Incorporation of whey proteins in cheese

International Dairy Journal 11 (2001) 495 503 Incorporation of whey proteins in cheese J. Hinrichs* Institute for Food Technology, Animal Foodstuff Technology, University of Hohenheim, Garbenstr. 54, D-70599 Stuttgart, Germany Abstract In traditional cheese-making casein forms the curd structure while whey proteins are lost in the whey. When whey proteins are integrated into fresh, soft, semi-hard and hard cheese, this not only improves the nutrient value and yield but also causes changes to functional properties. There are several technologies for re-integrating whey proteins into cheese during processing. The application and process adaptations depend mainly on the type of cheese and the desired texture. Whey proteins may be retained by applying high heat treatment in order to affix the whey proteins to caseins or by using membrane technology to reduce the aqueous phase. Alternatively, whey proteins may be removed from drained whey by ultrafiltration and then added to curd after special heat treatment or by recycling into cheese milk. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cheese; Whey protein; Ultrafiltration; Nanofiltration; High heating; Yield 1. Introduction Cheese is a dairy product which has played a key role in human nutrition for centuries. The broad range of different cheeses available is based mainly on regional conditions and production technology, which has been repeatedly adapted and optimized. The main objective has always been and still is to convert milk, which is perishable, into a product with a longer shelf-life whilst preserving its nutrients. In order to preserve a product without thermal treatment and appropriate packaging, it is necessary to lower its water activity (a w -value). Rennet coagulation of milk in combination with fermentation is an effective means of dehydrating the resulting curd that forms at the expense of losing valuable whey proteins. New technologies have enabled the integration of the whey proteins and different milk constituents into the cheese matrix, in order to improve its nutrient value as well as the economic effectiveness of cheese production (e.g. Lawrence, 1989; Pedersen, 1991; Kessler, 1996). In traditional rennet cheese manufacturing only 6 30 kg milk constituents in form of curd is recovered from 100 kg milk depending upon cheese type whilst the remainder is represented by whey. The essential structure of the cheese matrix is formed by the caseins, *Tel.: +49-711-4593792; fax: +49-711-4593443. E-mail address: jh-lth@uni-hohenheim.de (J. Hinrichs). which constitute about 80% of the milk proteins. The remaining 20%, the whey proteins, are lost to a large extent in the whey. In the meantime, different technologies have been tried and tested, and some are now wellestablished to integrate whey proteins into cheese, and thus, improve the use of the raw material, milk. Whey proteins may be incorporated in principle both in a native form and in a denatured state into cheese (Lawrence, 1989, 1993a, b, c). In their native form, they may be retained during processing (Fig. 1) when ultrafiltration membranes are used for the partial or full concentration of the milk. In a denatured form different technologies are available: (1) high heat treatment of the milk in order to affix the whey proteins to the caseins so that they are retained in the cheese matrix; (2) combining high temperature heating and membrane technology to retain the denatured and aggregated whey of the serum phase; (3) recycling thermally modified, particulated whey proteins via protein incorporation into cheese milk or (4) adding these to the cheese matrix (Fig. 1). Yield is of special interest in cheese manufacturing for profitability reasons and may be calculated from Yield ¼ m cheese 100: ð1þ m milk The yield of cheese is influenced by different factors, e.g., it is increased (i) as the fat and protein contents of milk increase; (ii) by retaining or re-incorporating whey proteins, and (iii) by integrating other milk constituents 0958-6946/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0958-6946(01)00071-1

496 J. Hinrichs / International Dairy Journal 11 (2001) 495 503 such as lactose or ash, as well as water. In order to calculate the incorporation of whey proteins from milk into the cheese matrix (yield), the mass of whey proteins in both milk and cheese should be included in Eq. (1). 2. Fresh cheese Fresh cheese is a very popular dairy product in Europe. Fig. 2 shows the individual steps involved in the Fig. 1. Possibilities for the incorporation of native and denatured whey proteins into cheese. production process and the improvements in technology for the incorporation of whey proteins. Using the more traditional method (a), skim milk is HTST (high temperature, short-time heated to 741C for 40 s) treated, fermented and whey separated by a centrifugal separator. The final product is firm and it is possible to achieve a high total solids content. The maximum yield of integrated whey proteins of milk is approx. 15%. In an improved process (b), to obtain what is known as thermoquarg, milk is heated to high temperatures in order to denature whey proteins and induce selfaggregation and interaction with caseins. The amount of integrated whey proteins may be increased to between 50% and 70% depending on the degree of denaturation. Appropriate heating conditions within a range of 82 951C for about 360 80 s ensure that the degree of whey protein denaturation exceeds more than 90% in skim milk (Kessler, 1996). High preheat temperature improves yield, stability of the product and the texture which is smoother than that achieved with process (a) due to increased water binding of the denatured whey proteins. In order to extend whey protein yield in fresh cheese, a retentate produced by means of ultrafiltration of the acid whey (c) is added to the curd. However, if too much retentate is added, a strange whey taste often develops in Fig. 2. Incorporation of whey proteins into fresh cheese processing.

J. Hinrichs / International Dairy Journal 11 (2001) 495 503 497 the final fresh cheese during storage, so the amount of whey added must be limited. Further attempts have been made to retain the whey proteins by introducing ultrafiltration during fresh cheese processing (d) (Pedersen & Ottesen, 1992; Kessler, 1996). This technology allows the integration of all whey proteins, but a bitter taste develops during storage, which is attributed to (i) the high buffering capacity of the retentate, (ii) increased starter growth and proteolytic activity, and (iii) the higher amount of calcium compared with the fresh cheeses produced by the processes (a) (c) (Puhan & Gallmann, 1981). These problems were overcome by exchanging the order of unit operations (B.auerle, Walenta, & Kessler, 1984) so that fermentation takes place first followed by concentration (e). The prior-acidification of milk facilitates the release of casein-bound calcium into the permeate during concentration. High temperature heating (as in b), which is responsible for the well-known smooth and creamy curd structure of the UF fresh cheese compared with thermoquarg (Fig. 3), have helped establish this technology on an industrial scale. Process (f) constitutes yet a further improvement. The milk is pre-concentrated up to a volume concentration ratio (VCR) of 2, which does not alter the fermentation (Schkoda & Kessler, 1996; Schkoda & Kessler, 1997; Schkoda, Stumpf, & Kessler, 1998). Ultrafiltration as well as nanofiltration may be applied for the first concentration step. Up to 100% of the whey proteins of the milk are integrated depending on whether the second step is carried out by separator or ultrafiltration. In addition, the amount of lactose and calcium is increased compared to process (e). Despite the high amount of calcium, a bitter flavor does not develop, which indicates that the proteolytic activity of the starter culture and not the calcium content is the major factor associated with bitter flavor in fresh cheese (Schkoda & Kessler, 1997). Fig. 3. Comparison of the rheological properties of thermoquarg and UF fresh cheese. Fig. 4. Texture profile of samples of thermoquarg, UF fresh cheese and FML fresh cheese at 51C (Schkoda & Kessler, 1996). Rheological properties are also influenced by the process method and the amount of integrated whey proteins and other milk constituents. Fig. 4 shows the differences between thermoquarg, UF fresh cheese and fresh cheese produced by the new FML process (Schkoda & Kessler, 1997). A cylinder penetrates the sample twice and force is shown as a function of the measuring time. In comparison, the curves demonstrate that the thermoquarg structure is firmer than that of the FML fresh cheese and UF fresh cheese. In summary, modifications of process technology in order to improve the integration of valuable whey proteins or other milk constituents are accompanied by textural changes. Thus, it may be necessary to adapt process conditions as well as the starter culture to obtain a high quality product and consumer acceptance. 3. Cheeses produced by UF technology Ultrafiltration technology has meanwhile been established on an industrial scale in modern dairies enabling whey proteins and other milk constituents to be retained in the cheese. Among the examples are fresh cheese, as already shown, fresh cream cheese, soft cheese (i.e. Camembert), Feta cheese, Pasta Filata (i.e. Mozzarella), Cheddar cheese, cheese base, cottage cheese and butter cheese (King, 1986; Hansen, 1987; Rao & Renner, 1988; Hansen, 1989) Ultrafiltration may be integrated into the cheesemaking process either for partial or full concentration. In the latter application, curd cutting and whey drainage are entirely eliminated and 100% of the whey proteins of milk are retained in the cheese matrix. However, this technology may not be applied successfully to produce cheeses with a high total solid content such as semi-hard and hard cheese because the viscosity

498 J. Hinrichs / International Dairy Journal 11 (2001) 495 503 Fig. 5. Permeation flux as a function of the degree of concentration in a tubular UF module (Gernedel & Kessler, 1980 cit. in Kessler (1996)). of the product as well as permeation flux limit the degree of concentration (Fig. 5). At >5 concentration, only 10% of typical skim milk flux is attained due to the high viscosity of the retentate and fouling, which renders ultrafiltration ineffective. Typical and very successful products of this technology are UF soft cheese types, e.g. Camembert and Feta, which are produced from about fivefold concentrated milk. However, one must bear in mind that the changes to the composition and technology influence the texture of the product and adaptations are necessary to produce a high quality cheese. Partial concentration may be applied also in the manufacturing process to produce cheeses with a higher amount of total solids, e.g. SiroCurd process (Radford, Freeman, Jameson, Leeuwen, & Sutherland, 1988) or yellow cast cheese (APV, 1992; Hansen, 1989; Dybing, 1995; Guinee et al., 1995). The milk is concentrated up to a volume concentration ratio of 2 to 3, followed by the customary unit operations of cheese manufacturing with adaptations. As the amount of drained whey is reduced, this technology allows the integration of more whey proteins compared to the traditional method. The higher the volume concentration ratio, the higher the amount of retained whey proteins and fat (Gernedel, 1980). Further efforts to increase yield require that careful attention must be paid to the final product because the texture, ripening and also melting conditions may change. It is necessary to adapt the processing conditions depending on the degree of concentration. When milk is ultrafiltered the fat globules are also recovered in addition to the caseins and whey proteins. This enables the concentration of whole milk and cream Fig. 6. Composition of UF retentate depending on the fat concentration of the milk (adopted from Grimm et al. (1995)). and the standardization of the cheese milk. Fig. 6 shows the limitations (called maximum operation lines) for the combined concentration of protein and fat in homogenized and non-homogenized milk. The technical limitations identified by Grimm, Huss, and Kessler (1995) are a result of the combined effects of viscosity increase and deposit formation, which is in agreement with the experiments carried out by Gernedel (1980). In particular, the viscosity increase induced by homogenization of cream results in a lower limit line for homogenized milk and cream in contrast to the nonhomogenized samples (Fig. 6). An example shall serve to explain the diagram with the objective of being able to produce a cream fresh cheese with 30% fat and 7% protein by means of full concentration (see Fig. 6): according to the fat and protein ratio the starting point is located on the separator operation line at about 15% fat, which represents the composition of the milk upon leaving the centrifugal separator. Therefore, cheese milk requires standardization to 15% fat by the separator before ultrafiltration is applied. The same procedure may be used for other cheese products. Fig. 6 may be useful also for applied situations involving partial concentration (2x23x) as already mentioned. On the one hand, gel strength of the coagulum increases so that processing has to be adapted but whey proteins are still lost in the whey. In fresh cheese technology, high temperature heating of the milk

J. Hinrichs / International Dairy Journal 11 (2001) 495 503 499 may be used to increase whey protein recovery, but the question arises about its applicability to cheese milk intended for semi-hard or hard cheese. Rennet-induced gelation was hindered when more than 60% whey proteins of cheese milk were denatured (Steffl, 1999). In addition, gelation time was prolonged. Therefore, high heat treatment of milk should be ruled out as a possible application for the production of semihard and hard cheese production. Schreiber (2000) studied the limitations of high heating ultrafiltration concentrates on gel formation in order to affix whey proteins to the caseins and increase their retention in the cheese matrix. The inset diagram (Fig. 7) illustrates schematically the effect that blocking of the caseins by denatured whey proteins and casein content have on gel formation and resulting gel strength. The first row demonstrates that ultrafiltration without subsequent heating and denaturation of the whey proteins leads to an increase in casein content and connections in the network with an increase of the F-60- value (defined as the gel strength after 60 min of rennet action). In the next row, caseins are blocked by heatdenatured whey proteins. Rennet-induced aggregation is impeded and reduces the amount of connections in the casein network. The more caseins that are blocked, the lower the F-60-value. But concentration of milk counteracts the reduction in gel strength because more caseins for network formation are available (Maubois, Mocquot, & Vassal, 1975; McMahon, Savello, Brown, & Kalab, 1991; McMahon, Yousif, & Kalab, 1993; Guinee, O Callaghan, Pudja, & O Brien, 1996; Smith & McMahon, 1996; Waungana, Singh, & Bennet, 1996; Schreiber, 2000). In summary, gel strength decreases due to blockage of caseins and increases with milk concentration. A diagonal representing a line of equal gel strength may be imagined corresponding to the counter-effects of Fig. 7. Line of equal effect for rennet-induced gels depending on the casein content and the degree of whey protein denaturation (adopted from Schreiber (2000)). blocking the casein and the concentration of the casein on the network formation (Fig. 7). The relationship between the degree of whey protein denaturation and casein concentration which is necessary to reach the gel strength of pasteurized skim milk is described in Fig. 7. Greater denaturation of milk is permitted when casein content is increased. Furthermore, above a protein concentration of about 8% (VCR about 3), all whey proteins may be denatured because then the gel strength attained is higher than that of skim milk (Schreiber, 2000). This means that high heating and denaturation of whey proteins is possible, in order to integrate them into the cheese, if the milk is concentrated. Pilot-scale tests for semi-hard cheese type Edamer, resulted in an increased yield and the possibility of heating the concentrate in order to inactivate spore formers (Schreiber, 2000) and eliminate the addition of bacteriocides. However, ripening as well as the functional properties may be influenced by high heating of concentrated milk and the altered composition of the resulting cheese (Berg van den & Exterkate, 1993; Guinee et al., 1995; Enright & Kelly, 1999 cit. in Schreiber, 2000; Steffl, 1999). 4. Addition of whey protein particles The incorporation of whey proteins into the matrix of cheese with a high total solids content may be increased by partial concentration of milk, although retention does not reach 100%. Bachmann, Schaub, and Rolle (1975) showed that added denatured whey proteins in cheese milk are mechanically retained in the rennetinduced gel network. The consequences of adding whey protein concentrates in terms of yield and characteristics of different cheeses are illustrated in Table 1. Whey protein addition leads to increased yield but may result in a slightly poorer quality cheese flavor and texture. Improved yield is attributed to both an increased retention of serum in the cheese matrix, and the incorporation of whey proteins. In particular, denatured and highly hydrated whey proteins obstruct syneresis, so that less water drains off during the cheesemaking process (Lucey & Gorry, 1994). By applying the usual technological countermeasures, such as intensified curd working, water content may be reduced with beneficial influences on quality-relevant parameters. Valuable whey proteins are retained preferentially in a denatured and more aggregated (particulated) state in a gel network (Fig. 8). Particulation is a technology by which whey proteins are denatured and aggregated by heating with simultaneous shearing into particles in a whey concentratefthe efficiency depends on composition and the process conditions, e.g. Simpless s (Singer, Yamamoto, & Latella, 1988; Fang, 1991) Dairy-Lo TM

500 J. Hinrichs / International Dairy Journal 11 (2001) 495 503 Table 1 Influence of the addition of whey protein concentrates on the yield and properties of various cheese types (adopted from Steffl, 1999) Cheese type Whey concentrate Added amount (%) Additional yield (%) Flavor Texture Reference Camembert Whey-UF 5, 10 Yes Bitter, Soft, uneven Birkkjaer (1976) (851C, 20 s) atypical ripened Semi-hard cheese Whey UF 5.56 12 Sour Less holes Birkkjaer (1976) (851C, 20 s) Gouda Centri-whey Not given Yes Less Crumbly Berg van den (1979) processt (ph 5) Saint-Paulin Centri-whey 0 10 11 17 Sour, Soft, crumbly Abrahamsen (1979) processt (UF) atypical Hard cheese Centri-whey 0 9 14 Less Less Abrahamsen (1979) (type Emmentaler) processt (UF) Cheddar Whey UF (751C, 30 min) 3.5 4 Sour Soft Brown and Ernstrom (1982) Cheddar centri-whey processt 5 6 12 15 Normal Minimal softer Banks and Muir (1985) (ph 4.5) Cheddar Whey protein 5 10 Max. 7 Atypical Sticky Baldwin et al. (1986) concentrate Gouda Whey protein Not given Yes Acceptable Soft Zoon and Hols (1994) concentrate Red. fat Gouda Simplesse s 2 15 Sour Minimal softer Lucey and Gorry (1994) Semi-hard cheese Whey protein 10 3 Normal Not given Santoro and Faccia (1996) concentrate (901C, 5 min) Cheddar Dairy-Lot 1 Not given Less Less Fenelon (1997) Soft cheese (type Camembert) Whey protein particle 1 Max. 30 Normal Soft Steffl (1999) Fig. 8. Effect of the degree of denaturation of whey protein particles on their retention in soft cheese and semi-hard cheese (adopted from Hinrichs and Steffl (1998)). (Asher, Mollard, Thomson, Maurice, & Caldwell, 1992) or produced by other means (Queguiner, Dumay, Salou- Cavalier, & Cheftel, 1992; Paquin, Lebeuf, Richard, & Kalab, 1993; Huss & Spiegel, 1999; Spiegel, 1999). The effect of degree of denaturation on the retention of whey proteins in soft and semi-hard cheese was studied using two whey protein concentrates (WPC 1 and WPC 2) and a whey protein isolate (WPI) which were heated and shear-treated in order to particulate the whey proteins (Fig. 8). The amount of WPC or WPI added was varied between 0.3% to 1.25% protein. There was a significant increase in retention as a result of increasing degree of denaturation for WPC and WPI. The maximum retention of 70% for semi-hard cheese was achieved for >90% denaturation. During soft cheese production a higher recovery of whey protein is possible, especially when WPI was particulated. Whey protein particles (WPP) are inserted inertly into the pores of the casein network like fat globules (Steffl, 1999), while added undenatured whey proteins as well as native whey proteins of milk are lost in the whey. The pore size of the network is indicated as approx. 10 mm (Walstra & van Vliet, 1986 cit. in Steffl, 1999), which means that this is the critical diameter for added particles. WPP between 1 and 10 mm are integrated inertly into the structure; however, larger particles disturb the homogeneity of the network, and result in a reduction of the firmness (Hinrichs & Steffl, 1998). There is a further advantage of WPP: due to their size and structure they act similarly to integrated fat globules do, so that the quality of cheese, particularly with a low fat content, is improved (Steffl, 1999). However, adjustments in cheese processing must be made when recycling whey proteins in the form of particles in order to lower the water content on the one

J. Hinrichs / International Dairy Journal 11 (2001) 495 503 501 Table 2 Maximum addition of whey protein particles in the FML-process for cheese fortified with whey protein (adopted from Schreiber et al., 1998a; Schreiber et al., 1998b; Steffl, 1999) a Cheese type Addition of particulated WPC b in g protein/100 g milk Integrated whey proteins of milk in % Soft cheese Max. 0.7 g Max. 100 Semi-hard cheese Max. 0.5 g Max. 70 Hard cheese Max. 0.3 g Max. 50 a Max., maximum amount. b Degree of whey protein denaturation of about 90%. Fig. 9. Process modification in cheese manufacture of soft, semi-hard and hard cheese when adding whey protein particles. hand and to remove milk constituents from the cheese on the other hand, which are additionally recycled with WPP such as lactose. The basic steps in the production process of soft, semi-hard and hard cheese-making are shown in Fig. 9. When adding whey protein particles, renneting properties may to be improved by raising fermentation and renneting temperature by 2 31C, as is usually applied for high fat cheeses. Further processing of the cheese curdfwhey removal and addition of washing waterfcontributes to a mild cheese by reducing lactose content. Lactose is also increased when adding whey protein particles produced from WPC which means that washing should be intensified. Additionally, moisture of the cheese increases. Certain measures may be used to reduce water content, e.g. cutting curd into smaller cubes and/or increasing the processing temperature after cutting to improve the syneresis. These adaptations lead to ph-values within a normal range at the end of the ripening phase. Salting time may be reduced depending on moisture content (Schreiber, Neuhauser, Schindler, & Kessler, 1998a; Schreiber, Post, & Kessler, 1998b). There are limits to the adaptations that may be made to the cheese-making process. Therefore, the extent of recycling of whey protein particles is restricted depending, e.g. on the moisture specification of individual cheese types and on the texture. In this manner, high quality cheeses may be produced with fortified whey proteins. The maximum amount of added whey protein particles and the resulting recovery of whey proteins in the cheese matrix is determined by the dry matter content of the cheese (Table 2). The higher the required total solids content, the lower the amount of added WPP and, thus, the lower the integration of whey protein. In order to benefit from whey protein integration and satisfy high quality standards, adaptations of either the particulation process or cheese-making should be carried out. 5. Conclusions In traditional cheese-making, casein forms the curd structure while the whey proteins are lost in the whey. In order to use the nutritionally valuable whey proteins and increase yield several attempts have been made to recover or to re-integrate them into the cheese matrix. Industrial applications and the required adaptations to the cheese-making process depend mainly on the requirements of cheese type and the desired texture. Whey proteins are retained by either applying high temperatures in order to interact with the caseins or recovering by membranes in order to reduce the aqueous phase. Alternatively, whey proteins may be restrained and recovered from drained whey by ultrafiltration so that they may be added after special treatment (i.e. particulation), added to the curd or recycled into the cheese milk. Meanwhile, several advanced processes, depending on the type of cheese, are being established in dairies. The advantages of incorporating whey protein into cheese are higher nutritional value, increased cheese yield and, especially in the case of low fat cheese, sensory improvement. Besides, it puts whey to good use. Furthermore, when fermentation takes place in the retentate, not only the amount of retained whey protein increases, rennet and starter cultures are also saved. But in order to benefit from the incorporation of the whey protein, cheese-making conditions require adaptations to suit the composition of the cheese milk and the requirements of the product in order to produce a high

502 J. Hinrichs / International Dairy Journal 11 (2001) 495 503 quality cheese. The textural changes are not negative and may even present an opportunity to create innovative cheese products with a creamy and soft structure and a high amount of valuable whey proteins. References Abrahamsen, R. K. (1979). Cheesemaking from milk fortified with ultrafiltrated whey protein concentrate. Milchwissenschaft, 34, 65 68. APV (1992). A process and an apparatus for the preparation of cheese. International Patent Application No. PCT/DK92/00163. Asher, Y. J., Mollard, M. A., Thomson, S., Maurice, T. J., & Caldwell, K. B. (1992). Whey protein product: Method for its production and use thereof in foods. International Patent Application WO 92/ 20239. Bachmann, M., Schaub, W., & Rolle, M. (1975). Beitrag zum problem der Molkenverwertung. Schweizerische Milchwirtschaftliche Forschung, 4, 1 8. Baldwin, K. A., Baer, R. J., Parsons, J. G., Seas, S. W., Spurgeon, K. R., & Torrey, G. S. (1986). 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