TECHNICAL FIELD

This invention relates to the adjustment of the relative percentage of casein and whey proteins in a stream of skim milk to produce dairy products with predetermined compositions and properties.

BACKGROUND ART

The physical separation of casein and whey protein using microfiltration and ultrafiltration membranes is discussed in Chapter 2 "Milk Protein Fractionation", J L Maubois and J Ollivier, in the International Dairy Federation Special Issue 9201 entitled "New Applications of Membrane Processes", (1992).

This paper reviews membrane separation technologies developed over the previous decade and discusses some applications of them. It also discusses several possibilities for which such membranes might be used.

A paper entitled "New Applications of Membrane Technology in the Dairy Industry", J L Maubois, the Australian Journal of Dairy Technology, 1991 is a further discussion of those possibilities published at approximately the same time.

Both papers, while describing some specific uses of such technology, leave open several possibilities. It is an object of this invention to go someway towards achieving those possibilities or at least to offer the public a useful choice.

European Patent Specification 542,583 describes microfiltration using diafiltration of milk followed by heat treatment and ultrafiltration to produce a concentrated product with good microbiological quality and improved coagulation. This product is intended to be used in cheese making.

In New Zealand Patent 250,399 there is described a process for concentrating skim milk by a factor of 3 to 6 times by volume using ultrafiltration or microfiltration. The process is characterised in that a quantity of lactose equivalent to the dry matter in the retentate is dissolved. It is intended to be used as a base for products such as concentrates, deserts and culinary or dietetic products.

US Patent 5,161,666 describes the ultrafiltration or microfiltration of milk and recovering the permeate from the process as a simulated human milk protein composition.

DISCLOSURE OF THE INVENTION

In one aspect the invention may broadly be said to consist in a method of adjusting the ratio of whey protein to casein in a supply of skim milk which comprises subjecting a first stream of said skim milk to microfiltration on a microfiltration membrane (as herein defined), recovering the MF retentate therefrom, and: either: a. processing said MF retentate into a first dairy product, or b. combining some or all said MF retentate with a second stream of said skim milk and optionally processing said combined stream into a second dairy product, or c. subjecting said MF retentate to ultrafiltration using an ultrafiltration membrane

(as herein defined) and recovering the UF retentate therefrom and processing said UF retentate into a third dairy product, and discarding or recovering the MF permeate from said microfiltration.

In another aspect the invention may be said broadly to consist in a method of adjusting the ratio of whey protein to casein in a supply of skim milk which comprises subjecting a first stream of said skim milk to a microfiltration on a microfiltration membrane (as herein defined), and subjecting the MF permeate therefrom to ultrafiltration using an ultrafiltration membrane (as herein defined), and either: a. recovering the UF retentate therefrom and further processing said UF retentate into a fourth dairy product, or

b. recovering the UF permeate therefrom and further processing said UF permeate into a fifth dairy product, or c. combining some or all said UF retentate and said UF permeate with a skim milk stream or a stream derived from skim milk and processing said combined stream to form a sixth dairy product, or d. combining some or all said UF retentate with a second stream of said skim milk and optionally processing said combined stream into a seventh dairy product, and discarding or recovering the MF retentate from said microfiltration.

In yet another aspect the invention may be said broadly to consist in a dairy product produced from either of the above process embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a general flow diagram of embodiments of the process of the invention for the production of milk protein concentrate, whey protein concentrate enhanced in bovine serum albumin and immunoglobulin and globular protein concentrate or isolate.

Figure 2 is a flow diagram of a process for producing a cheese milk.

Figure 3 is a flow diagram of a process for producing a whey protein depleted milk protein concentrate.

Figure 4 is a flow diagram of two embodiments of a process for producing globular protein concentrate.

Figure 5 is a flow diagram of a process embodiment of the invention for producing a cheese ingredients powder.

Figure 6 is a flow diagram of a process embodiment of the invention for producing a low fat/ high calcium milk and globular protein concentrate and isolate.

Figure 7 is a flow diagram of process embodiments of the invention for producing whey protein depleted or enhanced skim or whole milk powder and recombined skim or whole milk powder with enhanced functional properties.

Figure 8 is a plot of compressive rigidity versus strain in feta cheeses.

Figure 9 is a plot of the storage modulus (G') of globular protein concentrate and citric acid diafiltered globular protein concentrate using a Bohlin Rheometer (Sweden).

DEFINITIONS

In this specification the terms set out below have the following definitions:

Skim Milk - means skim milk separated from potable whole milk of mammals which, optionally, has been pasteurised and which includes diluted, ultrafiltered, concentrated or partly or wholly demineralised skim milk or skim milk in which the carbohydrate level has been adjusted provided always that the original percentages of casein to whey protein have remained substantially unaltered.

Volume Concentration Factor - means the ratio of the volume of the feed liquid to the retentate in an ultrafiltration or microfiltration process.

Microfiltration Membrane - means a microfiltration membrane that is permeable to water, minerals and lactose and partially permeable to whey protein and has a high retention of casein protein and fat. A microfiltration membrane typically has a pore size of 0.05 to 0.5μm, more typically 0.07 to 0.2μm.

Ultrafiltration Membrane - means a membrane which is permeable to water, minerals and lactose and has a high retention of whey proteins, casein protein and fat. An ultrafiltration membrane typically has a molecular weight cut off of less than 100,000 dalton, more typically less than 30,000 dalton.

Traditional Casein Process - means the precipitation of casein from pasteurised skim milk by traditional processes such as acidification with inorganic or organic acids or using an appropriate enzyme, such as rennin.

UHT Treatment - means sterilisation by holding at a high temperature for a short time. Typically, temperatures of 130-150°C and times of 1-120 seconds are used; more typically, temperatures of 137-145°C and times of 2-6 seconds are used.

All of the percentages in the following examples are expressed on a weight of component to weight of total composition basis.

MODES OF CARRYING OUT THE INVENTION Example 1 - Microfiltration of Skim Milk

TABLE 1 - Typical New Zealand Skim Milk Composition

Component Skim Milk

Ash (%) 0.76

Lactose (%) 5.17

Fat (%) 0.06

Casein Protein (%) 2.88

Whey Protein (%) 0.58

Total Protein (%) 3.67

Referring to Figure 1, when a skim milk 10 is subjected to microfiltration on a microfiltration membrane 12 at 50°C and a volume concentration factor of 2.5, resulting MF retentate 14 and

MF permeate 20 will have the compositions set out in Table 2. The microfiltration membrane is sold by Societe des Ceramiques Techniques (French) as a "Type Z ultrafiltration membrane".

The membrane material is mainly zirconia but other metallic oxides can be used. The pore size is O. l μm.

TABLE 2 - MF Retentate and Permeate Compositions

Component MF Retentate MF Permeate

Ash (%) 1.23 0.49

Lactose (%) 4.27 5.27

Fat (%) 0.15 <0.05

Casein Protein (%) 7.84 <0.05

Whey Protein (%) 0.96 0.36

Total Protein (%) 8.90 0.64

When the MF permeate 20 is subjected to ultrafiltration on the ultrafiltration membrane 22 at 50°C and a volume concentration factor of 35, resulting UF retentate 26 and UF permeate 24 will have the following typical compositions.

TABLE 3 - UF Retentate and Permeate Compositions

Component UF Retentate UF Permeate

Ash (%) 0.76 0.43

Lactose (%) 4.30 4.60

Fat (%) <0.5 0.00

Total Protein (%) 16.5 0.27

Although a processing temperature of 50°C was used in this and the following examples, ultrafiltration and microfiltration may typically be conducted at temperatures between about 5°C and 60°C, preferably 10°C to 50°C. The upper and lower limits are determined by factors such as undesired precipitation or denaturation well known to those skilled in the art.

Microfiltration in this and the following examples was conducted with trans-membrane pressures of less than 3 bar, preferably less than 1 bar and more preferably less than 0.3 bar.

Example 2 - Preparation of Whey Depleted Milk Protein Concentrate

Referring to Figure 1, a stream of skim milk 10 is processed by microfiltration 12 using a polymeric or a ceramic (with commercially available metallic oxide coating) membrane with a pore size of up to 0.2 μm. The preferred membrane is a zirconium oxide membrane of 0.1 μm pore size. During microfiltration volume concentration factors in the range of 1-5, more typically between 2-4, can be employed. Retentate 14 and permeate 20 result from the microfiltration process. The retentate stream contains the fat, essentially all of the casein protein and a reduced proportion of the whey protein, lactose and minerals.

The permeate stream 20 contains the remainder of whey proteins, lactose and the minerals. The retentate stream 14 can be processed by ultrafiltration 36, dewatered in evaporator 28 and dried in drier 29 to produce a milk protein concentrate 34 or retentate stream 14 can be dried in drier 29, with or without ultrafiltration 36 or with or without evaporation 28, to produce milk protein concentrate 34.

When microfiltration is enhanced by diafiltration using water, more typically demineralised water 43, the resulting milk protein concentrate will have a further whey protein depletion of up to 75% (that is, 75% of whey protein is removed and 25% remains) when three diafiltration stages are employed. The diafiltration medium can be the UF permeate 24 of ultrafiltration 22 or any other medium of similar composition as an alternative or in addition to demineralised water 43. Volume concentration factors in the diafiltration step are in the range of 1-20, more typically in the range of 5-15. The percentage removal of components from skim milk is set out in Table 4.

TABLE 4 - Percentage Depletion

Skim Milk Component Percentage Depletion

Whev Protein up to 75%

Lactose up to 99.5%

Ash up to 60%

Microfiltration 12 and ultrafiltration 36 can be manipulated by varying the ratio of diafiltration liquid to retentate to obtain milk protein concentrates having a total protein range in excess of 40% and whey protein depletion of up to 75%. Compositions of three typical milk protein concentrates prepared in this way are profiled in Table 5.

TABLE 5 - Typical Compositions of Milk Protein Concentrates

Example 3 - Production of Globular Protein Concentrate/Isolate

Referring to Figure 4, the permeate 20 from the microfiltration process 12 or the diafiltration process on the microfilter 12 or both together, are then processed by ultrafiltration 22. The retentate 26 is dried in drier 33, with or without concentration in evaporator 32, to produce globular protein concentrate/isolate stream 42 (GPC/GPI) that is low in fat. When retentate 26 is subjected to diafiltration on the ultrafilter 22 using demineralized water 43, a GPC/GPI stream 42 is recovered. The GPC contains up to 90% protein, the GPI contains >90% protein. When retentate 26 is subjected to diafiltration with acidified water, a GPC/GPI stream 42 with improved gel strength is recovered. Table 6 gives a typical compositional attributes of GPC, GPI and a whey protein isolate made using a traditional ion exchange process.

TABLE 6 - Typical compositions of GPC, GPI and a whey protein isolate

Typical amino acid profile of the GPI stream 42 is given in Table 7.

TABLE 7 - Typical Amino Acid Profile of GPI

Amino acid (%) Amino acid (%)

Cys 3,0 Tyr 4.3

His 2.1 Val 5.2

He 5.3 Ala 7.0

Leu 13.1 Arg 2.6

Lys 10.4 Asx 11.5

Met 2.3 Glx 18.4

Phe 4.2 Gly 2.0

Thr 5.6 Pro 5.1

Trp 2.0 Ser 4.8

Example 4 - Production of BSA + IG enhanced protein concentrate

Referring to Figure 1, a skim milk stream 10 is subjected to microfiltration 12 as described in Example 1. The permeate stream 20 is subjected to ultrafiltration 22 possibly including diafiltration, to produce a GPC/GPI stream 42 as in Example 3.

A retentate stream 16 which is rich in casein is processed on its own or in a blend with a second skim milk stream 11 by a traditional casein process 40 to make casein 41 and a casein whey stream 39.

The traditional casein process 40 used is as follows:

The acid casein is produced by mixing pasteurized skim milk with dilute mineral acid at 20°C to a pH of 4.6. The mixture is heated to 50-55°C to aid the agglomeration of the casein particles. Following a short period of residence in "cooking" line and "acidulation" vat, the resultant curd is separated from the whey, washed and dried (Southward, CR & Walker N L (1980) The Manufacture and Industrial Use of Casein. New Zealand Journal of Dairy Science and Technology, 15, 201-217).

The casein whey 39 will be rich in bovine serum albumin (BSA) and more importantly in immunoglobulins (IgG). The casein whey 39 can be processed by ultrafiltration 44 with or without diafiltration to produce retentate 46 which is dried in drier 49, with or without evaporator 48, resulting in a whey protein concentrate 50 enhanced in BSA and IG HPLC analysis of this WPC showed that the IG component of the protein was enhanced by 80% compared with a standard mineral acid WPC.

Typical compositions of a standard mineral acid and BSA+IG enhanced wheys are shown in Table 8 below.

TABLE 8 - Typical Compositions of Standard and BSA+IG enhanced wheys

Component Traditional mineral acid whey BSA+IG enhanced whey

Ash (%) 0.77 0.68

Lactose (%) 4.44 4.54

Total Protein (%) 0.69 0.50

Total Solids (%) 5.90 5.67

Water 94.10 94.33

BSA (% of total protein) 5 6

IgG (% of total protein) 10 18

Example 5 - Preparation of Whey Protein Depleted MPCs

Referring to Figure 3, a stream of skim milk 10 is processed by microfiltration 12 as in example 1 using a polymeric or ceramic membrane with a porosity of up to 0.2 μm, producing a retentate stream 14 with reduced whey proteins. Volume concentrations of up to 5 can be employed. The retentate stream 14 is combined with either UF permeate 24 or demineralized water 43 and diafiltered (microfiltration membranes) 12 using a concentration factor of up to 5. Further diafiltration can be carried out to achieve a further reduction of the whey protein in the retentate. The retentate is then dried 29 with or without prior evaporation 28. The MF permeate 20 is subjected to ultrafiltration 22 as in example 1. The permeate 24 is either used for diafiltration (as above) or discarded.

The composition ranges of the final milk protein concentrate are as in Table 5.

Example 6 - Use of Whey Protein Depleted MPCs

The milk protein concentrates prepared in example 5 have reduced whey protein content. The major uses of milk protein concentrates (MPCs) are recombined cheeses (soft and semi-soft), for processed cheese and cheese milk extension for natural cheese manufacture (soft, semi-soft and hard). They can provide superior functional and sensory attributes in food products like Feta cheese, Mexican Panela cheese etc.

For recombined cheeses, standard MPCs have the advantage that a high total solids (up to 40%) cheesemilk can be used. This results in very little cheese whey being produced during manufacture, and also the incorporation of the whey proteins in the cheese curd i.e. higher yields are achieved. However, the incorporation of the whey proteins has a significant effect on the functional properties of the final product. By manipulating the level of whey proteins in the MPCs one can control the functional properties of a cheese to meet the requirements of particular markets. This is a major benefit. For example in recombined soft cheeses a firmer texture cheese is produced as the level of whey protein is reduced.

In cheese milk extension, standard MPCs are used to increase cheese yields, but the whey proteins go with the cheese whey. A major benefit of a whey protein depleted MPC (of the same total protein as a standard MPC) is a further increase in yield and a decrease of whey proteins in the cheese whey.

Example 7 - The Manufacture of Recombined Feta Cheese using Whey Protein Depleted Milk Protein Concentrate

Anhydrous milk fat (AMF), milk protein concentrate (MPC) and water are mixed together to make a recombined cheesemilk with a total solids of about 40%. The cheesemilk is then homogenised and pasteurised. Cheese starter, rennet and calcium chloride are added to the cheesemilk. The product is then filled into containers and incubated at 30°C for 24 hours after which time a brine solution is added to the cheese. The cheese is stored at 5°C and is ready for consumption in about 10 days.

Recombined feta cheese was made by the above process using a standard MPC and a whey protein depleted MPC. The texture of these cheeses was measured and compressive rigidity and strain values were calculated. Figure 8 shows a plot of these values for each of the cheese samples. The cheeses made from the reduced whey protein MPCs (35 and 37) exhibited higher rigidity and lower strain values compared with the control cheeses (38 and 45). This indicates that more brittle and firmer cheese can be produced with MPCs with reduced whey protein.

Example 8 - Functional globular protein concentrates

Referring to Figure 4, a stream of skim milk 10 is processed by microfiltration 12 as in example 1 using a polymeric or ceramic membrane with a porosity of up to 0.2 μm to produce MF permeate stream 20. Volume concentrations up to 5 can be used. The pH of MF permeate stream 20 is adjusted to be ≤ 5 using organic or mineral acid 79, typically citric, hydrochloric, sulphuric or phosphoric or lactic acid (could be from lactic starters) or combinations thereof. The pH adjusted MF permeate stream 82 is then processed with or without diafiltration by ultrafiltration 22 as in example 1 to produce UF retentate stream 84, which is- dried 33, with or without prior evaporation, to generate firm gelling >80% (protein) globular protein concentrate 86, which has a superior flavour, low fat (<0.5%) and a high gel strength. Typical compositions of GPC and citric acid diafiltered GPC are given in Table 9.

TABLE 9 - Typical Compositions of GPC and of Citric Acid Diafiltered GPC

Component GPC Citric Acid Diafiltered GPC

Ash (%) 2.46 3.61

Lactose (%) 8.30 8.30

Fat (%) 0.23 0.22

Total Protein (%) 84.0 83.5

Calcium (mM/kg) 75.3 49.8

Phosphate (mM/kg) 16.8 16.4

Magnesium (mM/kg) 17.2 1 1.0

Sodium (mM/kg) 92.0 417.0

Potassium (mM/kg) 158.0 99.0

Citrate (mM/kg) 0.22 1.86

The gel strength of GPC at 11% protein and 75°C was measured to be 350 g cm ² whereas the gel strength of citric acid diafiltered GPC under the same conditions was measured to be 900 g/cm ² .

The storage modulus (G) of GPC and citric acid diafiltered GPC determined using a Bohlin Rheometer is shown in Figure 9. In Figure 9, o is globular protein concentrate, • is citric acid diafiltered globular protein concentrate and ▲ is the temperature in degrees Celsius. The results indicate that under the same temperature programming, at 120 min, the G of citric acid diafiltered GPC is about 7 times higher than the G of the standard GPC.

In a modification of the above process alternative MF permeate stream 21 can be concentrated by ultrafiltration (as in example 1) to a volume concentration factor range of 20 to 100. The preferred volume concentration factor is between 30-50. The UF retentate stream 26 is then diafiltered with acidified water 52 and dried 33 with or without evaporation to produce the >80% GPC stream 86.

Example 9 - Preparation of whey protein depleted cheese milk

It is well documented that the ratio of casein protein to whey protein varies with the stage of lactation, plane of nutrition and other factors in seasonally based pastoral farming. This affects the quality of cheese made by the process, because casein is the milk component which forms the initial gel, controlling retention of cheese yielding materials and the rate of moisture loss during processing (IDF bulletin 9301). Standardizing the cheese milk casein and whey protein levels will improve the plant efficiency and product quality. A typical process for this is as follows.

Referring to Figure 2, a stream of skim milk 10 is processed by microfiltration 12 as in example 1 using a polymeric or ceramic membrane with a porosity of up to 0.2 μm. Volume concentration factors up to 5 can be employed. The MF permeate 20 stream is processed by ultrafiltration 22 producing UF retentate 26 and UF permeate 24 streams. The whole or part of the streams of MF retentate 14, UF retentate 26, UF Permeate 24 and cream 70 are combined together resulting in a cheese milk 72 with a predetermined casein to whey protein ratio.

This ability to standardise the cheese milk content allows higher equipment utilization and optimized yield throughout the dairy season. It also gives improved process control on moisture, pH and salt-in-moisture.

The resulting cheese has consistently acceptable functional and sensory properties because of the ability to standardise the ingredient.

Example 10 - Preparation of whey protein depleted cheese ingredients powder

Processed cheese foods are food gels. The gelling properties of casein and whey proteins are different. Whey proteins gels are irreversible type whereas the casein gels are shear-thin type. Because of this it can be difficult to control the texture of mixed whey protein and casein gels. Examples are processed cheese, recombined processed cheese and stretch cheese. Standardizing the casein to whey protein ratio in the cheese ingredients would therefore help to produce products with consistent functional performance. A typical process for cheese ingredients production would be as follows.

Referring to Figure 5, a stream of skim milk 10 is processed by microfiltration 12 as in example 1 using a polymeric or ceramic membrane with a porosity of up to 0.2 μm. Volume concentrations up to 5 can be employed. The permeate 20 is processed by ultrafiltration 22 as in example 1 producing UF retentate 26 and UF permeate 24 streams. The MF retentate 14, UF retentate 26, UF Permeate 24 and cream 70 are combined together resulting in stream 74 which is dried in drier 29, with or without evaporation, resulting in a cheese ingredients powder 76 with a predetermined casein to whey protein ratio.

The cheese ingredients powder may be used for processed cheese, recombined cheeses and cheese milk extension.

Example 11 - Low Fat/High Calcium UHT Milks

Referring to Figure 6, a stream of skim milk 10 is processed by microfiltration 12 as in example 1, using a polymeric or ceramic membrane with a porosity of up to 0.2 μm. The volume concentration factor should be carefully selected such that the calcium level in the final product is greater than 0.2% but the fat level is below 0.1%. For the typical skim milk composition (as set out in Table 1) containing 0.12% calcium, typical volume concentration factor is 1.5. The retentate 14 can then be processed in a UHT plant 90 to produce a low fat/high calcium milk 94.

Optionally, retentate 14 can be obtained by processing the skim milk to a typical volume concentration factor of 2, blended with skim milk 10 at appropriate ratio to produce blended milk 88 having a calcium content that is greater than 0.2%, a fat content that is less than 0.1%. The blended milk is then processed in a UHT plant 90 to produce low fat/high calcium milk 94. In another option, retentate 14, MF permeate 20 and UF permeate 24 can be carefully blended in appropriate ratio, such that blended milk will have a calcium level that is greater than 0.2% but a fat level that is less than 0.1%. The blended milk 89 is then processed in a UHT plant 90 to produce a low fat/high calcium milk 94.

The compositions of low fat/high calcium UHT milks with reduced whey protein levels are set out in Table 10. These products displayed better long-term storage characteristics (6-8 months), particularly increased resistance to gelation compared with low fat/high calcium UHT milks produced by ultrafiltration (4-7 months). If the UHT operation is not used, the low fat/high calcium milk can be sold for local markets with or without further heat treatment.

TABLE 10 - Low Fat/High Calcium Milk Composition

Component Compositions

Total Solids 10-13%

Water 87-90%

Total protein 5-6.5%

Minerals 0.9-1.2%

Lactose 4-5.5%

Calcium iθ.2%

Fat ≤0.1%

Example 12 - Manufacture of Milk Powders through Partial Separation of Casein

Protein and Whey Protein Fractions

Milk powders for recombining and reconstitution rarely exhibit ideal performance in the applications for which they were intended. Many of these shortcomings seem to be linked to milk

composition and in some cases it seems that relatively minor changes in composition can lead to remarkable improvements in performance. In particular, it has been found that the ratio of casein protein to whey protein has an important influence on the performance of milk powders in several applications. Moreover, it has been found that the efficiency of milk powder manufacture is determined to a large extent by the relationship between milk viscosity and total solids, which is in turn strongly dependent on the casein protein to whey protein ratio of the milk being dried. The following describes how microfiltration can be used in a milk powder production plant to manipulate the composition of milk in order to improve both the processing of the milk and the performance of the subsequent milk powder.

Referring to Figure 7, a typical skim milk 10 is processed by microfiltration 12 as in example 1 using polymeric or ceramic membranes with a pore size of up to 0.2 μm. Appropriate volume concentration factors for the microfiltration process are selected depending upon the protein concentration of the milk stream being microfiltered. For New Zealand skim milk (which typically contains about 3.5% protein), volume concentration factors of 1.5 to 4 are best employed. The MF retentate 14 contains most of the casein and some (typically 50-80%) of the whey protein found in the original skim milk 10. The MF permeate 20 contains almost no casein but part of the lactose, free minerals and whey proteins (typically 20-50%) found in the original skim milk 10. Thus the MF process separates skim milk into a whey-protein-contained stream (the MF permeate 20) and a whey-protein-depleted stream (the MF retentate 14). These streams can be further processed in various ways to produce milk powders that have adjusted casein protein to whey protein ratios (see schemes 1 and 3 below). Alternatively, the two streams (14 and 20) can be subjected to different processing regimes (e.g., different heat treatments) before being recombined and evaporated and dried to produce a milk powder that is identical to a standard milk powder in compositional terms but that has an improved balance between functional and/or flavour properties (see scheme 2 below).

Scheme 1 : Whev-Protein-Enhanced Milk Powders

The MF permeate 20 is processed by ultrafiltration 22 to produce a UF retentate 26 and a UF permeate 24. The UF retentate 26 contains typically 20-50% of the whey protein found in the original skim milk 10 and can be combined with a second stream 11 of the original skim milk to produce a whey-protein-enhanced skim milk 55. The UF retentate 26 and the skim milk 10 can

each be -further processed in any manner before being mixed to form whey-protein-enhanced skim milk 55 if this is desired. Cream 70 may or may not be added to 55 and the resulting whey- protein-enhanced whole milk or whey-protein-enhanced skim milk can then, optionally, be evaporated on an evaporator (which is not shown) and subsequently dried on drier 47 to produce a whey-protein-enhanced whole or skim milk powder 60.

Whey-protein-enhanced powders have been found to perform better than standard powders in recombined cultured products. For example, use of whey-protein-enhanced powders in the manufacture of recombined yoghurts leads to reduced syneresis and increased gel strength compared with yoghurts made from standard powders. Similarly, cultured beverages made from whey-protein-enhanced powders show reduced sedimentation and shorter fermentation times than cultured beverages made from standard powders

Scheme 2: Milk Powders with Standard Composition The MF permeate 20 is recombined with the MF retentate 14 after one or both streams have been subjected to further processing. This may involve simply subjecting the MF retentate 14 and the MF permeate 20 to different heat treatments before recombining the two streams and evaporating and drying or it may involve further separations. For example, the MF permeate 20 may be processed by ultrafiltration 22 to produce a UF permeate 24 and a UF retentate 26. The UF retentate 26 contains typically 20-50% of the whey protein separated from the original skim milk 10 and the UF permeate 24 contains most of the lactose and most of the free minerals separated from the original skim milk 10. Each of streams can then be subjected to different heat treatments and/or any other desired processes before all streams are recombined to produce a skim milk 56 that has identical composition to a standard skim milk. Cream 70 may or may not be added to the skim milk 56 to produce a whole milk or a skim milk 56 which can then, optionally, be evaporated on an evaporator (which is not shown) and subsequently dried on drier 47 to produce a whole milk powder or a skim milk powder 59. Careful selection of the heat treatments for each stream allows production of skim or whole milk powders with desired combinations of functional and flavour properties.

Evaporation of whey protein depleted streams like the MF retentate 14 can typically be continued to higher total solids than standard skim milk. As a result, the overall evaporation and drying of