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International Dairy Journal 18 (2008) 735– 740

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International Dairy Journal

0958-69

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Review

Membrane processes in dairy technology—From a simple idea toworldwide panacea

Yves Pouliot �

STELA Dairy Research Center, Institute of Nutraceuticals and Functional Foods (INAF), Pavillon Paul-Comtois, Universite Laval, Qc, Canada G1K 7P4

46/$ - see front matter & 2008 Elsevier Ltd. A

016/j.idairyj.2008.03.005

+1418 656 5988; fax: +1418 656 3353.

ail address: Yves.Pouliot@inaf.ulaval.ca

a b s t r a c t

Membrane technology has been applied in the dairy industry since the early 1970s. The applications of

membrane processes are used as alternative to some unit operations, in the solving of separation issues

and in the development of new dairy products. The contemporary pressure-driven membrane units

include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) and the

main applications are related to dairy-based protein ingredients, pre-concentration of milk before

cheese manufacture and alternative technology for extending shelf life of milk. The development of

value-added products from minor milk compounds represents one of the most promising applications

of membranes in dairy. Important challenges worldwide face membrane technologies in the near future.

& 2008 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735

2. Membranes and dairy technology: four decades of innovations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736

3. Membrane processes at the turn of the new millenium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737

3.1. Manufacture of dairy-based protein ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737

3.2. Pre-concentration of milk before cheese manufacture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738

3.3. An alternative technology for extending shelf life of milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738

4. The future of membrane processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

4.1. Tools for new value-added products from milk and whey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

4.2. Technological challenges worldwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740

1. Introduction

The idea of using a membrane as a tool for separation probablydates back to the 18th century when, for example in 1748, AbbeNolet first used the word osmosis to describe the permeationof water through a diaphragm made of a pig’s bladder (Baker,2004). Triggered by the needs to study laboratory phenomenasuch as osmotic pressure, membranes have later been used byvan’t Hoff, who developed the limit’s law in 1887. The firstmembranes developed for separation purposes and having gradedpore size were made of nitrocellulose (collodion) and theircommercialization began in the 1930s. Unsuccessful attempts to

ll rights reserved.

produce pure drinking water using these membranes werereported during World War II in Germany, Europe and also inthe United States.

The growing concerns about the drinking water supply inSouthern California stimulated the establishment of researchprograms on water desalination at the University of California inLos-Angeles (UCLA), where the first defect-free, high-flux aniso-tropic reverse osmosis (RO) membrane was developed in the early1960s. Two UCLA graduate students, Sidney Loeb and SrinivasaSourirajan (who later became a researcher at the NationalResearch Council of Canada), discovered an effective way to makeRO membranes (Loeb & Sourirajan, 1963). Their lab-scaledesalination unit, the so-called big dripper, was producing modestamounts of fresh water but it gave birth to a multi-billion dollarworldwide industry. The discovery of asymmetric membranes byLoeb and Sourirajan is often referred to as the starting point of

ARTICLE IN PRESS

Table 1Milestones in the development of membrane technology and its applications in

dairy processes since 1960s

Advances in membrane technology Applications of membranes in

dairy processing

1960s � Development of reproducible

membranes by manufacturers

1970s � Materials with improved chemical

resistance (from cellulose acetate

to polysulfone)

� First designs of sanitary modules

� Design of whey pre-treatments

to prevent membrane fouling

� Development of processes for

the UF of acid whey

� Development of the first

UF-based cheese manufacture

processes

1980s � Improvement of membrane system

hardware (module designs, spacers,

anti-telescoping devices)

� Development of commercial

inorganic (ceramic) membranes

� Using UF or RO membranes to

concentrate milk on farm

� Defatting of whey (WPI

membranes, recovery of minor

compounds)

� Separation of b-lactoglobulin &

a-lactalbumin

� Desalting whey with loose-RO

(NF) membranes

1990s � Improvement of hydrodynamics of

MF membranes (UTP)

� Porosity gradient membranes

� Control of particle’s deposition

(vibration, rotating disk, Dean’s

vortices, static mixer)

� Functionalized membranes (ion

exchange)

� Removing spores from cheese

milk and whey

� Defatting whey

� Separating casein micelles

from milk (ideal whey)

� Extending milk’s shelf life

(ESL milk)

� Fractionating hydrolysates

using UF/NF membranes

Y. Pouliot / International Dairy Journal 18 (2008) 735–740736

modern membrane science and is viewed as the cornerstone ofindustrial membrane processing.

Processing of milk and dairy products has greatly benefitedfrom this technological development as a number of unitoperations involve either water removal, solid–liquid or liquid–li-quid separations. The purpose of this paper is to review some ofthe main technological advances that were made possible throughmembrane processing and to highlight some promising applica-tions of membranes for future developments. This overview willfocus on pressure-driven membrane process since, apart fromelectrodialysis, which has been used extensively in the deminer-alization of cheese whey for infant formulas, the other electricallyassisted technologies are still under development at laboratory orpilot scale.

2. Membranes and dairy technology: four decades ofinnovations

The number of successful applications of membranes devel-oped for the processing of milk and dairy products since the 1970sare important and ever increasing. The development of these newapplications was often a direct result of evolution of membranescience. In a number of instances, some key technological issuesneeded to be resolved before membranes could be applied in dairyprocessing. Table 1 summarizes the most important milestonessince the first years of industrial membrane technology, alongwith some significant developments that occurred in dairyprocessing.

The 1960s correspond to the early days of industrial membranemanufacture. Reproducibility and resistance (chemical andmechanical) of membrane materials were the two main obstacles

for the development of industrial application of membranes.Cellulose acetate (CA) anisotropic membranes were the first toreach industrial scale but their limited sensitivity to extreme pHconditions was shortening their lifetime. Ultrafiltration (UF) wasproposed as a potential technique to concentrate milk solids,mainly proteins. However, dairy applications required sanitarymodule designs, which were still difficult to achieve in the late1960s.

Sanitary tubular (T) and plate and frame (PF) UF modules weredeveloped for industrial applications in the 1970s. Polyamide (PA)membranes became available for RO. Polysulfonic (PS) membranematerials, having better chemical stability than CA, wereintroduced in a new hollow fiber (HF) configuration. The 1970shave seen the rise of UF as a technique to pre-concentrate milkbefore cheese making and to recover proteins from whey. Thedecade was marked by the first attempts to produce industrialcheeses from UF retentates (or liquid pre-cheese), following theMMV procedure patented by Maubois, Mocquot, and Vassal(1969). The MMV process was first applied in France tomanufacture Camembert cheese. The SiroCurd process, anotherUF-based approach using lower concentration factors and moresuitable for hard and semi-hard cheeses, was developed inAustralia. These innovations triggered the development of a largenumber of UF-based cheese manufacturing approaches in thefollowing two decades (see Section 3.2). The preparation of wheyprotein concentrates (WPC) reached industrial scale, whilesignificant research effort was devoted to the development ofprocess conditions for the separation and concentration ofproteins from cheese whey by UF. The market for WPCs was inits infancy, and hence, much effort was devoted to developapplications of these ingredients in food systems until the early1980s. From the technological standpoint, the main challenge wasto design pre-treatments to prevent fouling during UF of whey. Anumber of these pre-treatments are still used in whey-processingplants (Pouliot & Jelen, 1995). Some attention was also given to theuse of nanofiltration (NF) for conversion of acid whey into sweetwhey by means of pH adjustments and diafiltration.

The 1980s have seen the rise of commercial NF (or loose RO)membranes, mainly as a result of efficient manufacturingprocesses for thin-film composite (TFC) membrane materialsusing known polymers (PA, PS, CA) but membrane reproducibilitywas still a challenge. The initial enthusiasm for new processdevelopment based on UF concentration of milk for cheesemanufacture was somewhat affected by mitigated economic dataon cheese yields. In addition, the use of UF pre-concentrated milkwas often found to have negative consequences for cheeseripening (Horton, 1997a). On-farm RO and UF concentration ofmilk was also evaluated in various parts of the world. The WPCindustry was propelled by new applications for whey proteins asfunctional ingredient in food systems. The development of wheydefatting approaches (thermocalcic aggregation, acid precipita-tion) also opened the way to the production of whey proteinisolates (WPI) using UF membranes (Pearce, 1992).

While NF reached industrial scale and was used worldwide bythe dairy industry to desalt whey, mother liquors and brines,microfiltration (MF) has also marked the 1990s (Horton, 1997b,1997c). Commercial ceramic membranes and the uniform trans-membrane pressure (UTP) concept (Sandblom, 1974) for the controlof hydrodynamics and fouling during MF of dairy fluids wereintroduced. This innovation led to the solving of technologicalproblems such as late blowing Emmental cheeses, removal ofspores from whey, efficient defatting of milk and whey, andseparation of casein micelles from milk. New concepts of extendedshelf life (ESL) milks were elaborated using MF for the removal ofbacteria from milk. MF in combination with physicochemicalmodification was also applied to separate b-lactoglobulin (b-LG)

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Y. Pouliot / International Dairy Journal 18 (2008) 735–740 737

from a-lactalbumin (a-LA). The separation of b-casein from milkhas been achieved at industrial scale by MF under a combination ofphysicochemical conditions (cooling, pH adjustment, salt addi-tions) as proposed by Terre, Maubois, Brule, and Pierre (1987).

Other MF membrane concepts such as the Membralox GPs

(Societe des Ceramiques et Techniques, France) and the Isofluxs

(Tami, France) were later developed to minimize membranefouling resulting from excessive pressure drop. Other approachessuch as backpulsing, air slugs, rotating or vibrating modules weredeveloped to minimize fouling or particle deposition during MF(Brans, Schroen, van der Sman, & Broomr, 2004) but very fewmade it to the industrial scale. Functionalized membranematerials such as ion-exchange membranes emerged in the1990s. The technique combines the selectivity of ion-exchangechromatography and the productivity of membrane separations.However, their low binding capacity (per unit of membrane area)and their limited lifetime are still limitative and so the techniquehas been used mainly at laboratory scale.

The commercial availability of new NF materials allowed thedevelopment of approaches to separate milk and whey peptidesfrom enzymatic hydrolysates (Gauthier & Pouliot, 1995). Althoughmilk and whey protein hydrolysates had been known andmanufactured since the 1980s for nutritional and clinicalapplications, the demonstration of some biological activities(antihypertensive, calcium-binding, immunomodulatory) in milkand whey peptide sequences triggered the development of theseapproaches for peptide separation.

3. Membrane processes at the turn of the new millenium

Membrane separations are nowadays well integrated in thedairy industry. Timmer and Van der Horst (1998) estimated thetotal area of UF and RO membranes installed worldwide to bearound 210,000 and 60,000 m2, respectively. Over 75% of thesetotal areas for UF and RO are dedicated to whey processing, whilemilk processing accounts for 25% of UF membranes.

The applications of membrane processes in dairy processingcan be classified into three main areas (Fig. 1), namely: (1)alternatives to some unit operations such as centrifugation,evaporation, debacterization and demineralization, (2) means to

Alternatives to unit operations

Creating new products

Resolvingseparation

issues

Centrifugalseparation(Skimming)

Water removal (evaporation)

UF-cheeses

Control over bacteria(heating)

Demineralization(electrodialysis)

Textured milk products

Beverages

(UF-permeate)

Extended shelf life milk (ESL)

Removingspores from skimmilk and whey

Defatting whey

Removingcasein micellesfrom milk

Separatingproteins/peptides

Extracting whey Proteins (WPCs)

Recycling brine & cleaning solutions

Fermented milks

Fig. 1. Membrane processes in the dairy industry: a look at the applications.

resolve separation issues such as defatting of whey, proteinrecovery and separation, milk fat globule fractionation (Goude-dranche, Fauquant, & Maubois, 2000), or recycling of solutionsand spores removal, and (3) tools to create new dairy productssuch as UF cheeses (Ras, Pave d’Affinois, Domiati, etc.), ESL milk,whey-based beverages and textured milk products. This simpleclassification highlights the versatility the membrane processeshave acquired over the years and their wide range of applicationsin the dairy industry.

Two other important applications of membrane processes thatcould not be classified in Fig. 1 are the standardization of milkproducts using milk UF permeate (Puhan, 1991) and on-farm UFfor the reduction of milk transportation costs (Zall, 1987a, 1987b).The addition of UF permeate to milk enables its standardization inprotein, fat and non-fat solids of milk and dairy products.Moreover, it was found that this practice had no measurableimpact on the organoleptic properties of skim milk (Rattray &Jelen, 1996). On-farm UF for the reduction of milk transportationcosts has been evaluated in Australia, USA, Canada and other partsof the world. Technological feasibility has been demonstrated butthe economic viability of that process is variable and stronglydependent on the costs for the disposal of the UF permeategenerated on farm (Renner & Abd El Salam, 1991).

The contemporary use of membranes in dairy processing hasbeen reviewed in International Dairy Federation special issuespublished in 1991 and 2004, and by some other authors (Moresi &Lo Presti, 2003; Rosenberg, 1995). However, we must acknowledgethat three applications have brought significant changes in thedairy industry worldwide, namely manufacture of milk and wheyprotein ingredients, pre-concentration milk before cheese making,and bacteria and spores removal for ESL milks.

3.1. Manufacture of dairy-based protein ingredients

Membrane processes have been widely used to develop andmanufacture dairy-based proteins ingredients from milk or whey.Table 2 summarizes the well-known filtration spectrum ofmembrane processes applied to milk constituents. MF, UF, NFand RO membranes are characterized by pore sizes ranging from40.1mm to o0.1 nm and by operating pressures from 0.01 to5 MPa. The highest operating pressures are observed with NF andRO membranes, where membrane pore sizes and porosity aresmallest and where applied pressures must be higher than theosmotic pressure osmotic pressure of the feed to allow permea-tion. Polymeric and inorganic membrane materials are availablefor the entire range but UF offers the widest variety of moduleconfigurations, including HFs, in addition to T, PF and spiralwound (SW). Separations using RO, NF, UF and MF cover the entireseparation domain of milk constituents, from casein micelles tomonovalent ions. Most of these processes achieve the separationof milk constiuents by molecular sieving or size separation. Thesurface morphology and internal structure of UF and NFmembranes, as affected by pH and ionic strength, can alsointroduce steric effects. In addition, some UF membranes andmostly NF membranes are electrically charged and phenomenasuch as electrostatic interactions and Donnan effects canpredominate their separation mechanisms.

Numerous technological options for concentrating and purify-ing milk or whey proteins using membranes have been exten-sively described elsewhere (Hobman, 1992; Maubois & Ollivier,1991; Mehra & Kelly, 2004; Rosenberg, 1995; Zydney, 1998).

Table 2 also lists the main commercial ingredients originatingfrom milk. Total milk proteins (TMP) are obtained by UF, whereasmicellar caseins (MC) or phosphocaseinate are obtained byMF separation of milk. UF is also used in the manufacture of

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Table 2Filtration spectrum available for the separation of milk constituents

Pore sizea Separation

mechanism

Operating pressure

(MPa)

Membrane

materialsb

Module

configurationc

Separation domain Membrane-based commercial dairy ingredientd

MF 40.1 mm Sieving 0.01– 0.2 Inorganic

polymeric

T, MC Somatic cells, bacteria, spores Micellar casein,

Fat globules Native whey proteins

Casein micelles

UF 1– 500 nm Sieving & charge 0.1– 1.0 Inorganic

polymeric

T, HF, SW, PF Soluble proteins

Caseinomacropeptide

WPC, WPI, MPC, b-LG, a-La,

NF 0.1–1 nm Sieving & charge 1.5–3.0 Inorganic

polymeric

T, HF, SW, PF Indigenous peptides Salts

(divalent cations)

Bioactive Milk & whey protein hydrolysates,

Glycomacropeptide

RO o0.1 nm Sieving,

diffusion

3.0–5.0 Polymeric SW, PF Salts (monovalent cations)

Lactose

Whey permeate Delactosed, deproteinized

whey

a Data in columns 2–6 were collected from reference books on membrane separations (Mulder, 1996; Cheryan, 1998).b Polymeric: cellulosic, polysulfone, polyamide; inorganic: ceramic, carbon-supported zirconium oxide, stainless.c T, tubular; MC, multichannel; HF, hollow fiber; SW, spiral wound; PF, plate and frame.d WPC, whey protein concentrate; WPI, whey protein isolate; MPC, milk protein concentrate.

Table 3Approaches to integrate membrane processes in cheese-making practicea,b

Approaches Type of cheese

UF retentate (VCR: 1.2-2X)1 Cheddar, Cottage, Mozzarella, Saint-

Paulin, Brick, Colby, Edam, Quarg

UF retentate (VCR: 2-6X)1 Cheddar, Feta, Havarti, Gouda, Blue

cheese

Liquid pre-cheese1 Camembert, Quarg, Saint-Maure,

Ricotta, Cream cheese, Mascarpone,

Feta, Mozzarella, Saint-Paulin

MF-treated milk (low VCR and DF

with milk permeate)2

Cheddar, cottage

MF retentate (VCR: 5-8X)3 Mozzarella

Adding UF retentate to cheese milk4 Parmesan

Adding PC, MPC or UF retentate to

standardize cheese milk5

Cheddar

a The table content was extracted from: 1Rosenberg (1995); 2Nelson and

Barbano (2005); 3Madsen and Qvist (1998), Brandsma and Rizvi (2001);4Govindasamy-Lucey, Jaeggi, Bostley, Johnson, and Lucey (2004); 5Guinee,

O’Kennedy, and Kelly (2006).b VCR, volumic concentration ratio; DF, diafiltration; PC, phosphocaseinate;

MPC, milk protein concentrate.

Y. Pouliot / International Dairy Journal 18 (2008) 735–740738

whey-protein-based ingredients such as WPCs, isolates (WPI) andsome concentrated fractions of b-LG and a-LA or glycomacropep-tide (GMP). NF has been used for desalting milk, whey and otherdairy fluids (Horton, 1998; Kelly, Horton, & Burling, 1991; Van derHorst, Timmer, Robbertson, & Leenders, 1995) and thus it is usedin the preparation of whey delactosed and deproteinized whey.Finally, RO is nowadays widely used to increase the total solids(TS) content of liquid fractions resulting from membrane separa-tions of dairy components before spray drying.

3.2. Pre-concentration of milk before cheese manufacture

The possibility of using UF to pre-concentrate milk beforecheese making was very attractive and so it has been extensivelyexploited for a wide variety of cheeses in many differenttechnological variations (Henning, Baer, Hassan, & Dave, 2006).

The MMV process (Maubois et al., 1969) constitutes the firstexample of UF-based cheese process, where a 5-7X volumicconcentration factor is applied to milk before cheese making. TheMMV process generates less whey and increases yields by a15–20% margin as a result of whey protein retention in curd andhigher humidity. The advantages are increased capacity of cheesevats, decreased costs in rennet per kg of cheese, potentially

adaptable to continuous operations and uniformity of the curd.Higher viscosity and buffering capacity of the UF retentate,compared to cheese milk, necessitates adjustments in thecheese-making process. The MMV process was best suited forfresh and soft-ripened cheeses. It has also been successful withFeta cheese despite the fact that the process induces changes incheese texture and impairs its meltability by incorporating morewhey proteins in the curd.

Table 3 reports some of the recent approaches that have beendeveloped since the pioneer MMV process. The list from Table 3 isnot exhaustive since the process for producing a much widervariety of hard, semi-hard, soft and fresh cheeses have beenadapted using UF or MF pre-concentration of cheese milk. Tosummarize, three levels of UF-pre-concentration of milk havebeen used: low-retentate concentration (VCF: 1.2-2X) oftenreferred to as LCR, medium retentate concentration (VCF: 2-6X)and liquid pre-cheese (FCV: 6-8X). The use of MF to pre-concentrate milk enables not only the standardization of proteincontent of milk but also the casein to total protein ratio (Johnson& Lucey, 2006). More recent practices have however been to addUF retentates, milk protein concentrates (MPC) and even phos-phocaseinate to cheese milk in order to increase productivity ofcheese plants.

3.3. An alternative technology for extending shelf life of milk

The development of the UTP concept by Tetra-Laval (Sandblom,1974) has allowed the introduction MF at industrial scale. The UTPconcept is defined by a membrane cartridge in which thepermeate is recirculated in a co-current direction along theretentate, ensuring a minimal (Ptmo0.05 MPa) and constantpressure drop along the membrane axis, and therefore minimizingfouling. The membranes are made of alumina or ceramic, whichalso offer distinctive advantages related to chemical resistance toheat and chemicals and better control over membrane pore sizedistribution. MF multichannel membrane elements with 1.4mmpore size were shown to decrease the mesophilic counts,salmonella and Listeria by a 2–3 decimal factor in milk (Madec,Mejean, & Maubois, 1992). It was also shown that MF was notinducing significant changes in overall milk composition (Bindith,Cordier, & Jost, 1996). The UTP device was introduced in the Bacto-catchTM process in order to produce ESL milks. It is for examplepossible to produce fluid milks having o30 cfu mL�1 mesophilliccounts (compared with 900–3000 mL for conventional pasteur-ized milk; Saboya & Maubois, 2000). This translates into shelflife extension from 12 to 45 days at 4 1C (Goff & Griffiths, 2006).

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Y. Pouliot / International Dairy Journal 18 (2008) 735–740 739

A tangible example of this application is Pure filters, a fluid milkissued from the Bacto-catchTM technology and currently commer-cialized by Parmalat Canada.

4. The future of membrane processes

4.1. Tools for new value-added products from milk and whey

Utilization of the minor components from cheese whey stillrepresents a challenge for whey ingredient manufacturers(Horton, 1995; Huffman & Harper, 1999). Membrane processesare now viewed as efficient tools for the development of newvalue-added products by separating minor compounds such asbioactive peptides, growth factors and oligosaccharides from milk,whey or fermented dairy-based media.

The concept of bioactive peptides derived from food proteinshas been developed in the 1980s and since then, a world-wide interest for bioactive peptide is growing in the scientificcommunity.

It is now established that pressure-driven membrane-basedprocesses, such as UF and NF, can be used to fractionate peptidemixtures and amino acids (Groleau, Lapointe, Gauthier, & Pouliot,2004). NF separations are especially attractive since they canachieve peptide separations based both on their size and charge. Asignificant advantage of membrane processes such as UF or NF isthat membranes can be added to the production process ofbioactive peptides (by hydrolysis or fermentation), and theproduct can be separated continuously in the so-called bioreac-tors (Pouliot, Gauthier, & Groleau, 2005).

Growth factors such as transforming growth factor b (TGF-b)and insulin-like growth factor I and II (IGF-I and II) have beentypically separated from whey by means of cation-exchangechromatography (Smithers, 2004). However, some recent devel-opments of membrane applications have enabled the recovery ofgrowth factors from whey (Gauthier, Pouliot, & Maubois, 2006;Pouliot & Gauthier, 2006). Cheese whey has been privileged forthe extraction of milk-derived growth factors, mainly because ofthe availability of the substrate. However, since bovine colostrumtypically contains 10–15 times the amount of milk in terms ofgrowth factors, it has recently garnered some attention, andtechniques based on MF/UF separations have been proposed forthe extraction of immunoglobulins and growth factors to producehealth ingredients (Piot, Fauquant, Madec, & Maubois, 2004).Provided some solid scientific evidences on their bioactivity inhumans are developed, a sustainable market can be expected for

Table 4Future challenges for membrane separationsa

Problem Separation issues

Management of water supply & uses � Re-use water

� Minimize dilution

� Produce drinking water

Separation/purification of high-value

minor compounds� Cost-effective processes

� Selectivity

� Reproducibility

Control on the energy consumption � Control of fouling

� Alternative/renewable energy sources

Sanitary/biosecurity � Decontamination (pathogens)

� Prevention/intervention bioterrorism

a From Noble and Agrawal (2005).

these new bioactive milk fractions (Regester, Belford, West, &Goddard, 2003).

Other minor compounds such as oligosaccharides or MFGMproteins (Spitsberg, 2005) may in the near future offer someopportunities for new bioactives; but in the meantime, supportingdata on the physiological effects of growth factors are still needed.It appears that membrane technologies have still not been fullyexploited in the dairy industry for the development of milk-basedingredients. This is mainly due to commercial constraints such aslow or immature market demand for value-added ingredients,occurrence of alternative technologies or introduction of non-dairy equivalents of dairy ingredients.

4.2. Technological challenges worldwide

Although a wide variety of fascinating new applications ofmembrane technology in dairy processes are expected in the nextdecade, the field of membrane science is facing importantchallenges worldwide such as shortage of drinking water supplies,global warming and potential global energy crisis. A recent reviewby Noble and Agrawal (2005) covering all separation technologiespointed out some issues related to membrane processes (Table 4).The development of units and process designs that minimizes theuse of water is becoming critical. The cost-effectiveness ofmembrane processes will become increasingly important sinceother separation techniques are becoming available. Selectingmembrane separation often means compromising betweenselectivity and productivity. New membrane chemistries, bio-affinity membranes or new materials emerging from nano-technologies are likely to revolutionize the field of membranescience in the next decade. With the costs of fossil fuels constantlyon the rise, it is imperative that control of energy consumptionwill be a key factor in the development and growth of membrane-based processes in the future. Control of fouling will undoubtedlyremain as a high-priority research domain, whereas developmentof new module designs using renewable energies might offerinteresting alternatives. Finally, environmental pollution andother threats such as bioterrorism are among the growingphenomena that will typically require self-powered, small andmobile RO units to produce in situ drinking water in many parts ofthe world.

5. Conclusion

The development of membrane processes and their integrationin dairy technology has occurred in many steps along with thedevelopment of membrane science itself. Membrane separationshave revolutionized the field of dairy processing in many aspects.It has been part of profound changes in the dairy industryworldwide. Bovine milk’s entity is now challenged since manyseparation processes are available and many of its constituentscan be removed. Although this view can be considered asthreatening for the image of milk as nature’s gift, perhaps weshould remember how centrifugal separations, almost a centuryago, have in their way revolutionized the early days of fluid milkprocessing.

Acknowledgments

The author wishes to thank the Natural Sciences andEngineering Research Council of Canada (NSERC), Fonds Quebe-cois de Recherche Nature and Technologies (FQRNT) and NovalaitInc. for their financial support to his research projects onmembranes in dairy processing.

ARTICLE IN PRESS

Y. Pouliot / International Dairy Journal 18 (2008) 735–740740

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