801

Journal of Food Protection, Vol. 54, No. 10, Pages 801-809 (October 1991) Copyright© International Association of , Food and Environmental Sanitarians

Ultrafiltration and Reverse Osmosis in Technology: A Review

FATHY E. EL-GAZZAR and ELMER H. MARTH* Department of Food Science and The Food Research Institute, University of Wisconsin-Madison, Madison, Wisconsin 53706 Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 (Received for publication January 11, 1991)

ABSTRACT no higher than 35°C. These conditions impose limitations on cleaning procedures that can be used industrially. Be­ Ultrafiltration and reverse osmosis processes can be useful in cause of these limitations cellulose acetate has now been the dairy foods industry. When milk is processed, milk fat and superseded by other polymers more tolerant to pH and casein are rejected fully (e.g., are in retentate) and thus are temperature. Polyamides were used for some time since concentrated by ultrafiltration and reverse osmosis membranes. they are better able to handle higher temperatures and a Lactic cultures are slow to reduce the pH of retentate because of wider pH range than is cellulose acetate. Polysulfones, its increased buffering capacity since concentrated calcium phos­ which are now frequently used, are a better alternative phate and proteins are present. Conditions for growth of patho­ genic microorganisms and inhibition of such bacteria in ultrafiltered because they have excellent hydrogen-bonding capabilities milk differ from those of unfiltered milk. The principal advantage and are very strong and rigid when wet. They can tolerate of using ultrafiltered milk for conversion into such as temperatures up to 100°C and pH values from 1-14. Cheddar, cottage, Havarti, Feta, brick, Colby, and Domiati is an Polysulfone membranes also are more resistant to chlorine increase in yield of product. Additional benefits claimed for use than is cellulose acetate. of ultrafiltered milk in making include reduction in costs Glover (22) also stated that membrane structure may of energy, equipment, and labor; improved consistency of cheese be of three types, (a) The structure is asymmetric when the flavor; and possible production of new byproducts. membrane is of the same material throughout, but has a thin tight skin on the surface on the feed side so that the skin is the effective ultrafiltration layer. The more open and ULTRAFILTRATION: INTRODUCTION AND thicker sublayers serve as a support for the skin. Asymmet­ DEFINITION ric membranes are currently most widely used for ultrafil­ tration. (b) The structure is symmetrical when the material Ultrafiltration is a sieving process that employs a is identical throughout the membrane; such membranes are membrane with definite pores that are large enough to used for experimental purposes, (c) Composite asymmetric permit the passage of water and small molecules. When membranes are composed of two different materials, the pressure is applied to a fluid, the semipermeable membrane thin layer of polymer to serve as the filtering membrane, allows small species to pass through as permeate and larger and the second is a layer of another porous material. An species are retained and concentrated as retentate. In ultra­ asymmetric membrane has a total thickness up to 100 ^m, filtration of milk, nonprotein nitrogen and soluble compo­ 20-100 ^m for the thick supporting layer and 0.1-1 ^m for nents such as lactose, salts, and some vitamins pass through the tight thin layer, which has pores 2-20 nm in diameter. the membrane, whereas milk fat, protein, and insoluble Geometrically, membranes are tubular, flat, or spirally salts are retained by the membrane (22,57). wound. The tubular membrane is easily cleaned since there The ultrafiltration membrane is the most important part are no dead spaces. However, it has some disadvantages of any ultrafiltration system. Glover (22) indicated that the such as high hold-up volume per unit of membrane area, two most important characteristics that any membrane and equipment occupies a large amount of space per unit of material should have are (a) ability to hydrogen bond to membrane area. Flat or spirally wound membranes have a water thus enabling water to enter the membrane and (b) low hold-up volume per unit of membrane area and equip­ high wet strength. ment occupies a small amount of space per unit of mem­ There are several polymers which can be used to brane area. The spiral system consumes less energy for produce membranes. The first to be used was a polymer of pumping than do tubular systems. Flat or spirally wound cellulose acetate. Faults were found with this material, membranes are difficult to clean if badly fouled. Another however, because it is intolerant to chlorine and can only version of the tubular system has membrane tubes less than be used over a limited pH range of 3-7 and at a temperature 1 mm in diameter, which are known as hollow fibers rather

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 802 EL-GAZZAR AND MARTH than tubes. The hollow fiber design has low capital costs, ultrafiltration potentially can reduce by up to 80% the provides an excellent membrane area per volume, and quantity of coagulant commonly used to prepare a given membrane replacement is easy. However, it does not readily weight of cheese. This results in decreased processing costs lend itself to processing suspensions as particulate matter for the cheese maker. The reduction in amount of coagulant can foul or block the fibers. needed also can help alleviate the worldwide shortage of Ultrafiltration of milk before cheesemaking was first natural calf rennet, although regulatory approval and com­ proposed by Maubois et al. (47). Advantages claimed for mercial introduction of chymosin produced biotech- ultrafiltration technology in cheese manufacturing are in nologically minimizes this benefit of ultrafiltration. the following areas: (a) Yield: The principal advantage of Moreover, making cheese from ultrafiltered milk can the process is an increase in yield of cheese. This increase be controlled automatically and then avoids many of the results from retention in the cheese of proteins which are manipulations of traditional cheesemaking technology; re­ not coagulated by rennet, i.e., the so-called soluble proteins duction in labor costs also can be expected. As with making ( or serum proteins) of milk (45). Maubois et al. (48) cheese from unfiltered milk, the process can be made found when cheese is made traditionally, 77 of 100 g of continuous by use of appropriate equipment for ultrafiltra­ tion of milk and coagulating, molding, and salting of . nitrogenous substances from milk remain in soft ripened Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 cheese and 83 of 100 g in soft fresh cheese (67). The (d) Pollution: The ultrafiltrate (new whey or permeate) difference (23 or 17 g) represents a mixture of protein and contains virtually no proteins or milk fat and thus its nonprotein nitrogenous substances which passes into whey biological oxygen demand is only 80% of that of traditional during conventional cheesemaking. whey. Furthermore, permeate has a pH identical to that of During ultrafiltration, only the nonprotein nitrogen milk, 6.5 to 6.7. Permeate can be collected under aseptic passes through the membrane (about 5% of the nitrogenous conditions, and thus initially contains no or few microor­ substances of the milk). All the milk proteins, whether they ganisms. Although uses for permeate may be limited, it are casein or whey proteins, remain in the retentate, in the should be easier to process than traditional whey. Some liquid precheese, and finally in cheese, since drainage of suggested uses of permeate derived from ultrafiltered (UF) whey after coagulating the retentate is completely or nearly milk are given in Table 1. completely eliminated. Thus, of 100 g of nitrogenous sub­ Another benefit claimed for use of UF milk in stances in milk, 94 to 95 g remain in the cheese. This cheesemaking is the reduction in amount of space needed suggests an increase in the yield of cheese from milk of for equipment and handling of cheese. Many cheeses such about 16 to 20%. as Mozzarella, Cheddar, Havarti, cottage, brick, Colby and (b) Composition: After suitable adjustment of the com­ cheese base have been produced either commercially or position of precheese (milk fat, total solids), the resulting experimentally from milk retentate (7,12,18,43,58). cheese will contain the quantities of dry matter and milk fat needed to comply with existing regulations. The safety COMPOSITION AND CHARACTERISTICS OF RETEN­ margin (weight of curd/mold) the cheese maker must allow, TATE DERIVED FROM ULTRAFILTERED MILK as compared to use of the traditional technique, is consid­ erably reduced, and this suggests an important saving of Milk fat raw material. This is particularly true for soft types of Milk fat is entirely retained in the concentrate pro­ cheese such as Camembert. duced by the ultrafiltration membrane. Some of the in­ (c) Rennet or other coagulant used: Because there is crease in yield of cheese made from UF milk results from essentially no drainage of whey, virtually all the coagulant greater retention of fat in curd than in curd made from added to liquid precheese remains in the cheese. Thus, unfiltered milk. This is particularly true for cheeses which traditionally are made with a homogenization step, such as blue cheese, since homogenized milk fat cannot be easily TABLE 1. Suggested uses for permeate from ultrafiltered skim recovered (40). Partial homogenization of milk fat globules milk of whey". in retentate is reported to result from mechanical action and Use Product Processing required not the concentration process (24, 25). The milk fat content of various retentates is given in Table 2. Human food Glucose/galactose syrup Hydrolysis, deionization Human food Alcohol Fermentation Protein Human food Lactose Crystallization Almost all protein of milk appears in the retentate (57). Human food Lactic acid Fermentation The protein content of the retentate also increases as the Human food Antibiotics (Bacteriocins) Fermentation Animal feed Liquid permeate None concentration factor increases. The extra nitrogenous mate­ Animal feed Cattle lick Evaporation, rials retained in cheese made from milk concentrated more crystallization than twofold are as follows: (a) major whey proteins, e.g., Animal feed Powder Drying (3-lactoglobulin and a-lactalbumin, constitute about 60% of Animal feed Lactosylurea Reaction with urea extra nitrogenous material; and (b) the remainder which Animal feed Ammonium lactate Fermentation consists of blood serum albumin, immunoglobulins and Animal feed Biomass Fermentation proteose-peptone. In addition, the glycomacropeptide from Industrial fuel Methane Fermentation K-casein that is normally lost in whey and some unchanged "Adapted from reference (13). K-casein also will be present in cheese made from UF milk

JOURNAL OF FOOD PROTECT/ON, VOL. 54, OCTOBER 1991 ULTRAFILTRATION AND REVERSE OSMOSIS 803 TABLE 2. Composition of retentate and permeate from ultrafiltration of whole milk."*

Product and volume Total Nonprotein concentration factor solids (%) Fat (%) Protein (%) N-compounds (%) Lactose (%) Ash (%)

Retentate IX 12.9 3.9 3.1 0.18 4.7 0.77 3X 28.6 12.6 9.8 0.18 4.1 1.3 5X 43.3 21.8 16.1 0.18 3.2 1.9

Permeate IX 5.7 c 0.00 0.18 4.8 0.53 3X 6.1 — 0.06 0.19 5.1 0.53 5X 6.7 — 0.49 0.19 5.2 0.54

"System: tubular membrane, operation at 50°C. bAdapted from reference (13). cNo data. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021

(40). Whey proteins increase the water-binding capacity of membrane since all the milk fat is retained. Of the water- cheese. The content of nitrogenous materials in various soluble vitamins, folic acid and B12 are bound to protein retentates and permeates is given in Table 2. and so are completely retained by the ultrafiltration mem­ brane (22). Ascorbic acid is rapidly destroyed during ultra­ Minerals filtration probably because air is incorporated during the Calcium in milk exists in two forms: free ions and process (25). However, even under the best of conditions partly bound to casein, phosphate, and citrate. The free ions milk and milk products are not good sources of dietary in the aqueous phase of milk are not concentrated by the ascorbic acid. ultrafiltration membrane. However, calcium bound to ca­ sein micelles increases in retentate as the concentration Viscosity factor increases. Consequently, the buffer capacity of re­ tentate is greater than that of regular milk mainly because The viscosity of retentate increases markedly when the of the higher protein concentration in milk concentrated by protein content exceeds about 14%, with a corresponding ultrafiltration (65). Lactic acid fermentation of milk during decrease in flux (permeation rate) (41). Since the main ultrafiltration and addition of sodium chloride to the reten­ contributor to viscosity is casein, viscosity of retentate can tate followed by diafiltration were reported to decrease the be reduced by treatments which lower the solubility of buffer capacity of retentate (6,54). Diafiltration is a modi­ casein (addition of sodium chloride or citrate) or decrease fication of ultrafiltration in which water is added to the feed the pH of milk before ultrafiltration. It is difficult to as filtration proceeds to wash out feed components which uniformly mix coagulant and starter culture into the reten­ will pass through the membrane. tate if it is very viscous, and this may lead to textural problems in cheese (38). Acidification of the concentrate to Lactose pH 6.0 results in a significant decrease in viscosity (39). At The retention coefficient of lactose was reported to be pH values lower than 5.7, however, there is an increase in 10% although it is assumed that almost all lactose pen­ viscosity caused by increased casein aggregation (38). etrates the ultrafiltration membrane (22). Insufficient re­ Another problem associated with a viscous retentate is moval of lactose during concentration causes textural de­ entrapment of air. It is important to prevent incorporation fects and excessive acid production in cheese during ripen­ of air since its inclusion leads to a spongy-type texture of ing if the retentate is used to make cheese. Consequently, cheese (75). the correct residual lactose level in cheese curd must be obtained (77). The lactose content of retentate can be Texture reduced by diafiltration and pH adjustment; however, there Green et al. (24) reported that a homogenized concen­ is disagreement about the relationship between pH and trate results in a coagulum with a less coarse protein lactose content of the retentate. Qvist et al. (59) reported network which retains more moisture and milk fat, and the pH of milk at ultrafiltration had no significant effect on which gives cheese with fewer textural abnormalities than lactose level in the retentate. In contrast, Sutherland and does nonhomogenized concentrate. Green et al. (25) also Jameson (66) noted a pH-dependent lactose rejection dur­ observed that syneresis by curd made from UF milk tends ing ultrafiltration at lactose concentrations of greater than to be slower than by curd from unfiltered milk. The curd 2.2% in retentate. The lactose content of various permeates obtained from UF milk is relatively difficult to cut, stir, and and retentates is given in Table 2. transport by conventional methods. Consequently, use of special equipment, such as a coagulator (a device wherein Vitamins UF milk is coagulated), is necessary when cheese is to be Fat-soluble vitamins are retained by the ultrafiltration made from UF milk.

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 804 EL-GAZZAR AND MARTH STARTER ACTIVITY IN ULTRAFILTERED MILK levels. Their results suggest that UF skim milk was superior to reconstituted skim milk as a substrate for lactic acid Ultrafiltration increases the content of protein in UF bacteria and hence can be used as a medium for starter milk over that in unfiltered milk and hence its buffering cultures. Also, permeate from Cheddar cheese whey was capacity is increased (6,13). As a result, the amount of used successfully as a medium for propagating several lactic acid that starter culture bacteria must produce to strains of mesophilic lactic acid streptococci (70). cause a unit change in pH is increased considerably over that needed when unfiltered milk is used (49,52). Thus, the BEHAVIOR OF PATHOGENIC BACTERIA IN ripening time of UF cheese milk is lengthened over that of ULTRAFILTERED MILK unfiltered milk. The greater the degree of concentration, the more pronounced will be this increase in buffering As use of ultrafiltration in the dairy industry increases, capacity (52). Even though UF milk is a better growth the industry must be prepared to deal with the possibility medium for lactic acid bacteria than is unfiltered milk that pathogenic microorganisms might appear in UF milk. (29,52), the high buffering capacity of UF milk requires Conditions for growth as well as inhibition of such bacteria production of larger amounts of lactic acid by starter in UF milk differ from those of regular milk (36). Foodborne bacteria than does unfiltered milk. Mistry et al. (53) indi­ pathogens could enter UF milk either from an inadequately Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 cated that addition of 0.5% yeast extract or a mixture of 22 cleaned and sanitized ultrafiltration device or from the amino acids, each at 0.04 mg/g, to retentate from milk environment of the dairy factory. concentrated 2:1 improved acid production as compared to Haggerty and Potter (27) investigated growth/survival the control. of selected pathogenic and/or spoilage microorganisms in Growth and acid production by Streptococcus cremoris UF milk. Studies were made to compare the growth and BKS (Lactococcus lactis ssp. cremoris), in the presence or death of Staphylococcus aureus, Streptococcus faecalis and absence of pH control, increased directly with the concen­ Escherichia coli in milk concentrated by ultrafiltration to tration of UF milk (retentate). Other strains of S. cremoris those in unconcentrated skim milk. Skim milk was volume- and Streptococcus lactis (Lactococcus lactis ssp. lactis) concentrated twofold. Behavior of the organisms was ana­ also produced more lactic acid in retentate than in unfiltered lyzed using four inoculated samples: retentate from twofold milk. Hence, the results suggest that retentate is an im­ concentration, retentate from twofold concentration diluted proved growth medium for starter organisms (29). Reten­ with an equal amount of water, milk equivalent (retentate tate starters (starter prepared in retentate) eliminate the plus permeate) and unfiltered milk. They reported that need for milk ripening, thereby reducing the total growth of each organism was equivalent in the four milk cheesemaking time (time from inoculation of milk with samples at either 7 or 13°C. For S. faecalis and E. coli, D- starter to milling of curd). This is particularly beneficial values at 62.7°C did not differ significantly (P>0.01) when when cheese is made from UF milk, as such milk normally the four types of milk samples served as menstrua. The D- requires longer than unfiltered milk to attain the optimum value of S. aureus heated in water-diluted retentate was pH (49). slightly but not significantly lower than D-values for the Hoier (57) obtained a pH of 4.63 with a culture bacterium heated in the other three types of milk samples, and a pH of 4.04 with Lactobacillus helveticus in an possibly because of the lowered lactose level in the first unspecified time at 40°C in retentate containing 14% pro­ sample. Grieme and Barbano (26) found that the D-value tein (57). Growth of starter organisms was unaffected by for S. aureus MF31 was significantly greater when heated the high content of total solids or ash in retentates. The in whole milk retentates concentrated 1.35-fold by reverse growth rate and lactose metabolism of lactic acid bacteria osmosis than when heated in unconcentrated whole milk, decreased markedly below pH 5.2 at which point the but was not significantly greater when the retentate was population was 109 CFU/ml (57). concentrated by ultrafiltration. Acid production and its relation to pH changes by Rash and Kosikowski (61) characterized survival and commercial direct-set frozen concentrated lactic starters in growth of enteropathogenic E. coli serotype 0124 in skim milk and in retentates from skim milk concentrated Camembert cheese made from retentate of UF skim milk. 2:1 were studied by Mistry and Kosikowski (50). They They reported that differences observed in the physico- indicated that retentates resisted a change in pH below 5.2 chemical properties between conventional and UF cheese despite production of large amounts of lactic acid by starter milk mixtures predisposed Camembert cheeses made from bacteria. Control skim milk required 6 h at 32°C to attain UF milk to greater survival and growth of E. coli than in a pH of 4.6, whereas retentates incubated similarly could similar cheeses made conventionally. not be fermented to this pH even after 8.5 h. Doubling the Evidence in the literature suggests that thermal resis­ starter inoculum in the retentate led to a pH of 4.6 in 7.5 h. tance of some bacteria in UF milk retentates might be Direct-set starter DS1, with more bacteria than direct-set greater than in unfiltered milk. Kornacki and Marth (37) starter DS2, fermented skim milk and UF skim milk reten­ studied the influence of retentates from UF skim on tate (2:1) more rapidly (50). heat resistance of S. aureus. They found nonsignificant Christopherson and Zottola (9) studied growth and (P>0.05) differences in data obtained with unfiltered skim activity of mesophilic starter culture bacteria at their opti­ milk and retentate from skim milk concentrated twofold. mal growth temperature (30°C) in retentate from UF skim However, the difference in data obtained with unfiltered milk and in reconstituted skim milk of similar total solids skim milk and retentate from skim milk concentrated four-

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 ULTRAFILTRATION AND REVERSE OSMOSIS 805 fold was significant (P<0.05). Dega et al. (16) showed that approach the properties of traditional Feta, a bleaching heat resistance of several strains of Salmonella and E. coli agent is usually added to minimize the yellow color of increased as the solids content of reconstituted skim milk cow's milk and lipase is added to promote lipolysis in the was increased from 10 to 50%. cheese. Recently El-Gazzar et al. (17) investigated growth of Olson and Qvist (56) also indicated that Cast Feta Listeria monocytogenes in pasteurized skim milk and in cheese made from UF milk became a great industrial retentate and permeate from UF skim milk. They found success in Greece even though it is significantly different that both strains of L. monocytogenes (V7 and California) from the traditional cheese. Cast Feta cheese has 3 to 4% tested grew faster and achieved higher (ca. one to two more moisture, a smoother texture, and lacks mechanical orders of magnitude) populations at 4°C in retentate from openings of the sort found in traditional Feta cheese. skim milk concentrated twofold or fourfold than in skim Apparently, the most important quality characteristic of milk. The pathogen grew in permeate at 4°C and attained Feta cheese for the consumer in the Middle East is a strong maximum populations of ca. 106 to 107/ml. Tyndallized acid, rancid and salty flavor. This desire is adequately samples of skim milk and of retentate and permeate from fulfilled by the Cast Feta.

UF skim milk were inoculated with the same strains of L. The casting process is technically interesting. The Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 monocytogenes and incubated at 32 or 40°C. Populations, mixture of retentate, lipase, decolorant, starter, and rennet ca. 107 to 107ml, achieved by the pathogen at these tem­ is filled directly into tins with a capacity of 16-20 kg. peratures, were similar in skim milk, retentate, and perme­ Automatic filling occurs in three or four steps, thus one- ate. third or one-fourth of the final amount of retentate is filled into the tin at a time. Between fillings, the tin and its ULTRAFILTERED MILK FOR MAKING CHEESE AND contents are automatically transferred to a holding con­ OTHER DAIRY FOODS veyer belt where solidification of the retentate occurs. When the coagulum is sufficiently firm, the tin is returned Cottage cheese to the filling station and a new layer of retentate is added. Geilman (21) reported that cottage cheese of commer­ Contrary to what might be expected, the layers of cheese do cial quality can be made from UF skim milk retentate not stick together, thus separate layers of cheese are pro­ containing 14.5% solids. To do so, however, trisodium duced. After solidification of the top layer, the cheese is cut citrate had to be added at a rate of 0.3% of the total weight automatically by one or two vertical knives and sodium of retentate to develop a soft coagulum. A pH close to the chloride is added, either as a brine solution or as crystalline normal isoelectric point of casein is satisfactory; the time salt. The tins are then closed and stored at approximately needed for required acid production by the lactic starter 25°C for 1-3 d to ensure that the pH decreases to less than culture depended on the amount of starter bacteria in the 4.8. Some whey will be extracted from the cheese during retentate. Kealey and Kosikowski (35) indicated that UF this period and during subsequent storage at 4°C. To skim milk retentates of 10-fold concentration were pro­ expedite distribution of salt throughout the cheese, tins are duced by a series of direct ultrafiltration and diafiltration normally turned several times during the first 2 weeks of steps. Availability of surplus UF skim milk retentates for storage (56). shipment to cheese factories to supplement skim milk for cottage cheese making thus becomes a distinct possibility. Domiati cheese Retentate-supplemented skim milk yielded commercial cot­ The principal characteristic of Domiati cheesemaking tage cheese of a quality comparable to cheese made from is addition of salt to milk before rennet coagulation occurs, unsupplemented control skim milks. Ricotta and are or before the pH has been reduced. The texture of the other varieties of cheese that are not ripened and thus it resulting coagulum is substantially different from that of should be possible to make them from concentrated milk Cast Feta made from UF milk. If all the salt is added before (41). Matthews et al. (43) demonstrated that ultrafiltration rennet, a soft and pudding-like texture is obtained. Normal can be used as a preconcentration step for continuous lactic acid bacteria, however, will not be active, and so cottage cheese production. glucono-delta-lactone (GDL) is used to reduce the pH. After mixing lipase, decolorant, GDL and rennet into the Feta cheese retentate, it is filled into packaging material used for liquid Olson and Qvist (56) reported that Feta cheese was milk products, e.g., gable-top . Hence, a simple and manufactured from pasteurized (72-78°C/15 s) retentate reliable processing scheme is realized. Considerable quan­ from UF whole milk. Active starters, usually consisting of tities of cheese have been produced in Denmark using this various strains of S. lactis, were used for fermentation. In technology (56). Feta cheese making, it is essential that the minimum pH is Abd-El-Salam et al. (2) made Domiati cheese using UF not higher than 4.8 to prevent softening of the cheese buffalo skim milk (concentration factor of 3.5) mixed with during storage. Sometimes L. helveticus or a yogurt culture fresh cream (about 35% milk fat) at the rate of 4:1. They is used as an adjunct starter to aid in reducing the pH. concluded that Domiati cheese could be satisfactorily made In Greece and the Middle East, traditional Feta is from UF buffalo milk and that storage of cheese without usually made wholly or partly from sheep's or 's milk. pickle (salt brine) caused less weight loss than occurred Feta made from cow's milk is more yellow and less rancid when cheeses were stored in 5% brine solution or in salted than cheese made from the traditional kinds of milk. To (5%) permeate.

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 806 EL-GAZZAR AND MARTH Camembert cheese be made. Skim milk is acidified with acetic acid to pH 6.0, To make Camembert-type cheese, pasteurized skim to remove calcium. This acidified skim milk is pumped at milk initially was concentrated about fivefold by ultrafiltra­ 54°C through a series of ultrafiltration and diafiltration tion. A 20% increase in yield of cheese was claimed when units. Retentate exits in a continuous flow and is blended such retentate was used (33). Maubois (44) described a with plastic cream to make precheese of approximately method for making Camembert cheese using ultrafiltration. 20% milk fat and 28% protein. The precheese is automati­ With the use of concentrated milk and elimination of nearly cally inoculated with a thermophilic lactic starter culture all whey drainage, the size of operation is reduced and and coagulant is added just before it enters a coagulating cheesemaking can be completed in less than the usual time unit where it is dispensed into large metal forms. Coagula­ (22). It has been established in France that Camembert tion occurs in the forms as they move slowly through a cheese can be produced satisfactorily from retentate at the chamber held at about 37 to 43°C. Continued slow move­ rate of 10 tons of cheese in 8 h (28). Jepsen (34) also ment for about 5 h permits a lactic acid fermentation of the indicated that Camembert cheese can be manufactured retentate which results in a pH of 5.2. The acid curd is from UF milk. removed from the forms, reduced in size, and transported to

By using this technology the whey disposal problem is a conventional Mozzarella cheese mixer and molder. Here, Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 reduced. An increase in yield of 11-15% results and use of the curd is heated, stretched, molded, and then immersed in coagulant and starter culture is reduced by 80%. Also, a brine solution. ultrafiltration decreases the amount of milk that must be processed to obtain a given amount of cheese. Thus, either Colby and brick cheeses the size of equipment can be reduced or more cheese can Bush et al. (7) reported that skim milk was fractionated be produced if the size of equipment is not reduced. to attain a 50% volume-reduction by ultrafiltration, stan­ dardized with cream, and used to make brick and Colby Blue cheese cheeses. Reduction in the amount of milk-clotting enzyme Mahaut and Maubois (42) described the manufacture used and elimination of curd washing were achieved. The of blue cheese from UF milk. Cheeses made from retentate experimental brick cheese was more firm and mealy than containing less than 12% protein were as good as, or better the control. It had a more acid flavor, less typical cheese than traditional cheeses. Pichaicharnarong (57) determined flavor, and ranked lower in overall preference than did whether blue cheese made from UF milk had acceptable cheese made from regular milk. Characteristics of Colby properties and also selected a suitable strain (PA, PJ, and cheese made from UF milk were reasonably close to those PV) of Penicillium roqueforti for making blue cheese. of commercial cheeses. The undesirable physical character­ Results indicated that the whey proteins in blue cheese istics that were noted probably could be improved by made from retentate did not suppress proteolytic and lipo­ appropriate choice of milk-clotting and proteolytic en­ lytic activities of P. roqueforti when compared to such zymes. activities in conventional cheese. Strain PV had the highest proteolytic and strain PJ the highest lipolytic activity. Cheddar cheese However, off-flavors occurred in all the blue cheeses made Rao and Renner (60) studied application of ultrafiltra­ from retentate, perhaps because of the interaction of flavor tion to the making of Cheddar cheese. They prepared three compounds with immunoglobulin and proteose-peptone (42). types of Cheddar cheese (45% fat in dry matter): (a) from unfiltered milk according to the traditional procedure, (b) Mozzarella cheese from unheated retentate of UF whole milk, and (c) from Nilson (55) listed the U.S. Federal standards for Moz­ retentate heated at 76°C for 5 min. These cheeses were zarella cheeses, which are as follows: ripened at 13 + 2°C for up to 4 months. The authors found Moisture Fat in the extent of proteolysis (determined by the content of dry matter (%) water soluble nitrogen, nonprotein nitrogen, and nitrogen soluble at pH 4.6 and by changes in the concentration of Mozzarella >52-<60 >45 casein fractions) was highest in cheese made from unfiltered Low moisture Mozzarella >45-<52 >45 milk, followed by cheese made from unheated retentate and Part skim milk Mozzarella >52-<60 >30-<45 lowest in the cheese made from heated retentate. Similar Low moisture, part >45-<52 >30-<45 skim milk Mozzarella differences were observed for extent of lipolysis, deter­ mined by the content of acids in cheeses. Organoleptically, Of the various types, low moisture, part skim milk there was no significant difference in appearance and con­ Mozzarella is the most popular. It has been reported that sistency among the ripened cheese samples. Cheese made Mozzarella cheese which melts satisfactorily can be manu­ from unheated retentate had a slight acidic and bitter flavor, factured from milk concentrated two to fivefold (19,20). but samples prepared from heated retentate scored the same There also are reports that indicate Mozzarella cheese can as did Cheddar cheese made from unfiltered milk. be manufactured from retentate of UF milk and the cheese Sharma et al. (63) made Cheddar cheese from milk develops all the characteristics of cheese made from regular concentrated twofold by ultrafiltration. Lowering the cook­ milk (12,46). ing and cheddaring temperature from 39 to 35°C resulted in Kosikowski (38) described how MMV (Maubois, faster acid development, promoted more proteolysis, caused Mocquot, and Vassal) low moisture Mozzarella cheese can faster disappearance of lactose, and contributed a smoother

JOURNAL OF FOOD PROTECT/ON, VOL. 54, OCTOBER 1991 ULTRAFILTRATION AND REVERSE OSMOSIS 807 body and texture to cheese. Use of starter culture at 2% by The higher mineral content of retentate from UF milk than weight of unconcentrated milk together with lowering the that of unfiltered milk leads to an acid taste and sandy cooking and cheddaring temperature caused the pH to be texture in cheese. Acid and bitter flavors also can arise reduced at a faster rate and shortened the cheese making from excessive lactose in the precheese. Also, behavior of time by approximately 45 min, compared to cheese made lactic acid bacteria and pathogenic microorganisms differ using the traditional temperature (39°C). Composition in retentate from UF milk compared to unfiltered milk. (milk fat, protein, salt and moisture) and yield of cheeses Hence, before UF milk can be used more widely in the made from retentate and using modified temperature treat­ dairy industry additional work needs to be done to solve ments were not significantly different from those of the these problems. Also, economic studies need to be done on control. Nutritional analysis of Cheddar cheese indicates no commercial-scale cheesemaking. More work needs to be noticeable difference in nutrient content of cheese made done on how cheesemaking procedures can be modified so from retentate from UF milk compared to cheese made UF milk can be used to produce satisfactory products. from unfiltered milk (Table 3) (68). Furthermore, regulatory concerns that cheeses made from UF milk may not meet current standards of identity must be

OTHER DAIRY FOODS MADE FROM resolved. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 ULTRAFILTERED MILK REVERSE OSMOSIS: INTRODUCTION Glover (22) indicated that other products such as AND DEFINITION koumiss, ymer, yogurt, and sweetened can be made using UF milk. It has been reported that sandiness The word osmosis is derived from the Greek osmos in sweetened condensed milk was avoided by using ultra­ meaning push (22). The reverse osmosis membrane is filtration (62). permeable to solvents but not to the larger molecules in solution. The osmotic pressure of the solution is directly CONCLUSION: ULTRAFILTERED MILK proportional to the concentration of solute and temperature, and inversely proportional to the molecular weight of the From the foregone, it is evident that use of UF milk is solute. Because the osmotic pressure is inversely propor­ well established for making soft cheese such as Feta, Cast tional to the molecular weight of the solute, small molecu­ Feta, and Domiati since these cheeses can be consumed lar components make a greater contribution to osmotic without ripening. However, when types of cheese that pressure than large ones. Hence, in milk the osmotic pres­ require ripening are made using retentate from UF milk, sure results from salts and lactose rather than proteins. problems develop in their sensory properties because of the It is thought by some that the solvent dissolves in the high content of whey proteins in such cheeses compared to membrane and then passes through by diffusion. The solute traditional cheese. It has been reported that a significantly does not dissolve in the membrane and is therefore held slower degradation of casein occurs, and thus cheese from back; thus the membrane does not need to have pores. UF milk ripens more slowly than traditional cheese (56). Another theory suggests that the membrane has pores and that the solvent molecules being small pass through. Of TABLE 3. Nutrients in Cheddar cheese made from regular milk these, the most useful is the solution diffusion theory (22). and retentate from ultrafiltered milk.' Applications of reverse osmosis in cheese making and other Cheese from Cheese from dairy foods Assay regular milk UF milk Agbevavi et al. (3) made Cheddar cheese from whole Proximate analysis (%) milk concentrated twofold by reverse osmosis (RO). They reported using 50% less starter culture and 60% less rennet Fat 32.4 30.6 than are needed to make cheese from unconcentrated milk. Protein 25.0 25.3 The composition of cheese made from RO-concentrated Lactose <0.5 <0.5 milk was close to that of cheese made from regular milk. Ash 3.4 3.8 They also reported that contamination of the milk with Moisture 39.5 39.7 bacteria already present in the RO system caused a high coliform level in the cheese. Minerals and vitamins (mg/lOOg) Bynum and Barbano (8) reported that Cheddar cheese was made in a commercial factory from whole milk con­ Calcium 757.5 788.0 Iron 0.59 0.52 centrated by RO at 5, 10, 15, and 20% reductions in Magnesium 23.8 23.0 volume. Cheese made from the concentrated milk was Phosphorus 415.0 408.0 compared with control cheese; proteolysis was similar for Potassium 95.0 92.0 both types of cheese during the first 3 months of ripening. Sodium 605.0 585.0 Cheese made from milk reduced in volume by 20% using Zinc 4.0 3.3 RO had a significantly greater lactose content than did Thiamine 0.017 0.015 control cheese. Good quality aged Cheddar cheese was Riboflavin 0.34 0.32 made from whole milk concentrated by RO. Barbano and Bynum (4) studied composition and yield of Cheddar cheese 'Adapted from reference (59).

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 808 EL-GAZZAR AND MARTH manufactured from whole milk concentrated by RO. Whole trated milk is likely to be more limited than use of UF milk milk was reduced in volume by 0, 5, 10, 15, and 20% because of membrane problems in the RO system. Specifi­ before Cheddar cheese was made. Milk solids at the various cally/fouling of the membrane in the RO system is greater levels of milk volume reduction were 11.98, 12.88, 13.27, than in the UF system. 14.17, and 15.05%, respectively. Permeates contained only traces of organic matter and would not create a significant ACKNOWLEDGMENTS byproduct handling problem for a cheese factory. Proxi­ mate composition of cheese made from milk concentrated A contribution from the College of Agricultural and Life Sciences, by RO was comparable to that of control cheese. The University of Wisconsin-Madison. Preparation of this review was sup­ ported, in part, by the Center for Dairy Research at the University of authors (4) also concluded that increased retention of whey Wisconsin-Madison. solids and improved milk fat recovery increased the yield of cheese by 2 to 3% above expected theoretical yields REFERENCES when the reduction in milk volume was 20%. Water re­ moval from whole milk before Cheddar cheese manufac­ 1. Abbot, J., F.A. Glover, D.D. Muir, and P.J. Skudder. 1979. ture gave increased factory productivity and cheese yield Application of reverse osmosis to the manufacture of dried whole Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 without requiring different cheesemaking equipment or milk and skim milk. J. Dairy Res. 46:663-672. manufacturing procedures. 2. Abd-El-Salam, M. H., S. El-Shibiny, N.S. Ahmed, and A.A. Ismail. 1981. Use of ultrafiltration in manufacture of Domiati cheese from Barbano et al. (5) concluded that pressure control buffalo milk. Egyptian J. Dairy Sci. 9:151-157. valves in RO systems for concentrating subpasteurized 3. Agbevavi, T., D. Rouleau, and R. Mayer. 1983. Production and whole milk will cause unacceptable increases in content of quality of Cheddar cheese manufactured from whole milk concen­ trated by reverse osmosis. J. Food Sci. 48:642-643. free fatty acids in milk. Use of a restriction pipe of small 4. Barbano, D.M., and D.G. Bynum. 1984. Whole milk reverse diameter, instead of valves, significantly reduced the amount osmosis retentates for Cheddar cheese manufacture: Cheese compo­ of free fatty acids liberated when subpasteurized whole sition and yield. J. Dairy Sci. 67:2839-2849. milk was concentrated by RO. This approach to pressure 5. Barbano, D.M., D.G. Bynum, and G.F. Senyk. 1982. Influence of regulation may be of significance for on-farm concentration reverse osmosis on milk lipolysis. J. Dairy Sci. 66.2447-2451. 6. Brule, G., J.L. Maubois, and J. Faquant. 1974. Study about the of subpasteurized whole milk or for RO as a milk concen­ mineral elements content in products made from ultrafiltered milk. tration method before making cheese from subpasteurized Le Lail 54:600-615. whole milk. Jensen et al. (32) reviewed composition and 7. Bush, C.S., C.A. Garoutte, C.H. Amundson, and N.F. Olson. 1983. properties of cheeses made from milk concentrated by Manufacture of Colby and brick cheeses from ultrafiltered milk. J. Dairy Sci. 66:415-421. ultrafiltration and RO. They concluded that the final prod­ 8. Bynum, D.G., and D.M. Barbano. 1984. Whole milk reverse ucts were comparable to controls of similar age for most osmosis retentates for Cheddar cheese manufacture: Chemical changes varieties of cheese. However, one of the limitations of RO during aging. J. Dairy Sci. 68:1-10. of skim or whole milk has been membrane fouling 9. Christopherson, A.T., and E.A. Zottola. 1988. Growth and activity of mesophilic lactic acid streptococci in ultrafiltered skim (23,30,64). Membrane fouling refers to irreversible deposi­ milk and in reconstituted nonfat dry milk of differing total solids tion of milk solids on the membrane during processing. content. J. Dairy Sci. 72:2856-2861. 10. Christopherson, A.T., and E.A. Zottola. 1989. The use of whey permeates as starter media in cheese production. J. Dairy Sci. Reverse osmosis and other dairy foods 72:2862-2868. Glover (22) reported that the main application of re­ 11. Covacevich, H.R. 1981. Recent experiences in pasta filata cheese- verse osmosis in dairying is concentration of whey to making by ultrafiltration, pp. 237-244. In 2nd Biennial Marschall facilitate its handling, transport, storage, and to serve as a International Cheese Conference, Madison, Wl. 12. Covacevich, H.R., and F.V. Kosikowski. 1978. Mozzarella and first step in drying. Reverse osmosis for preconcentration Cheddar cheese manufacture by ultrafiltration principles. ]. Dairy' has been suggested for the following products: (a) whey Sci. 61:701-709. powder, (b) whey protein powder, (c) demineralized whey 13. Covacevich, H.R., and F.V. Kosikowski. 1979. Buffer, lactic fer­ powder, and (d) whey-based animal feed. The same author mentation, and rennet coagulation properties of skim milk retentates produced by ultrafiltration. J. Dairy Sci. 62:204-207. (22) indicated that made with RO concentrates 14. Davies, F.L., P.A. Shankar, and H.M. Underwood. 1977. The was as good as that made with traditional ingredients. use of milk concentrated by reverse osmosis for the manufacture of Davis et al. (14) compared yogurt made from milk yogurt. J. Soc. Dairy Technol. 30:23-28. concentrated by RO to 15% total solids with that made 15. de Boer, R., and P.F.C. Nooy. 1980. Low-fat semi-hard cheese from milk adjusted to comparable concentrations of solids from ultrafiltered milk. North Eur. Dairy J. 46:52-61. 16. Dega, C.A., J.M. Goepfert, and C.H. Amundson. 1972. Heat resis­ by addition of skim milk powder. The quality of yogurt tance of salmonellae in concentrated milk. Appl. Microbiol. 23:415- prepared from the RO concentrates was at least equal to 420. that of yogurt prepared from the milk plus milk powder. 17. El-Gazzar, F.E., H.F. Bohner, and E.H. Marth. 1991. Growth of Abbot et al. (7) found no significant differences in proper­ Listeria monocytogenes at 4, 32 and 40°C in skim milk and in retentate and permeate from ultrafiltered skim milk. J. Food Prot. ties of milk powders made from milk concentrated initially 54:338-342. by RO compared to those prepared in the traditional way. 18. Ernstrom, C.A., B.J. Sutherland, and G.W. Jameson. 1980. Cheese base for processing. A high yield product from whole milk by Conclusion: Reverse osmosis ultrafiltration. J. Dairy Sci. 63:228-234. 19. Fernandez, A., and F.V. Kosikowski. 1986. Physical properties of In conclusion, it is evident that much work needs to be direct acidified Mozzarella cheese from ultrafiltered whole milk done before RO concentrated milk can be used more retentates. J. Dairy Sci. 69:643-648. widely in the dairy industry. However, use of RO concen­ 20. Fernandez, A., and F.V. Kosikowski. 1986. Low moisture Mozza-

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991 ULTRAFILTRATION AND REVERSE OSMOSIS 809

rella cheese from whole milk retentate of ultrafiltration. J. Dairy Sci. num Press, New York. 69:2011-2017. 45. Maubois, J.L., and G. Moquot. 1974. Application of membrane 21. Geilman, G.W. 1989. Use of UF retentate for cottage cheese ultrafiltration to preparation of various types of cheese. J. Dairy Sci. manufacture. In Symposium on advances in dairy products technol­ 58:1001-1007. ogy. San Luis Obispo, CA, Oct. 4-5. 46. Maubois, J.L., and F.V. Kosikowski. 1978. Preparation of Mozza- 22. Glover, F.A. 1985. Ultrafiltration and reverse osmosis for the dairy rella cheese by membrane ultrafiltration. Proc. 20th Int. Dairy Congr., industry. National Institute for Research in Dairying, Reading, En­ vol. E:792-793. gland. 47. Maubois, J.L., G. Mocquot, and L. Vassal. 1969. A method for 23. Glover, F.A., and B.E. Booker. 1973. The structure of the deposit processing milk and dairy products. French Patent No. 2,052,121. formed on the membrane during concentration of milk by reverse 48. Maubois, J.L., G. Ricordeau, and G. Mocquot. 1970. A study osmosis. J. Dairy Res. 41:89-93. of the Camembert and Saint-Paulin cheese yields. Lait 50:351-373. 24. Green, M.L., F.A. Glover, and RJ. Marshall. 1982. Cheddar 49. Mistry, V.V., and F.V. Kosikowski. 1985. Growth of lactic starters cheesemaking behavior of whole milk concentrated by ultrafiltration. in milk retentates. J. Dairy Sci. 68:1484-1490. Proc. 21st Int. Dairy Congr., vol. 1, book 2:448. 50. Mistry, V.V., and F.V. Kosikowski. 1985. Fermentation of ultra- 25. Green, M.L., K.J. Scott, M. Anderson, M.C.A. Griffin, and F.A. filtered skim milk retentates with mesophilic lactic cheese starters. Glover. 1984. Chemical characterization of milk concentrated by J. Dairy Sci. 68:1613-1617. ultrafiltration. J. Dairy Res. 51:267-278. 51. Mistry, V.V., and F.V. Kosikowski. 1985. Growth of lactic acid 26. Grieme, L.E., and D.M. Barbano. 1983. Method for use of a bacteria in highly concentrated ultrafiltered skim milk retentates. J.

differential scanning calorimeter for determination of bacterial ther­ Dairy Sci. 68:2536-2543. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/54/10/801/1661973/0362-028x-54_10_801.pdf by guest on 24 September 2021 mal death times. J. Food Prot. 46:797-801. 52. Mistry, V.V., and F.V. Kosikowski. 1986. A naturally buffered bulk 27. Haggerty, P., and N. Potter. 1986. Growth and death of selected retentate starter from ultrafiltered milk. J. Dairy Sci. 69:945-950. microorganisms in ultrafiltered milk. J. Food Prot. 49:233-235. 53. Mistry, V.V., F.V. Kosikowski, and W.D. Bellamy. 1987. Improve­ 28. Hansen, R. 1981. UF-Camembert manufactured on the new ment of lactic acid production in ultrafiltered milk by the addition of CAMATIC. North Eur. Dairy J. 47:147-152. nutrients. J. Dairy Sci. 70:2220-2225. 29. Hickey, M.W., H. Roginski, and M.C. Broome. 1983. Growth and 54. Mocquot, G. 1979. Present potential of ultrafiltration in cheesemaking. acid production of group N streptococci in ultrafiltered milk. Aust. p. 603. In Proceedings 1st Biennial Marschall International Cheese J. Dairy Technol. 38:138-143. Conference, Madison, WI. 30. Hiddink, J., R. deBoer, and P.F.C. Nooy. 1980. Reverse osmosis 55. Nilson, K.M. 1989. Evaluation criteria for Italian cheesemakers in of dairy liquids. J. Dairy Sci. 63:204-214. the adoption of membrane processing technology. In Symposium on 31. Hoier, E. 1984. Use of rennet and starter cultures in ultrafiltered advances in dairy products technology. San Luis Obispo, CA, Oct. concentrates. Dtsch. Milchwirtsch. 13:443-450. 4 - 5 . 32. Jensen, L.A., M.E. Johnson, and N.F. Olson. 1987. Compo­ 56. Olson, N.F., and K.B. Qvist. 1989. Manufacture of soft and semi- sition and properties of cheeses from milk concentrated by ultrafil­ soft cheeses utilizing ultrafiltration. In Symposium on advances in tration and reverse osmosis. A review of literature. Cult. Dairy dairy products technology. San Luis Obispo, CA, Oct. 4 - 5 . Prod. J. 22(2):6-14. 57. Pichaichamarong, S. 1990. Effects of Penicillium roqueforti strains 33. Jepsen, S. 1975. Production of Camembert cheese by ultrafiltration on blue cheese made from ultrafiltered milk. M. S . Thesis, Univer­ according to the MMV Process. North Eur. Dairy J. 41:101-105. sity of Wisconsin, Madison, WI. 34. Jepsen, S. 1977. The manufacture of cultured milk products: yogurt, 58. Qvist, K.B., D. Thomsen, and G.K. Jensen. 1986. Manufacture of ymcr, Camembert cheese. Cult. Dairy Prod. J. 12(3): 14-17. Havarti cheese from milk concentrated ca. 5-fold using ultrafiltra­ 35. Kealey, K.S., and F.V. Kosikowski. 1985. Cottage cheese from tion. Beretningfra Statens Mejeriforsog No. 268. Denmark. ultrafiltered skim milk retentates in industrial cheesemaking. J. Dairy 59. Qvist, K.B., D. Thomsen, and E. Hoier. 1987. Effect of ultrafiltered Sci. 69:1479-1483. milk and use of different starters on the manufacture, fermentation, 36. Kerrigan, G.L. 1989. Methods to evaluate the economics of mem­ and ripening of Havarti cheese. J. Dairy Res. 54:437-446. brane separation processes for cheese manufacture. In Symposium 60. Rao, D.V., and E. Renner. 1989. Studies on the application of on advances in dairy products technology. San Luis Obispo, CA, ultrafiltration for the manufacture of Cheddar cheese. 3. Ripening Oct. 4-5. characteristics. Milchwissenschaft 44:351-354. 37. Komacki, J.L., and E.H. Marth. 1989. Thermal inactivation of 61. Rash, K.E., and F.V. Kosikowski. 1982. Behavior of entero- Staphylococcus aureus in retentate from ultrafiltered milk. J. Food pathogenic Escherichia coli in Camembert cheese made from Prot. 52:631-637. ultrafiltered milk. J. Food Sci. 47:728-732, 736. 38. Kosikowski, F. 1986. New cheesemaking procedures utilizing ultra­ 62. Serpa, A.D., M. Bennasar, and B. Tarodo. 1979. Application of filtration. Food Technol. 40(6):71-77. ultrafiltration to the manufacture of sweetened condensed milk. Lait 39. Kristensen, A.S., W.K. Nielsen, and R.F. Madsen. 1981. New 59:376-386. DDS-ultrafiltration module for high concentration of milk products 63. Sharma, S.K., L. K. Ferrier, and A.R. Hill. 1989. Effect of in connection with production of cheese. North Eur. Dairy J. modified manufacturing parameters on the quality of Cheddar cheese 47:268-274. made from ultrafiltered milk. J. Food Sci. 54:573-577. 40. Lawrence, R.C. 1987. The use of ultrafiltration technology in 64. Skudder, P.J., F.A. Glover, and M.L. Green. 1977. An cheesemaking. International Dairy Federation B-Doc. 136, Brussels. examination of the factors affecting the reverse osmosis of milk with 41. Lelievre, J., and R.C. Lawrence. 1988. Manufacture of cheese from special reference to deposit formation. J. Dairy Res. 44:293-307. milk concentrated by ultrafiltration. A review. J. Dairy Res. 55:465- 65. Spangler, P. 1989. The development of manufacturing parameters 478. for Gouda and Havarti cheese manufactured using ultrafiltered milk. 42. Mahaut, M., and J.L. Maubois. 1978. Application of the MMV Ph.D. Thesis, University of Wisconsin, Madison. process to the making of blue cheeses. Proc. 20th Int. Dairy Cong. 66. Sutherland, B.J., and G.W. Jameson. 1981. Composition of hard vol. E:793-794. cheese manufactured by ultrafiltration. Aust. J. Dairy Technol. 43. Matthews, M.E., S.E. So, C.H. Amundson, and C.G. Hill, Jr. 36:136-143. 1976. Cottage cheese from ultrafiltered skim milk. J. Food Sci. 67. Vandewcghe, J., and J.L. Maubois. 1968. Final report. D.G.R.S.T. 41:619-622. Contract No. 6101012, Paris. 44. Maubois, J.L. 1980. Recent development of membrane ultrafiltra­ 68. Zall, R.R. 1984. On-farm ultrafiltration membrane-processing of tion in the dairy industry, pp. 305-318. In A.R. Cooper (ed.), milk on the dairy farm. Final report covering July 84-Oct. 85 for Ultrafiltration membrane and applications (Symposium 1979). Ple­ Dairy Research Incorporated and California Milk Advisory Board.

JOURNAL OF FOOD PROTECTION, VOL. 54, OCTOBER 1991