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Non- applications of components and co-products: A review Jean-Luc Audic, Bernard Chaufer, Georges Daufin

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Jean-Luc Audic, Bernard Chaufer, Georges Daufin. Non-food applications of milk components and dairy co-products: A review. Le Lait, INRA Editions, 2003, 83 (6), pp.417-438. ￿10.1051/lait:2003027￿. ￿hal-00895512￿

HAL Id: hal-00895512 https://hal.archives-ouvertes.fr/hal-00895512 Submitted on 1 Jan 2003

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Lait 83 (2003) 417–438 © INRA, EDP Sciences, 2003 417 DOI: 10.1051/lait:2003027 Review

Non-food applications of milk components and dairy co-products: A review

Jean-Luc AUDICa*, Bernard CHAUFERa, Georges DAUFINb

a Laboratoire des Procédés de Séparation, Université de Rennes 1 (UC INRA), Campus de Beaulieu, Bât. 10A, CS 74205, 35042 Rennes Cedex, France b Laboratoire de Recherches de Technologie Laitière, INRA, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France

(Received 31 March 2003; accepted 20 June 2003)

Abstract – Milk contains a lot of different components with their own functional properties and some of them, such as casein, have been used in the manufacture of non-food technical products for many years. The present review deals with the non-food applications of (i) the major individual components of milk: (casein; soluble proteins); lactose; milk fat and (ii) , a co-product of and casein manufacture. New applications of milk proteins on a laboratory scale are focused on the manufacture of -based films and biomaterials. Also, fermentation of lactose and whey provides low molecular weight compounds and exopolysaccharides. These promising routes for giving added value to dairy co-products and effluents should be applied to achieving a great reduction in dairy industry wastes.

Non-food application / casein / lactose / whey / / milk fat / fermentation

Résumé – Applications non-alimentaires des constituants du lait et des coproduits de l'industrie laitière : revue. Le lait est composé de différents constituants présentant chacun des propriétés fonctionnelles caractéristiques et ayant été valorisés dans le domaine non-alimentaire depuis de nombreuses années. L’objectif de cet article est de passer en revue ces applications non- alimentaires pour (i) les constituants individuels majoritaires du lait pris séparément à savoir : protéines (caséines ; protéines solubles), lactose, matière grasse ; et (ii) le lactosérum, co-produit de la transformation du lait en fromage ou en caséine. La fabrication de films et de biomatériaux à base de protéines apparaît comme l’une des applications les plus récentes et les plus attractives. D’autre part, la fermentation du lactose et/ou du lactosérum permet d’obtenir une grande variété de composés de faible masse molaire ainsi que des exopolysaccharides eux-mêmes valorisables. La variété des applications non-alimentaires répertoriées permet d’envisager différentes voies de valorisation pour les co-produits et les effluents de l’industrie laitière dans l’objectif de réduire au maximum les rejets.

Application non-alimentaire / caséine / lactose / lactosérum / protéine du lactosérum / matière grasse / fermentation

* Corresponding author: [email protected] 418 J.-L. Audic et al.

1. INTRODUCTION macological industries [58, 63] and the manufacture of protective films or coatings Milk and milk components are mostly [28, 90]. used in foodstuffs in many different forms. In the second part of this review techni- Nevertheless, milk constituents also find cal applications for lactose are discussed. numerous alternative applications in the Because of its low digestibility and solubil- non-food area such as in the manufacture of ity, lactose finds limited applications in the materials [138], fibres [44], food area compared with some other sug- glues [143] or in the production of ethanol ars, making alternative applications of or methane [71]. Some of these technical prime interest. In relation to its functional applications have been well known for a properties and the number of its reactive long time, such as casein-based glues which sites, lactose is used as a raw material for were used in ancient Egypt [143], but novel special applications, for example, in phar- uses are also proposed for opening new macology [64], as for fermenta- markets for components. Most of the tech- tion of various products [64, 71, 163] nical applications are specific to one given (methane, ethanol…) and in the synthesis milk component in relation to its structural of derivatives [145, 163] such as lactulose and functional properties. Separation and or lactitol, the best known examples. Par- extraction techniques may be of impor- ticular attention was paid to non-food uses tance in the valorisation process of such of lactose from whey. Whey, a co-product individual components. Valuable compo- of cheese-making and casein industry, con- nents can be recovered by chemical and/or tains the -soluble components of milk: physical means in milk and dairy coprod- lactose, whey proteins, salts and vitamins. ucts: casein is precipitated by adjusting pH Accordingly, fermentation processes focused to 4.6 [72], whey proteins are recovered by on the bioconversion of the whole whey, as ultrafiltration [40], lactose is concentrated well as whole whey direct uses, are also and crystallised from whey [64]. Besides, described. some applications concern the non-food uses of fractions containing different com- Finally, the last part of this review deals ponents together, which greatly simplify with the few non-food uses reported for separation steps. This is the case for fer- milk fat, another major milk constituent. mentation of dairy co-products such as whey converted to added value products [97]. 2. MILK PROTEINS The first part of the present review deals with the non-food uses of milk proteins, 2.1. Casein and caseinates i.e. casein and whey protein, in relation to –1 their structural and functional properties. Casein is the main protein (24–29 g·L ) Casein, the major protein in cow’s milk, in bovine milk, as shown in Table I. In fact, has a long history of use in the non-food casein of milk, involved in highly hydrated area. This gaussian coil protein has been , is based on four major compo- α α used since the beginning of the nineteenth nents, s1-casein (38%), s2-casein (10%), β κ century in the manufacture of a wide range -casein (36%) and -casein (13%) and a γ of products including glues [143], rigid minor constituent, -CN (3%). Each con- [26, 101] and textile fibres [44], for stituent varies in composition, example. Compared with casein, whey pro- molecular weight (19 000–23 900), isoelec- tein (about 6 g·L–1, obtained by filtration tric point and hydrophilicity [72, 73]. techniques) historically has found less Acid and caseins are the two numerous non-food applications. A few major types of casein available [72, 118], examples concern the cosmetic and phar- depending on the coagulation process. Non-food applications of milk components 419

Table I. Protein distribution in cow's milk.

Protein Content in g·L–1 Relative proportion in % Casein 25 100 α-Casein 12 48 β-Casein 09 36 κ-Casein 3.25 13 Minor constituents 0.75 3 Whey proteins 5.4 100 β-lactoglobulin 2.70 50 α-lactalbumin 1.20 22 Immunoglobulin 0.25 5 Serum-albumin 0.65 12 Proteoses-peptones 0.60 10

Acid casein refers to precipitated casein, dues, causes them to concentrate at inter- obtained by adjusting skim milk pH to 4.6 faces to form a protein film. This confers with mineral acids such as hydrochloric or upon casein good emulsifying and stabilis- sulphuric acid. Lactic casein is precipitated ing properties. by acidification due to produced Due to their high amount of polar groups, in situ with lactic acid bacteria designed as caseinate also shows good adhesion to dif- a starter. In rennet casein, coagulation is ferent substrates such as wood, glass or obtained by the action of (ren- paper and this hydrophilicity makes casein- net), an which cleaves a chemical ate films excellent barriers to non-polar bond in κ-casein: the casein is substances such as oxygen, carbon dioxide destabilised and forms a three-dimensional and aromas. clot. Water-soluble caseinates can be Chemical modification of casein can obtained by solubilisation of caseins in change protein-protein interactions and alkali media such as sodium-, -, proteins’ interactions with their environ- potassium- or magnesium-hydroxyde, lime ment in order to control specific properties. or [138]. The commercially available Crosslinking agents are difunctional com- sodium caseinate is obtained by dissolution pounds which react with free reactive of acid casein in at a pH groups to make covalent linkage between close to 7. protein chains, leading to the formation of Due to low frequency of secondary a three-dimensional network. Crosslinked structures (α-helix and β-sheets) caseins materials generally exhibit improved phys- are mostly random coil polypeptides with a ical and mechanical properties. high degree of molecular flexibility able to Considering these different properties, form typical intermolecular interactions caseinate-based polymers can be used in (hydrogen, electrostatic and hydrophobic several technical applications such as pro- bonds) [31]. This confers upon caseins tective coating and foams, paper coating, good film-forming and coating abilities or injection moulding dispos- [30, 41, 68]. The strongly amphipatic ables. The specific properties of casein rel- nature of caseins, arising from the balance evant for technical applications are listed of polar and non-polar amino acids resi- in Table II. 420 J.-L. Audic et al.

Table II. Principal technical applications of casein and caseinates.

Product Property Applications Remarks/importance Coating Film forming ability Still used in some Adhesion Ink Still used Technical properties Paper Still used Packaging To be developed finishing Historical Textile coating Historical Good processability Water based glue Historical Bond strength Still used in some few Water resistance obtained applications by crosslinking Plastic Strength Rigid plastic Historical Good mechanical properties Disposable Historical Water resistance obtained by crosslinking Fibre Historical Coating To be developed Film/foil in packa- Laboratory scale ging application Surface tension Emulsifier, detergent Enhancement by chemical Stability of interface modification

2.1.1. Casein as an adhesive to insoluble material; dissociating agents such as ammonia or urea to limit the viscos- According to Tague [143], already in the ity of the adhesive through lowered days of the Egyptians and during the Middle H-bonds between caseinates; sodium sili- Ages, cement and wood glues were made cate to extend working life, tannate or alkali of casein. Casein glues were first manufac- tannate to increase adhesion. tured in the early years of the nineteenth century and mostly used in woodworking Nowadays, casein glues, supplanted by [17]. At the beginning of the twentieth cen- synthetic glues in exterior woodworking, tury, casein glues were formulated for the are still used in labelling adhesives, in the military aeroplane industry (plane struc- bottling industry, in interior woodworking tures were based on wood). A lot of formu- [39] (plywood, door panels, Formica lami- lations for casein-based glues have been nates…), in bonding paper or in pressure published or patented until today [17, 120, sensitive adhesives [124, 126]. 126, 143]: in most cases, casein glues are available as a powder containing two main 2.1.2. Casein as a coating or sizing constituents, i.e. casein and an alkali, agent which are mixed in water before use (less than 24 h). A third mixing chemical In such utilisations, casein acts as a ingredient may also be added according to binder for the coating material, generally a the formulas: lime or copper chloride to mixture of mineral materials, which is give water-resistant glues by promoting applied as a thin layer on the surface of the crosslinking of casein molecules, leading material. Non-food applications of milk components 421

2.1.2.1. Paper industry Such casein coatings promote resistance to abrasion, enhance pigment binding and The hydrophobic/hydrophilic balance of allow the textile to be impervious to mois- casein increases its affinity for pigments, ture when hardened [143]. its ink-binding properties and its adhesion to various substrates. In the paper industry, Because of its film-forming and adhe- casein is used as size for high quality sive abilities, casein size also finds appli- glazed papers or for fine halftone illustra- cation in the textile industry [67]. tions. Caseins combined with acrylates become Water resistance can be achieved by a protective coating against greying of cot- exposure to formaldehyde vapours or by ton [121]. Chemically-modified caseins, dipping in concentrated solutions of for- either grafted with acrylate esters or cross- maldehyde [116]. Formaldehyde or dialde- linked, are used as anti-static finishing of hyde are crosslinking agents which bind natural (wool, cotton and silk) [49] and syn- free amino groups to protein to give a three- thetic (polyester) [165] textile fibres. dimensional network. For example, wall- paper becomes water washable by adding a 2.1.2.3. Leather industry coating of casein solution brushed over Polyol plasticised casein [2] is used in with a solution of formaldehyde. the finishing operations in the leather indus- With high solid contents (china clay, try combined with additional components kaolin, chalk…) coating solutions become such as acrylates [79], phenol derivatives, too viscous, so in some applications, flow pigments for coloured products or binders modifiers are added to enhance the casting such as gelatine or sulfonated castor oil process. Viscosity can be lowered by reduc- [20]. The solution is coated on the leather ing the molecular weight of caseins and before the surface is mechanically proc- by denaturing the protein. This can be essed (brushed, ironed, glazed…) [137]. achieved by addition of urea, by alkaline or enzymatic [100, 127], or by 2.1.3. Casein as a textile fibre disulphide bond reducing agents such as mercaptoacetic acid or 2-mercaptoethanol In 1935, Ferretti patented a process for [119, 148]. Pigments can be directly mixed casein textile called “Lannital®” [44, 52, with the formula to obtain coloured size and 142]. An alkali-solution casein is spinned coatings. into a coagulation bath containing acid (sul- phuric acid) and inorganic salts (aluminium In the middle of the twentieth century, and sodium salts). The spun fibres are insol- paper and board coating accounted for the ubilised by dipping into a formaldehyde major uses of casein [128]. Nowadays solution and water-washed [29, 74, 109]. casein is still used in high quality paper fin- ishing and for enamel grades of paper [107, Casein fibres are known under trade ® ® 162], but a decline in the use of casein in names such as Aralac (USA), Casolana ® paper coating can be mentioned due to (Netherlands) and Fibrolane (UK) [157]. casein’s high costs (about 6 €/kg in 2002). Casein fibres resemble wool and were mostly used during the Second World War, 2.1.2.2. Textile industry generally combined with other artificial or natural fibres such as wool, cotton, viscose Casein was first employed in an way and rayon. Casein polymer fibres have also analogous to that of the paper industry: tex- been grafted with acrylonitrile to give tile fabrics are impregnated with a casein bicomponent fibres [14, 140]. Nowadays, solution and cross-linked either by formal- commercial interest in casein fibres has dehyde vapours or by dipping into a solu- declined, compared with more competitive tion of crosslinker. synthetic fibres [137]. 422 J.-L. Audic et al.

2.1.4. Casein-based packaging films Figure 1 shows a typical stress-strain curve and biomaterials obtained from a tensile test of a plasticised caseinate film and the derived mechanical Transparency, biodegradability and good properties (Tab. III): stress and elongation technical properties (barrier properties for at break, elastic modulus (or Young’s mod- apolar gases such as O and CO ) make 2 2 ulus) and stress at yield. The incorporation casein films innovative materials for pack- of polyol-type plasticizers (glycerol and aging. Nevertheless, casein-based materi- sorbitol) in protein-based films causes a als have two major drawbacks in common decrease in tensile strength and an increase with other protein-based biomaterials: lim- in ultimate elongation. The major differ- ited mechanical properties and water sensi- ence between protein- (casein or whey tivity. protein) based films and synthetic films To overcome weakness and brittleness, (LDPE, HDPE and PVC wrap film) con- plasticisers are added to enhance workabil- cerns elongation at break. The maximum ity, elasticity and flexibility. Plasticisers elongation is rather low in plasticised pro- reduce intermolecular hydrogen bonding tein-based samples (less than 85%) com- while increasing intermolecular spacing. pared with synthetic films (from 150% for By decreasing intermolecular forces, plas- plasticised PVC to 500% for LDPE), which ticisers cause an increase in material flexi- may limit application domains for protein- bility but also a decrease in barrier proper- based films. Compared with starch-based ties due to increasing free volume. To materials, the most commonly used substitute summarise, an initially hard and brittle for synthetic polymers, milk protein-based material becomes soft and flexible when films exhibit better mechanical properties. plasticised enough. The second drawback of caseinate films For casein-based materials the most deals with their water sensitivity and water common plasticisers are polyols, sugars or vapour permeability. Mixing the protein starches owing to their miscibility with the with oils, waxes or acetylated monoglycer- protein and their ability to enhance elastic- ides [23, 24, 78] is an easy route to drasti- ity and flexibility [6, 7, 69, 134–136]. cally reduce water sensitivity. Casein can

Figure 1. Typical stress-strain curve for caseinate-based films. c Young’s modulus; d Tensile strength & stress at yield; e Stress at break; f Elongation at break. Non-food applications of milk components 423 also be hydrophobised by attachment of meability: the degree of binding between hydrophobic ligands, generally alkyl two polymer chains, and conversely, the groups incorporated by esterification or by free volume between two chains. Thus, the using monofunctional aldehydes [9, 22, 78, barrier properties of casein-based films are 87, 102]. Water sensitivity of caseinate strongly modified by additives such as films can also be reduced by crosslinking plasticisers or by chemical modification. with (i) calcium [9, 115]; (ii) trans- To overcome the problem of environ- glutaminase [66, 84, 98]; (iii) γ -irradiation mental pollution by synthetic polymers and [16, 96, 115]; and (iv) formaldehyde or with regard to their specific properties, dialdehydes [62, 80]. On the other hand, the protein-based biopolymers have gained resulting three-dimensional casein network growing interest in the last decade and gives a rigid material with both a higher represent an emerging field [39]. Casein- Young’s modulus and tensile strength and based films and biomaterials obtained from with reduced elongation at break than plas- caseinates can find many applications in ticised casein. packaging [72, 73, 78], in edible films and As for other proteic materials, casein- coatings for fruits and vegetables [12, 22, based films are hydrophilic, making them 78] or in mulching films [39]. Neverthe- excellent gas barriers to non-polar sub- less, research on the technical alternative stances such as oxygen, carbon dioxide and uses of protein has been limited so far com- aromas. As a general trend, barrier proper- pared with some other common biopoly- ties of polymers depend on polymer struc- mers, especially starches. The higher cost ture and its segmental mobility, which of casein compared with common polysac- influences its mass transport properties. charides could be compensated for by Therefore, two main factors control its per- the best properties and performances of

Table III. Comparison of tensile strength and elongation at break of natural and synthetic packaging films.

Film Tensile strengtha Elongation at break Ref. (MPa) (%) NaCAS/Glycerol (4:1)b 17.4–26.7 10.5 [134] NaCAS/Glycerol (2:1) 10.9–11.7 73.7–84.2 [134] NaCAS/PEG (4.54:1) 10.9–16.35 5.3 [134] NaCAS/PEG (1.9:1) 10.9–13.9 25.4 [134] WPI/Glycerol (5.7/1) 29.1 4.1 [90, 91] WPI/Glycerol (2.3/1) 13.9 30.8 [90, 91] WPI/Sorbitol (2.3/1) 14.0 1.6 [90, 91] WPI/sorbitol (1/1) 14.7 8.7 [90, 91] Starch/Glycerol (2.52/1) 17.2 10.8 [7] LDPE 13.0 500 [91] HDPE 26.0 300 [91] Plasticized PVC 15.0–30.0 150–350 This work (wrap film) NaCAS: sodium caseinate; PEG: polyethylene glycol; WPI: whey protein isolate; LDPE: low density polyethylene; HDPE: high density polyethylene. a Test conditions: 23 °C temperature, 50% relative humidity (RH); b ratio in parentheses refers to the weight ratio of protein to plasticiser. 424 J.-L. Audic et al. protein-based biomaterials. For non-food 2.1.6.2. Concrete and cement applications, casein issued from waste For its adhesive and emulsifying prop- streams should be a convenient way to save erties, caseinate is used (or claimed so) in costs. concrete formulation in Eastern Europe, as well as cement, asphalt and bitumen [106, 2.1.5. Rigid casein plastics 110, 138]. Rigid plastic based on rennet casein is one of the best-known examples of non- 2.1.6.3. Cosmetics food application for milk protein [138, Caseinate is used as surface active agent 143]. Rennet casein and fillers are mixed in soaps [1] and various cosmetics such as with 20–35% water before being mechani- cold wave lotions, hair sprays and hand cally processed by high pressure extrusion [125]. Casein hydrolysates could into plastic goods, which are cured for a also be active substances for skin hydration period of several days in a dilute solution of [27]. However, little information is availa- formaldehyde [26, 101, 111]. Any suitable ble about these applications and their mar- pigment or colouring matter can be added. kets, which seem rather limited. Casein plastic was first available in France and Germany under the trade name of “Galalith®” in the early twentieth century 2.1.6.4. Other industrial applications but other casein plastics have been patented Casein presents good metal- and - under the trade names of Erinoid® (UK), binding properties, making it suitable for Aladdinite® (USA), Casolith® (Netherlands), absorbing and recovering chromate in Lactoloid® (Japan) and Lactolithe® (France). wastes from manufacturing processes such The importance of casein plastics has now as electroplating [36, 37] and water purifi- declined due to severe competition from cation [155]. In rubber products, casein has synthetic plastics with better properties. been used as a reinforcing agent and stabi- Although casein plastics are still manufac- liser in rubber tyres [42, 54]. Casein and tured today into buttons, buckles and imita- caseinate are also used in several other non- tion-ivory knife handle, the range of articles food applications such as dish-washing liq- is becoming more and more limited com- uids [1, 114, 156]. pared with the increasing number of articles made of synthetic plastics. 2.2. Whey proteins 2.1.6. Casein as an additive Whey proteins, 15 to 22% of the total milk proteins, are generally separated from Considering their amphipatic nature, whey by a membrane process as whey pro- caseins are often used as emulsifiers or sta- tein concentrates (WPC) or whey protein bilisers in numerous formulations where isolates (WPI) [40, 50, 164]. WPC have a casein does not constitute the major constit- protein content ranging from 30 to 90% uant. [77] while WPI contains more than 90% protein in the dry matter. The two most 2.1.6.1. Paints abundant proteins in whey are β-lactoglob- Because of its solubility and ability to ulin and α-lactalbumin as shown in bind pigments, caseinate has found appli- Table I. Most of the non-food uses of whey cations in water-based paints [46, 130, proteins deal with specific properties of 154]. Caseinate’s emulsifying properties single proteins used in cosmetology and make it a good stabiliser and emulsifier in pharmacology [75]. β-lactoglobulin and oil and latex paints. Its content in such for- α-lactalbumin are used as hydrating and anti- mulas does not exceed 1 to 2% [53, 123, wrinkle agents [27]. Lactoferrin can pre- 124]. vent formation of free radicals through its Non-food applications of milk components 425 iron-chelating property [27]. In the 90s, glucose, free hydroxyl groups and carbon- whey proteins were also employed as an carbon bonds) that can be chemically or antianemic preparation in the form of iron enzymatically modified. proteinate [33]. The major uses of lactose include food There is an increasing economical and ingredient, ingredient in infant formulae, environmental need for finding new appli- filler or coating agent for tablets in the cations for whey proteins [117]. The phys- pharmaceutical industry, raw material for ical and functional properties of whey lactose derivatives and substrate for fer- proteins to be outlined are: solubility, vis- mentation. However, lactose finds some- cosity, cohesion and adhesion, emulsifying what limited application in food products properties, water sorption and gel-forming because of its low digestibility and poor properties [76]. For example, the film- solubility (ability to crystallise) [61, 64, forming ability of whey proteins has been 161]. Accordingly, the food industry only used for the production of protective films uses a small part of the lactose produced and coatings [28, 90–92]. The mechanical each year, making lactose non-food appli- and physical properties of whey protein- cations of prime interest. Considering the based material are improved by plasticisa- high biological oxygen demand of lactose tion [90–92] (Tab. III) and/or crosslinking [88] (BOD about 35–45 mg per litre of [82]. Whey proteins are also used in paper whey) the dairy industry needs to discover coating to provide good appearance, print- uses for lactose as well as for whey itself in ability and low water vapour permeability order to dispose of these co-products in [59]. Because of their natural origin and some environmentally acceptable way. emulsifying properties, whey proteins Several valuable products from lactose are used as substitutes for synthetic sur- have then been proposed in order to reduce factants in the formulation of non-aggres- the huge amounts of dairy effluents. sive and shampoos. Whey protein Most of the non-food uses deal with fer- hydrolysates have also been used in cosme- mentation of whole whey (review in a fol- tology (shampoos and hair creams) and lowing section; Fig. 2). Other non-food pharmacology [58, 63, 75]. uses of lactose include raw material for lactose derivatives, pharmaceutical and cosmetic formulations [64]. For pharma- ceuticals, raw lactose is mostly used as a 3. LACTOSE filler, drug carrier and coating agent to cover tablets. Lactose has also been pro- Lactose is the characteristic carbohy- posed as an inducer for overexpression of drate of bovine milk, present at approxi- protein in genetically engineered organ- mately 4.8% (wt/vol) [161]. The major part isms [103]. of lactose produced each year is recovered from whey (Fig. 2). The pure lactose recov- 3.1. Derivatives of lactose by chemical ery process generally involves concentra- and enzymatic modification tion by evaporation, crystallisation, separa- tion, refining, drying and milling. The use of lactose as a raw material in Because of its physical, chemical and the chemical industry has been reviewed in functional properties, lactose, which is a detail by Zadow [163] and Thelwall [145]. disaccharide of glucose and galactose, is Although the chemistry of lactose has used to produce some derivatives. The milk made rapid progress over the past 30 years, sugar contains a number of reactive sites the use of lactose as a chemical feedstock (glycosidic linkages, reducing group of is only now being fully considered. 426 J.-L. Audic et al.

Figure 2. Utilisations of whey (SCP: Single cell protein and WPC: whey protein concentrate).

The lactose derivatives of great interest for group of lactose. It finds applications as applications in the non-food area are [64]: a gel-firming agent and in the composi- tion of the preservation solution for – lactulose [93], an isomer of lactose pro- organs prior to transplantation; duced by alkali hydroxide catalysis and widely used in pharmaceuticals (laxa- – lactosyl urea obtained by reaction of tive) or as a growth promoter for pigs lactose with urea, described as a poten- and calves [60, 161]; tial feedstock for ruminants because of increased palatability and reduced tox- – lactitol [60, 122], issued from reduction icity [163]. of lactose, is used as a raw material for Other lactose derivatives of commercial ester emulsifiers manufacture. These interest such as galacto-oligosaccharides or excellent are used in deter- hydrolysed lactose syrup are mostly used gents, surface modifiers and emulsifi- in the food industry [61, 161]. New lactose ers. Lactitol also finds application in derivatives have also been described humectants, plasticisers, lacquer addi- such as esters, halogenated derivatives, lac- tives and hot melt additive adhesives tosyl halides, lactosides, anhydro derivatives, [145]; cyclic acetal derivatives, deoxy derivatives, – lactobionic acid [60], obtained by cata- nitrogen-containing derivatives and unsatu- lytic oxidation of the free aldehyde rated derivatives. Non-food applications of milk components 427

Some other attempts have been made However, lactose hydrolysis is often a to valorise lactose from whey permeate step prior to fermentation (Fig. 2): micro- obtained by ultrafiltration (UF) techniques organisms, unable to ferment lactose, are and corresponding to a deproteinated whey able to ferment hydrolysed lactose, allow- (Fig. 2). Such an UF whey permeate is used ing a wide variety of fermentation prod- in the formulation of phenol-formaldehyde ucts. For most of the processes, lactose resins such as plywood adhesives [150– hydrolysis involves an increase in the proc- 152]: up to 50% weight substitution of phe- ess costs. Hydrolysis of the β-glycosidic nol by a whey permeate-based modifier can bond into glucose and galactose can be be reached without significant loss of prop- performed with either such as erties. Whey permeate is also used for β-D-galactosidase (lactase) or acid cataly- the preparation of special polyurethane sis [55, 64, 76, 97]. Hydrolysis processes foams [153], lactose working as the chain developed from pilot to industrial scale extender in the place of polyols. have been reviewed by Axelson and Zacchi [10] with respect to their economic 3.2. Fermented products feasibility. In whole whey fermentations, from lactose/whey soluble proteins bring a part of the nitrogen Whey is the main source of lactose source needed for the development of (Fig. 2) and most of the non-food applica- microorganisms. However, in most proc- tions proposed for lactose concern direct esses dealing with whole whey fermenta- fermentation of whole whey [64, 71, 97, tion, it is necessary to have an extra nitrogen 163]. Whey is composed of mainly water source or to hydrolyse whey protein to (about 93%), lactose (4.9 to 5.1%), soluble achieve good growth and productivity. proteins (0.9 to 1%), ash (0.5 to 0.7%), fat (0.1 to 0.3%) and lactic acid (0 to 0.2%) 3.2.1. Methane production [76]. To make 1 kg of cheese, approxi- by anaerobic digestion mately 9 kg of whey is generated [55, 77] and world cheese production generates The production of methane or biogas via more than 145 × 106 t of liquid whey per fermentation of whey is a process com- year, of which 6 × 106 t is lactose. Fermen- posed of three successive steps: lactose tation can thus be a solution to give added (and protein) hydrolysis, fermentation and value to cheese whey that could otherwise methanogenesis [141]. This complex proc- be disposed of as a waste stream generating ess involves several mixed bacterial spe- high BOD. Fermentation thus also contrib- cies. According to Figure 3, the methano- utes to the reduction in dairy waste streams. genic process converts around 90% of A wide range of products, summarised hydrolysed organic matter to biogas: CH4 in Table IV, can be obtained from lactose and CO2 [5]. Methane production via cheese or whey fermentation [48, 55, 56, 64, 76, whey anaerobic fermentation should thus 89]. According to Atkinson and Mavituna represent an important source of energy as [8] they are classified into 3 categories: fuel or to generate electricity: theoretically, 1 kg of lactose yields 0.75 m3 of biogas con- (i) high volume – low value: methane, eth- taining approximately 50% vol/vol meth- anol, biomass, animal feed, water puri- ane [64]. For a deproteinated milk whey the fication, effluent and waste treatment; theoretical yield is approximately 20.7 m3 (ii) high volume – intermediate value: methane/m3 (equivalent to 18.6 L of fuel amino acids, organic acids, food prod- oil) [64, 76]. But it is compulsory to over- ucts, Baker’s yeast and biopolymers; come some problems specific to anaerobic (iii) low volume – high value: antibiotics, digestion to reach these theoretical yields: health care products, enzymes and vita- the process may be slow to initiate, a long mins. residence time is required and waste 428 J.-L. Audic et al.

Table IV. Whey/lactose fermentations.

Product Organism Comment Ref. Yeast Single cell protein Kluyveromyces fragilis Commercial process [19, 21, 32, 50, Kluyveromyces lactis 55, 71, 77, 88, 95, Baker’s yeast 99, 129, 132, 139] Saccharomyces cerevisiae via lactic acid or hydrolysed lactose Solvents Ethanol Kluyveromyces fragilis [11, 13, 21, 50, Candida pseudotropicalis Commercial process 51, 55, 64, 81, 89, Butanol Zymomonas 99, 104, 108, 113, 133, 147, 162] Clostridium acetobutylicum Commercial process Clostridium butyricum butanol, acetone, methanol [71, 86] Biogas [5, 25, 64, 76, 94, Methane Mixed population Anaerobic fermentation 141, 158] of anaerobic bacterias Commercial process Organic acids Lactic Lactic acid bacteria Commercial process Candida

Citric Aspergilus niger via pyruvate or from acid permeate [3, 15, 34, 35, 56, 64, 65, 144, 162] Acetic Acetobacter Commercial process Clostridium thermoaceticum

Lactobionic Pseudomonas sp. Aspergillus terreus Itaconic Commercial process Polysaccharides Xanthan Xanthomonas campestris Commercial process Adapted strain of Exoheteropolysaccharide X. campestris Pullulan

Dextran Leuconostoc mesenteroides [45, 47, 105, 112, 131, 146] Phosphomannan Hansenula sp.

Gellan Pseudomonas elodea

Others Streptococcus thermophilus, S. cremoris, S. lactis, Lactobacillus bulgaricus… Other biochemicals Vitamins Propionibacterium sp. Vit. B12 [55, 64]

2-3 butandiol Bacillus polymyxa [133]

Oils High C/N ratios [38] Non-food applications of milk components 429

Figure 3. Anaerobic digestion of organic material, from [5].

streams of high BOD [141] are generated observed [88] with a yield of dried yeast of during fermentation. In consequence, the 50% of the weight of the lactose used [55]. effluents generated by anaerobic processes are not suitable for pouring into water 3.2.3. Alcohol production streams and post-treatments are required to reduce residual BOD. Several kinds of Developments in whole whey utilisation anaerobic digesters incorporating cell recy- also focused on the production of alcohols cling or cell immobilisation have been stud- (mainly ethanol) [13, 51, 81, 89, 108]. High ied [5, 25, 94, 141, 158] and the develop- ethanol yields (about 80%) can be reached ment of the anaerobic process will depend from adapted Kluyveromyces fragilis on its economic feasibility. strains. Ethanol can then be further used as an energy source (as fuel) or to produce 3.2.2. Single cell protein production vinegar or acetic acid. Several distilleries (SCP) produce ethanol from whey in Ireland, the USA and New Zealand where about 50% The use of lactose or whey as a carbon of cheese whey production is fermented to source for the production of yeast biomass ethanol [55, 89]. Cheese whey generally is a simple treatment process for increasing contains carbon and nitrogen substrates the value of food industry co-products [32, (vitamins, fatty acids and sterols) required 50, 71, 88, 132]. Several plants producing for microorganism growth. Lactose is first microbial biomass from cheese whey have hydrolysed by β-galactosidase (from a been reported in France, the USA, Germany micro-organism) and the resulting mixture and Australia with two major processes of glucose and galactose is then used as the known as the Bel Fromageries process and carbon source by Saccharomyces cerevi- the Vienna process. If complete consump- siae [11, 21]. tion of lactose is to be achieved it is neces- Different processes based on continuous sary to add nitrogen and phosphorous [77]. fermentation with cell immobilisation or Biomass produced from both batch and cell recycling [64, 99, 104, 133, 147, 159] continuous processes [19, 21, 88, 95, 99, have been explored for production of etha- 129, 139] is mostly used as animal feed nol. A recent alternative is to use recom- supplement but also in production of binant yeast grown directly on cheese baker’s yeast. These processes are also of whey, allowing high yield of ethanol [113]. prime interest in dairy wastewater treat- A mixture of acetone, butanol and ethanol ment: over 80% reduction in wastewater (3/6/1:v/v) [71] can be obtained by fermen- biological oxygen demand (BOD) has been tation of whey [71, 86], but the commercial 430 J.-L. Audic et al. potential of the technique seems low at the gum is an heteropolysaccharide produced present time. 2–3 butanediol produced by by Xanthomonas campestris [105, 146]. fermentation of cheese whey has potential Whey lactose has been widely used for the use in the chemical industry and as alterna- production of a large range of exopolysac- tive energy source [133]. charides [45, 47, 64, 112]: dextrans (Leu- conostoc mesenteroides), phosphomannans 3.2.4. Other fermented bioproducts (Hansenula sp.), gellans (Pseudomonas elodea), pullulans (Aerobasidium pullu- 3.2.4.1. Organic acids lans), and several heteropolysaccharides (Streptococcus thermophilus, S. cremoris, Acetic, propionic, lactic, lactobionic, S. lactis, Lactobacilus bulgaricus and citric, gluconic and itaconic acids can be L. pastorianus). obtained from lactose/whey fermentation [3, 15, 34, 35, 56, 64, 65, 144, 159]. Most Adapted micro-organisms and proc- of them find applications in speciality esses can produce several different vita- chemicals. For example, lactic acid can be mins and amino acids from lactose whey used to produce propylene oxide, biode- fermentation [55, 64]. gradable polylactic acid polymers, propyl- Among the most valuable products, ene glycol or acrylic fibres, making the lac- exopolysaccharides ($ 11 to 17.6/kg), cal- tic acid market of prime importance (about cium propionate ($ 4.4/kg), lactic acid 27 million kg per year) [83, 85, 159]. ($ 2.2/kg) and potassium acetate ($ 1.06/L) Recent interest in biodegradable polymer are obtained with good yields and present a could lead to enhanced demand for lactic potentially large market (Tab. V). Methane acid. Acetic acid can also be selected as a may also represent an interesting energy raw material in the chemical industry for source for direct use on-site. It must be kept example to produce calcium magnesium in mind that the prices of these products are acetate (CMA) used in large amounts as useful only for comparison between each road or airport de-icer [159, 160]. Propi- other and prices could vary in a relatively onic acid is used in the production of feed short time. For example, lactose price and food additives, herbicides and chemi- dropped from $ 0.6/kg to $ 0.3/kg during cal intermediates [64]. the last six months of 2002, depending on whey surplus. For lactic acid, the current 3.2.4.2. Oils worldwide production is estimated to be 40 000 t per year and the price is estimated Production of lipids by special yeast at about $ 2/kg. Currently, xanthan gum under high C/N ratios has been explored as still costs about $ 11–12/kg. an alternative source of oil for countries with poor domestic vegetable oils produc- tion (New Zealand) [38]. 4. MILK FAT

3.2.4.3. Exopolysaccharides Milk fat includes mono-, di- and triglyc- Extracellular microbial polysaccharides erides, fatty acids, cholesterol, milk fat are mostly used as thickeners, emulsifiers globule membrane and phospholipids. and stabilisers in the food industry, but also According to Kaylegian [70] very few non- in the textile industry [64, 76]. Whey per- food uses of milk fat have been proposed meate is used as a substrate for the produc- until now. Nevertheless, antimicrobial, anti- tion of polysaccharides by fermentation oxidant and anticarcinogenic properties have [131], but lactose needs to be first hydro- been attributed to lauric acid and conju- lysed before being fermented by commer- gated linoleic acid, both fatty acids recovered cial bacterial strains. For example, xanthan from milk fat. With respect to its emollient Non-food applications of milk components 431

Table V. Comparison of various products from 50 000 kg of whey permeate (5% lactose) ([159] with permission).

Product Quantity Unit price Value Use Market and $ $ production Lactose 1500 kg 0.44/kg 660 Food, pharmaceutical 95 000 t/yr Methane 780 m3 0.176/m3 138 Energy On-site use Ethanol 1340 L 0.40/L 536 Fuel Large CaMg-acetate 3000 kg 0.66/kg 1980 Road deicer < 10 000 t/yr potentially large K-acetate 6250 L 1.06/L 6 625 Airport runway deicer ~20 × 106 L/yr Lactic acid 2250 kg 2.2/kg 4950 Food, chemical and ~30 × 106 kg/yr polylactides potentially large Ca-propionate 1500 kg 4.4/kg 6600 Natural food preservative Small but good Xanthan gum 1750 kg 11/kg 19 250 Food thickener ~20 × 106 kg/yr Transgalactosylated 1250 kg 17.6/kg 22 000 Food, pharmaceutical 6000 t/yr oligosaccharides potentially large properties, milk fat is claimed to be used in compliance with environmental regula- cosmetics in the manufacture of skin care tions. The process water of dairy effluents creams and shampoo [4, 70]. Another (excluding cleaning in place steps with example is the conversion of surplus milk chemical cleaning agents) is mainly com- fat into more profitable products: (i) fatty posed of diluted milk and whey in a ratio acids, diglycerides and monoglycerides depending on the type of product (cheese, obtained by lipase-catalysed glycerolysis powder, milk…) of the plant. At the present of milk fat [18], and (ii) flavouring agents time part of these fluids are discarded in and detergents. The emulsifying properties sewer systems [89, 161] or directly used of whey can be improved by addition of without treatment (Fig. 2): mono- and diglycerides issued from milk – as animal feed [89, 97, 159]. Whey rep- fat hydrolysis. However, in most of the non- resents a source of protein, lactose and food applications, milk fat is used as a fatty minerals. For example, ruminants can acid reservoir to produce mono- and diglyc- take 30% of their dry matter require- erides that are mostly used in the manufac- ments from liquid whey; ture of emulsifiers. – as agricultural fertiliser [89, 97, 159, Milk fat has been proposed for the man- 161], with two important drawbacks: ufacture of edible and packaging films and transport becomes very expensive due protective coatings [43, 57]. Films made to the volume when whey is not concen- from milk fat or milk fat fractions exhibit trated enough and whey leaves saline low gas and water vapour permeability and deposits on soils. improved hydrophobic properties [149]. Nevertheless, these ways of consump- tion of dairy effluents should be compro- mised by future requirements for safety 5. DAIRY EFFLUENTS and compliance with environmental regu- Besides whey surplus, non-food uses lations. can also be an alternative approach to give Within the frame of clean, sober and cost- added value to industrial dairy effluents in effective processes, the above-mentioned 432 J.-L. Audic et al. non-food applications should be applied to and soluble protein), coatings, films and effluents. A first way is to concentrate efflu- packaging are of great interest in the field ents by appropriate techniques (membrane of biodegradable and environmentally- process, evaporation…) in order to obtain friendly polymers/materials. a solution able to be used in the target appli- Lactose is used as a raw material for the cation. Fermentation appears to be the best manufacture of derivatives such as lactitol, way to give added value to such concen- lactulose or lactobionic acid. Nevertheless, trated fluids through production of valuable most of the non-food uses deal with the fer- compounds such as alcohol or exopolysac- mentation process of lactose providing a charides. A second route, more restrictive, wide range of valuable products such as is to perform a selective recovery of an indi- methane, alcohols, organic acids, baker’s vidual component (such as casein obtained yeast, vitamins or exopolysaccharides. Fer- by precipitation) in order to use it in the above-mentioned non-food applications. mentation of (hydrolysed) lactose from The cost of effluent treatment combined whey permeate or whole whey is an alter- with the negligeable value of lost com- native way to contribute to the reduction in pounds is expected to be lower than the dairy waste streams. added value of non-food applications and Concerning milk fat, currently only a the saving on treatment of sewer systems. few non-food applications have been devel- oped such as milk fat-based emollients or fatty acid production, but the commercial 6. CONCLUSION potential seems to be promising. Losses of milk fat are reduced compared with other This review constitutes a survey of cur- components because it is the most valuable rent and potential non-food applications of component in food applications. 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