk. Lait 80: 77–92. Rattray W and Jelen P (1996) Protein standardization of milk and dairy products. Trends in Food Science and Technology 7: 227–234. Saboya LV and Maubois JL (2000) Current developments of microfiltration technology in the dairy industry. Lait 80: 541–554.
Introduction Cheesemaking is a process of controlled removal of moisture from milk by acid and temperature manipulation. Ultimately, most of the casein, fat and insoluble minerals along with some water are retained in the cheese. The efficiency with which these components are retained is of great interest to cheese-makers because of the impact on cheese yield and therefore on the cost of production. Membrane processing provides the potential for improving the efficiency of cheesemaking and therefore offers capabilities that are of value in terms of economics and quality, and also provides opportunities for the development of new cheeses. Membrane processing, including reverse osmosis (also known as hyperfiltration), nanofiltration, ultrafiltration and microfiltration, are pressure-driven separation/concentration operations which employ organic or inorganic membranes. Reverse osmosis of milk or whey will remove only water and is therefore similar to thermal evaporation (Table 1). Nanofiltration removes water and small monovalent ions, such as sodium, potassium and chloride. Ultrafiltration achieves greater separation; in addition to water and smaller minerals, it also removes lactose and most water-soluble minerals and vitamins. Microfiltration, on the other hand, is able to separate larger components of milk such as proteins. It is therefore possible to separate caseins and whey proteins. Bacterial cells and spores can also be removed from milk with this process. This diverse range of separation capabilities is possible with the help of membranes of specific pore sizes and process parameters (pressure) (see Milk Protein Products: Membrane-Based Fractionation). Membraneprocessed milk or whey possesses unique compositional and physical characteristics that enable applications in the manufacture of various products. Cheese manufacture using membrane processing has been practiced commercially since the early 1970s but the manner in which it is used has evolved over time owing to experience gained by cheese-makers and the development of new membranes and applications. Membrane processes can be used in cheese manufacture to accomplish various specific tasks. The effects of reverse osmosis of milk are similar to those of thermal
618
concentration of milk or fortification of milk with milk powder. The objective of such methods is to concentrate all milk components equally to a predetermined level. The later two methods (thermal concentration and fortification) are practiced in commercial cheese manufacture to improve the efficiency of cheesemaking and increase cheese yield. Reverse osmosis is generally not used for such applications because current multiple-effect evaporators equipped with vapor recompression systems offer greater efficiencies of operation, although combinations of thermal evaporation and reverse osmosis have been suggested for process optimization (see Plant and Equipment: Evaporators). Ultrafiltration and microfiltration are the most common membrane processes used in the cheese industry. Applications for nanofiltration, which is a relatively new membrane process in cheesemaking, are also being developed.
Ultrafiltration Ultrafiltration of milk is conducted at approximately 50 C but a lower or slightly higher temperature may also be used. The feed runs under pressure tangentially across an ultrafiltration membrane with a molecular weight cutoff of 10 000 to 100 000 Da. Low molecular weight materials, i.e. water, lactose, soluble minerals and vitamins, pass through the membrane and form the permeate stream. The membrane retains the remaining components and this mass, called retentate (or concentrate), is used for cheesemaking. The concentration of the retentate is varied by continually recycling the feed across the membrane until the desired concentration of milk proteins is achieved or by using a very large surface area of membrane, as in large commercial operations. There are three major methods for using ultrafiltration for cheesemaking; low concentration (also known as protein standardization), medium concentration, and high concentration (precheese concept). The latter (precheese concept) paved the way for the application of ultrafiltration in cheesemaking. This process, commonly known as the MMV process after its inventors Maubois, Mocquot and Vassal of INRA, France, was originally developed for
Cheese | Membrane Processing in Cheese Manufacture Table 1 Composition of milk concentrated approximately threefold by reverse osmosis and ultrafiltration
Component
Milk
Reverse osmosis (%)
Ultrafiltration
Total solids Fat Total protein Lactose Ash
12.2 3.50 3.20 4.80 0.70
36.6 10.5 9.6 14.4 2.1
28.0 10.5 9.5 4.1 1.3
Camembert cheese in the late 1960s and has been adapted for other cheeses, such as Feta. Certain physicochemical properties of ultrafiltered milk are particularly critical in cheesemaking applications and should be understood. These include viscosity, buffering capacity and rennet coagulation properties. As the protein content of milk is increased by ultrafiltration, there is an increase in viscosity. This aspect is of particular importance in the pumping requirements of ultrafiltered milk at high protein levels. For example, in some cheesemaking procedures where fermented milk is concentrated to a high level in a multistage ultrafiltration unit, positive displacement pumps have to be used to transport efficiently the viscous retentate across the later stages of the membrane unit. Further, mixing of ingredients such as starter, rennet and salt requires attention to prevent localized coagulation. During ultrafiltration of milk, proteins and colloidal salts are concentrated simultaneously. This causes an increase in the buffering capacity, and hence directly influences acid production characteristics of lactic acid bacteria, the pH of cheese, ripening characteristics and rennet coagulation. Under conditions of high buffering, it is difficult to obtain the desired pH even with the production of large amounts of lactic acid by the starter bacteria (Figure 1). Such a reduction in the rate at which the pH falls allows lactic acid bacteria to grow to large numbers but also offers the potential for growth of spoilage and pathogenic organisms. The large amount of lactic acid 7.0 2 6.6 pH
1.2
5.8 5.4
0.8
5.0
0.4
4.6
% TA
1.6
6.2
0 0
1
2
3
4
5
6
7
8
9 10 11
Hours
Figure 1 Relationship between lactic acid production (solid line) and pH (broken line) during lactic fermentation of unconcentrated milk (N ) and 4.3x ultrafiltered milk (&).
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produced results in an acid-tasting product and an imbalance in calcium will cause poor cheese texture and functionality, such as stretching. It is possible to lower the buffering capacity of ultrafiltered milk by removing some of the colloidal salts by solubilization. This can be accomplished by reducing the pH of milk to 5.6–6 during ultrafiltration. Another property of concern is rennet coagulation. Generally, concentration reduces the rennet coagulation time and increases the firmness of the coagulum. The firmness of rennet curd from unconcentrated whole milk, as measured by a formagraph, is approximately 8 mm after 40min while that of 6% protein ultrafiltered milk is 58 mm. This is in part because of increased protein and calcium in the retentate and also because in ultrafiltered milk (4) hydrolysis of only 50% of the -casein is required for curd formation compared to 97% for unconcentrated milk. This phenomenon is useful where high temperature treatment of milk, such as UHT, is used. It is well known that severely heated milk has poor rennet coagulation properties, i.e. the coagulum is very weak. French workers have demonstrated that if milk is ultrafiltered prior to UHT treatment, its rennet coagulation properties are restored.
Low-Concentration Retentates (Protein Standardization) At present, this is probably the most widely used application of ultrafiltration for cheesemaking because it is easily adaptable to most cheese varieties while at the same time providing economical benefits. In this method, milk is ultrafiltered to a concentration of no more than 2 and conventional cheesemaking equipment is used. A common practice is to increase the milk protein concentration to 3.7–4.5% prior to cheesemaking. This enables uniformity in the composition of milk, hence the term ‘protein standardization’ for this application of ultrafiltration. Other terms used include low-concentrated retentates (LCR). This method is used for various cheeses, including Camembert, Cheddar and Mozzarella. Advantages of using this procedure include uniformity in milk composition from day to day, a firm coagulum and therefore lower losses of casein to whey, increased cheese yield (approximately 6% on a protein basis), improved cheesemaking efficiency (more cheese per vat) and, importantly, there is no need for additional specialized cheesemaking equipment other than an ultrafiltration unit (Figure 2). The increase in cheese yield is attributed to better fat and protein recovery and the retention of some whey proteins. For cheeses such as Cheddar, concentration of up to 1.6 to 1.7 is used. At higher levels, the rennet coagulum is extremely firm and difficult to handle and fat losses in the whey may be high. The moisture content of Cheddar
4 5 3
6
7
1 8 9
2 10
Figure 2 Typical plant layout for Cheddar cheese manufacture using ultrafiitration for protein standardization. 1, Pasteurization and fat standardization; 2, protein standardization using UF; 3, cheesemaking; 4, draining conveyer; 5, cheddaring conveyor; 6, salting/mellowing conveyor; 7, block former; 8, vacuum packaging; 9, cheese block packing; 10, main process control panel. (Courtesy APV Nordic, Aarhus, Denmark.)
Cheese | Membrane Processing in Cheese Manufacture
cheese made with this process tends to decrease with protein content in milk; suggested reasons for this effect include rapid syneresis because of the coarser network of the protein gel. Using standard procedures such as lowtemperature cooking can increase moisture content. Researchers in the United States have demonstrated that homogenization of the cream can readily increase the level of cheese moisture. This method can also be used to increase further the yield of Cheddar cheese made from ultrafiltered milk. Recovery of fat in Cheddar cheese made from milk ultrafiltered to 4.6% protein and without cream homogenization was 94.7%, whereas that with cream homogenization was 96.8%. Maubois and colleagues in France developed the concept of ultrafiltration of milk on farms for cheesemaking in the late 1970s. This method used the LCR approach and involved the ultrafiltration of milk to less than 2 on the farm prior to transportation to the cheese factory. Permeate was fed to cows at the farm. The objective was to reduce the cost of transport of milk and to increase cheese yield. The economics of the process should also take into account the disposal of permeate that is produced on the farm. Subsequent studies in the United States suggested that this process would be economical for farms with 100 to 1000 cows. This method of ultrafiltering milk on the farm is now being used in the United States where milk is ultrafiltered cold to 3.5 at a collection centre and then transported long distances (>500 km) to cheese factories, at which the retentate is used to raise the total solids content of cheese milk to 13.5–15%.
Medium-Concentration Retentates In this method, milk is concentrated to 2 to 5 prior to cheesemaking. In some instances, diafiltration may be adopted to adjust the mineral content and buffering capacity. Much higher quantities of whey proteins are retained in the cheese and the yield is also higher than with the LCR method. The changes in the physicochemical properties of milk are large enough to warrant the use of specially designed equipment. The rennet-induced coagulum, for example, is very firm and difficult to handle with conventional equipment. After various industrial trials, commercial application of this method for cheesemaking is currently limited; the most notable example includes the APV-SiroCurd process for Cheddar cheese. This method was developed in Australia and involved continuous rennet coagulation of milk ultrafiltered to 40–45% solids. A small portion of the ultrafiltered milk was prefermented with lactic acid bacteria and used as bulk starter at the level of 10–12%. The continually forming coagulum was cut with specially designed wire knives and cubed curd pieces transferred into a rotating drum where syneresis took place during
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heating to 38 C over a 30–40 min period. Automated cheddaring occurred at the optimum pH, followed by milling and salting. Yield increases of 6–8% were claimed with this process. After several years of operation, however, this process is no longer used because of technical difficulties and poor economics.
Production of Liquid Precheese This method was the earliest of all ultrafiltration applications for cheesemaking. Milk is ultrafiltered to a concentration that is equal to the composition of the cheese being manufactured. It is then set with rennet, and acid development takes place, followed by additional treatments required for the specific cheese variety and there is very little whey separation. Thus, this process is unique in that practically no conventional cheesemaking equipment is required and of all the ultrafiltration methods, this method has the highest yield potential because of maximum whey protein retention in the cheese. While the protein standardization technique can be adapted to most cheese varieties, the liquid precheese concept is more limited in its applicability because it is not possible to achieve the composition of all cheeses by ultrafiltration. The process developed for this method was originally for Camembert cheese. It has also been applied to Feta cheese. New cheeses, such as Pave d’Affinois, have also been developed using the liquid precheese concept. For Camembert cheesemaking using this method, pasteurized milk is ultrafiltered to 5 and at 20 C a mesophilic lactic culture and salt are added at 2% and 0.75%, respectively. After a pH of 5.5 is reached, rennet is added and the mixture transferred to forms in which the coagulum is formed. At the proper firmness, the coagulum is removed from the molds, brined for 30min, sprayed with Penicillium camemberti spores and ripened at 11–12 C for 12 days at high humidity for mold growth on the surface of the cheese wheels. This process results in a yield increase of 12% to 15%. A high level of success with the liquid precheese concept has also been achieved with Feta cheese. In this Danish procedure, 5 ultrafiltered whole milk is homogenized, blended with lactic starter, salt and a lipaserennet mixture and poured into 18-kg tins where curd forms. The curd is then covered with salt or 6% brine and held for ripening. This process is an example in which the cheese is actually manufactured in its retail package. Recently, a process for the manufacture of blue cheese was commercialized in France in which standardized milk is ultrafiltered to 6. Starter and rennet are added and continuous coagulation, cutting and molding follow.
622 Cheese | Membrane Processing in Cheese Manufacture
Application of Ultrafiltration for Fresh Cheeses The manufacture of fresh acid-type cheeses, such as cream cheese, quark and Ricotta, was particularly challenging until mineral and ceramic membranes became available. These membranes made it possible to ultrafilter acid curd to a high solids level with few fouling problems. The general principle is to ferment high-heattreated milk to pH 4.6 to 4.8 and then ultrafilter the curd to the desired concentration. Traditionally, for quark, a centrifugal separator is used to separate curd and whey. The advantage of the ultrafiltration procedure is that whey proteins are retained and therefore cheese yield is increased. For cream cheese, the Cornell procedure involves the blending of heavy cream with 27.5% solids skim milk retentate to achieve the composition of cream cheese. This mixture is pasteurized and homogenized, then fermented, mixed with stabilizers and pasteurized.
Characteristics of Cheese from Ultrafiltered Milk While the retention of whey proteins is advantageous from the cheese yield perspective, its impact on cheese quality should also be taken into account. Whey proteins generally are inert filler materials and undergo very little proteolysis during ageing. Flavor development is therefore slow. Retarded proteolysis, along with the high water binding capacity of whey proteins, also influences the texture of cheese. Furthermore, the high buffering capacity of such cheese retards autolysis of lactic starter cells and the breakdown of casein. These effects become more pronounced as the concentration of whey proteins in cheese is increased (LCR cheese versus liquid precheese concept). The impact of high mineral retention on cheese functionality and flavor is also of concern. Excessive retention of calcium makes it difficult to obtain optimal functionality in cheeses such as Mozzarella and may lead to bitterness in fresh acid-curd cheeses. Bitterness also arises because of increased buffering, which leads to high levels of starter cells. Preacidification during ultrafiltration can control the mineral content of cheese.
makes it possible to achieve the desired specific separation, as well as fractionation, of milk constituents. Ceramic microfiltration membranes are commonly used but polysulfone membranes are also available. The current direct applications of microfiltration for cheesemaking include a process for the removal of bacteria and casein standardization of cheese milk. Both these approaches are commercialized.
Removal of Bacteria Reducing the microbial load of milk prior to cheesemaking by processes such as pasteurization is a common practice and in some cases even mandatory. On the other hand, high heat treatment of milk is believed to alter the cheesemaking characteristics of milk and flavor characteristics of cheese. High-speed centrifugation of milk (bactofugation) was developed to remove bacteria, particularly spores of Clostridium tyrobutyricum, from milk but the process is not as efficient as newly developed microfiltration procedures. The microfiltration process of Alfa Laval (now Tetra Pak) for removing bacteria and spores is called the Bactocatch process (Figure 3). Raw skim milk is microfiltered using a membrane with a pore size of 1.4 mm at 35–50 C. The retentate contains bacteria and the permeate is the bacteria-free milk. This bacteria-free milk can be blended with heated cream for standardization of fat. Bacteria removal efficiencies of 99.6–99.98% are reported, i.e. almost sterile milk is obtained. In the original Alfa Laval (Tetra Pak) procedure, the retentate (which contains bacteria and some milk components) was heated to a high temperature to kill the bacteria and blended with cream. In a modification developed by
Raw whole milk
Cream (10 parts)
Skim milk (90 parts) Microfilter (1.4 µm pore size)
Heat
Retentate (9 parts) (bacteria) Microfiltrate (81 parts) (protein)
Microfiltration Blend
Microfiltration of milk for cheesemaking is a relatively new concept but is rapidly gaining commercial acceptance because of the potential to use a wide range of membrane pore sizes (0.05–10 mm). This flexibility
Cheesemilk
Figure 3 Process for removal of bacteria from milk by microfiltration.
Cheese | Membrane Processing in Cheese Manufacture
APV, this bacterial concentrate is recycled through the self-desludging separator prior to microfiltration. Hence, bacteria are removed as sludge and milk components are recovered. This process is particularly suitable for fluid milk production (see Milk Protein Products: MembraneBased Fractionation) but is attractive for the manufacture of cheeses such as Swiss because of the possibility of removal of spores of Cl. tyrobutyricum without using nitrates or excessively high heat. On the other hand, French researchers have demonstrated that under normal circumstances, microfiltered milk is not ideal for eye formation in Swiss cheese because of the removal of non-starter lactic acid bacteria by microfiltration. This has been overcome by modifying the starter system. Specific heterolactic strains with mesophilic, thermophilic and propionic starters are recommended.
Casein Standardization Separation of casein and whey proteins can be accomplished by using a microfiltration membrane of 0.1 mm pore size. When skim milk is microfiltered in this manner, casein is concentrated and whey proteins are in the permeate. The casein content of milk is increased from 2.5% to 3.5% and hence cheese yield is increased. Furthermore, the microfiltrate (permeate) generated from this process contains whey proteins but no glycomacropeptide, which is normally found in whey from conventional cheesemaking procedures. With this method, it is therefore possible to standardize the casein content of cheese milk while producing an ‘ideal whey’ that has better functional characteristics than whey containing glycomacropeptides. In recent work, French workers have used this approach in combination with ultrafiltration to improve the cheesemaking properties of dried milk. In this patented process, whey proteins are completely or partially removed from milk by microfiltration, as above. The microfiltration permeate, which contains the whey proteins, is ultrafiltered and the permeate from ultrafiltration, which contains lactose, minerals and water, is blended with the retentate of microfiltration. The microfiltration retentate contains casein, and when blended with ultrafiltration permeate yields milk with low or no whey protein. This milk is evaporated and spray-dried. The spray-dried product can be used for cheesemaking after reconstitution without the typical difficulties encountered with conventional powder, which contains denatured whey proteins because of the heat treatments employed during manufacture.
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Nanofiltration Dairy applications of nanofiltration are very recent and major use is currently in the area of whey processing. Such use includes demineralization and concentration of whey and reduction of salt from salt whey (see Whey Processing: Demineralization). Interesting applications for cheese are also emerging. High permeability of monovalent ions (40–90%) and low permeability of polyvalent ions (5–20%) typically characterize nanofiltration. Consequently, it is possible to concentrate milk by nanofiltration to obtain an altered mineral balance. Experimental work suggests that this would offer potential for soft cheese manufacture.
Future Potential Over the past 35 years, membrane processing of milk has allowed the introduction of many innovations for cheesemaking. Not only has cheesemaking efficiency improved but also new cheeses have been developed. The process that led the development of membrane applications in cheesemaking, MMV process for Camembert cheese, is no longer used for this cheese because of difficulties in meeting consumer expectations for the appearance of the cheese. However, that process inspired the development of applications for other cheeses, namely, Feta, Pave´ d’Affinois, Le Petit Moule´, La Roche (blue cheese) and others. Since the early days, significant improvements have been made in membrane design and processes that have further enhanced cheesemaking applications. As new membrane processes and applications are developed, innovations in cheesemaking will continue. Unfortunately, not all countries have taken advantage of the applications of membranes for cheesemaking because the standards of identity pertaining to membrane-processed milk have not been fully resolved in individual countries but Codex Alimentarius regulations do permit the use of such milk and progress will continue. See also: Milk Protein Products: Membrane-Based Fractionation; Plant and Equipment: Evaporators; Whey Processing: Demineralization.
Further Reading Bylund G (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing Systems AB. Garem A, Schuck P, and Maubois JL (2000) Cheese-making properties of a new dairy based powder made by a combination of microfiltration and ultrafiltration. Lait 80: 25–32. Guinee TP, O’Callaghan DJ, Mulholland EO, and Harrington D (1996) Milk protein standardization by ultrafiltration for Cheddar cheese manufacture. Journal of Dairy Research 63: 281–293.
624 Cheese | Membrane Processing in Cheese Manufacture IDF (1992) New Applications of Membrane Processes. Special Issue no. 9201. Brussels: IDF. Kosikowski FV and Mistry W (1997) Cheese and Fermented Milk Poods, 3rd edn. Great Falls: FV Kosikowski LLC. Lawrence RC (1989) The Use of Ultrafiltration Technology in Cheesemaking. International Dairy Federation Bulletin no. 240. Brussels: IDF. Maubois JL (1998) Fractionation of milk proteins. Proceedings of the 25th International Dairy Congress, Aarhus: Denmark. pp. 74–86. Maubois JL, Mocquot G and Vassal L (1969) A Method for Processing Milk and Milk Products. French Patent no. 2 052 121.
Mistry VV and Maubois JL (1993) Application of membrane separation technology to cheese production. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology, vol. 1, pp. 493–522. New York: Chapman & Hall. Oommen BS, Mistry VV, and Nair MG (2000) Effect of homogenization of cream on composition, yield, and functionality of Cheddar cheese made from milk supplemented with ultrafiltered milk. Lait 80: 77–92. Rattray W and Jelen P (1996) Protein standardization of milk and dairy products. Trends in Food Science and Technology 7: 227–234. Saboya LV and Maubois JL (2000) Current developments of microfiltration technology in the dairy industry. Lait 80: 541–554.