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CASEIN AND CASEINATES/Methods of Manufacture 943

Straub O (1987) In: Pfander H (ed.) Key to Carotenoids.Basel: Birkhauser.

Subcommittees on Upper Reference Levels of Nutrients andInterpretation and Uses of Dietary Reference Intakes,and the Standing Committee on Scientific Evaluationof Dietary Reference Intakes (2000) Dietary ReferenceIntakes for Vitamin C, Vitamin E, Selenium and

CASEIN AND CASEINATES

Contents

Methods of Manufacture

Uses in the Food Industry

Methods of ManufactureC R Southward, Fonterra Research Centre,Palmerston North, New Zealand

This article is reproduced from Encyclopedia of Dairy Sciences,

Copyright 2002, Academic Press.

Introduction

The commercial production of casein, the principalprotein in cows’ milk, has occurred for most of the20th century. During the period to 1960, the majorproportion of casein was used in technical (or non-food) applications. More recently, however, there hasbeen a significant change from technical to edible usesfor casein products and this has been reflected in theintroduction of requirements for pasteurization ofmilk intended for casein manufacture (c. 1970) andthe greater number of specifications for microbialquality and freedom from impurities. At the presenttime, the major producers of casein include the Euro-pean Community (in particular, Denmark, France,Germany, the Irish Republic, and The Netherlands)and New Zealand, with Poland, Australia, and Indiaproducing smaller quantities. World production ofcasein products is currently estimated at 220 000–250 000 tonnes. This article describes the manufac-ture of the main casein products.

General

The proteins that exist in milk can be broadly dividedinto two groups – casein and whey proteins. Caseinsmay be considered as those proteins that are precipi-tated when unheated (raw) milk is acidified to pH 4.6

Carotenoids: A Report of the Panel on Dietary Antioxi-dants and Related Compounds. National AcademyPress, Washington, D.C.

Von Lintig J and Wyss A (2001) Molecular analysis ofvitamin A formation: cloning and characterizationof beta-carotene 15,150-dioxygenase. Archives of Bio-chemistry and Biophysics 385: 47–52.

(the isoelectric point of casein) whereas whey proteinsremain in solution. Commercial casein is a mixture offour different caseins – as1-, as2-, b- and k-casein, andmay sometimes be referred to as whole casein. As aphosphoprotein, casein belongs to a relatively rareclass of proteins. It contains 0.7–0.9% phosphorus,covalently bound to the casein by a serine esterlinkage. Casein exists in milk in combination withcalcium, inorganic phosphate, and citrate as a col-loidal suspension of complex micelles and accountsfor 2.6–2.9% by weight of whole milk.

Manufacture

0003Casein may be precipitated from skimmed milk toproduce several products such as acid casein, rennetcasein, or coprecipitate. All these products areinsoluble in water after precipitation. However,addition of alkali to acid casein yields water-solublecaseinate.

Acid Casein

Acidification

0004When milk (pH 6.6) is acidified, the calcium andinorganic phosphate are removed from the caseinmicelles, the net charge on the micelles decreases,and the micelles become less and less stable until thecasein precipitates. Complete precipitation of thecasein occurs at the isoelectric point, pH 4.6. Acidifi-cation of the milk may be carried out by one of thefollowing processes:

1. 0005Inoculation of milk with lactic acid-producingbacteria such as Lactococcus lactis subsp. lactis

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944 CASEIN AND CASEINATES/Methods of Manufacture

or cremoris. These bacteria, commonly known as‘starters,’ convert some of the lactose in the milkto lactic acid during the period of incubation(about 16–18 h). This is the most commonlyemployed method of manufacture in New Zealand(Figure 1).

2. Direct addition of dilute acid to skimmed milk.Hydrochloric acid, sulfuric acid, phosphoric acid,or lactic acid (or, occasionally, other organic acids)may be used for this purpose. The most commonmethod of producing acid casein in countries otherthan New Zealand is by means of hydrochloricacid.

3. Indirect acidification of skim milk. A number ofalternative processes have been patented in whichskimmed milk is acidified by one or more of thefollowing:. contact by means of ion exchange resins in the

acid (cation) form. addition of acidified whey. electrodialysis

It is believed that these processes have relativelyminor commercial significance.

Cooking/Acidulation

In the manufacture of acid casein, acidification of themilk is followed, or occasionally preceded, by heatingof the mixture. Heating promotes agglomeration ofthe casein curd particles which subsequently shrink(syneresis) to expel whey. At the same time, the curdsbecome firmer and are able to withstand the mechan-ical processing that follows. Heating of the acidifiedmilk is sometimes termed ‘cooking’ (as used in cheesemanufacture) and may be carried out, usually in thetemperature range 45–55 �C, by:

1. injection of steam into the pipeline carrying theacidified milk

2. indirect heating by means of a heat exchanger3. a combination of both – preheating through a heat

exchanger with steam injection to complete theheating process (Figure 1)

In each case, the cooked curds and whey are held in a‘cooking pipe’ for a period of about 10–20 s beforethey emerge into an acidulation vat. The curds andwhey may remain here for a period varying from 30 sto about 15 min, during which time the curds areagitated gently in the whey until equilibrium betweenthe calcium in the curds and that in the whey isattained.

Alternative processes may use a syneresis tube; thecooked curds and whey are held in a large-diametertube for a period of several minutes (also undergoingacidulation or equilibration).

Dewheying and Washing

Following acidulation, the curds and whey aredischarged by gravity to a dewheying screen abovethe first washing vat. The whey is removed and thecurds fall into the vat. Alternatively, the curds andwhey may be separated more completely using a hori-zontal solid-bowl centrifuge (decanter) or a casein-dewatering press before the curds are transferred tothe first wash. A combination of screening and decanterdewheying can be used to reduce the hydraulic load onthe decanter. The purpose of washing is to removewhey (containing mainly lactose) from the curds sothat the casein produced is relatively pure. The tem-perature of the wash water may be varied, dependingupon particular requirements. Casein is usually sub-jected to multiple washes and these are operated in acounterflow to the direction of the curds, with thepurest curd meeting the cleanest water.

Dewatering

After washing, the curds are mechanically dewateredto remove excess water before drying. As drying is arelatively expensive operation, it is worthwhile re-moving as much water as possible from the curdbefore transferring the casein to the drier. The textureof the curd is affected by temperature; as the tempera-ture of the wash water is increased, the curd releasesmore water during dewatering but becomes firm andmore plastic and is consequently harder to break upand dry. Therefore, it is necessary to regulate carefullythe temperature of the last wash to optimize the con-flicting requirements of minimum water content andmaximum friability of the curd.

Equipment for dewatering casein curd consists ofroller or belt presses, decanters, and screen-bowl cen-trifuges. The roller press, used for many years, isdesigned to reduce the moisture content of curd toabout 55%. The belt press will do a similar duty.Solid-bowl decanters or screen-bowl centrifuges arecapable of reducing the moisture content of acidcasein curd to about 52%.

Drying

Drying of casein curd is most commonly carried outusing horizontal vibrating fluid-bed driers. Thesedriers have two or more perforated stainless-steeldecks (Figure 1). The combined effect of vibrationof the decks and the flow of hot air (typical tempera-ture range 75–115 �C) up through the holes in thedecks causes the casein curd to become fluidized andmaterially helps in the removal of moisture from theparticles. Most of the water is removed duringthe early stages of drying of the casein as it is evapor-ated from the surface of the particles. The later stages

Tankerreception

Whole milk storage

Wm

Unloading Pasteurizer

Preheater

Steam injector

Cas

ScreenAcidulationWashing and

separation by screening

Cas

Cas

Press

Casein drier

Fines recoverycyclone

WheyExhaust

Tempering

Roller mill

Oversizeparticles

Cas

Blending80

mes

h

60 m

esh

30 m

esh

Sifter

Metalremoval

Storage silos

Bag-fillinghopper

BagsewingMetal

detectorPalletized bagsto store

Bagflattening

Weighing

Coagulation silos

Separator Sm

Sm

Sm

Co

Co

Flowcontrol

Startervessels

Cream

WmHoldingtubes

fig0001 Figure 1 Outline of the manufacturing steps involved in producing lactic acid casein from skim milk. Wm, whole milk; Sm, skimmed

milk; Co, coagulum; Cas, casein.

CASEIN AND CASEINATES/Methods of Manufacture 945

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946 CASEIN AND CASEINATES/Methods of Manufacture

of drying require the transfer of moisture from thecenter to the surface of the particle, and this is a muchslower process.

Pneumatic-conveying ring driers and attritiondriers are also used for drying casein. These employinline milling and tend to produce finer caseinproducts than those dried in fluid-bed driers.

Cooling, Tempering, Milling, Sifting, Blending,Packing

Casein that is produced using fluid-bed driers is warmand soft and unsuitable for grinding immediately insome mills such as roller mills. Consequently, thecasein may be cooled and then transferred totempering bins where equilibration of moisture canoccur in and between all the particles during a periodof 8–24 h.

The casein may then be ground and sieved,using multideck, gyrating screens, into various par-ticle sizes, usually < 600 mm. Very fine casein (e.g.< 150 mm) is generally produced using pin mills.

Following blending of the ground casein, it ispacked into multiwall paper bags equipped withplastic liners and stored. The typical composition ofacid casein is shown in Table 1.

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Rennet Casein

Action of Chymosin

Casein may also be precipitated from milk by theaction of a proteolytic enzyme, such as chymosin,which is present in calf rennet. Chymosin (and otherenzymes from animal or microbial sources that causemilk to clot) splits off a portion of the k-casein (re-ferred to as glycomacropeptide or GMP) from themicelles. As a result, the micelles are no longer

Table 1 Typical composition and properties of casein products

Component Acidcasein

Composition Amount per 100 g

Moisture (g) 11.5

Fat (g) 1.1

Protein (g) (nitrogen � 6.38) 86.2

Ash (g) 1.8

Lactose (g) 0.1

Amount per 1 kg

Copper (mg) 2

Lead (mg) <1

Iron (mg) 5–20

Physical propertiesColor Creamy white

Flavor Bland, clean

Solubility in water Insoluble

stable in the presence of calcium ions and form athree-dimensional gel. This process is essential in theproduction of most types of cheese.

Clotting of Skimmed Milk

Pasteurized skimmed milk at a temperature of 29 �C(or lower) is mixed with calf rennet (or other milk-clotting enzyme) in the approximate ratio (byvolume) of 1:7500 rennet to the milk. If a lowersetting temperature is used, renneting time must becorrespondingly increased. It is also possible toreduce the quantity of rennet added under these con-ditions and consequently allow a longer time forrennet action to occur.

Cooking

The usual technique for cooking rennet casein in-volves the injection of steam into a cooking line ofclotted milk pumped from a vat. However, the vatcooking technique (similar to that used in cheesemanufacture) is also practiced in some countries.The cooking temperature used in making rennetcasein usually varies from about 50 to 60 �C.

Dewheying, washing, dewatering, and drying ofthe curd then proceed in a manner similar to thatused for acid casein, and the dried casein is alsotreated as outlined previously.

Where indirect cooking of rennet casein is used, atubular heat exchanger may be used to cook the curdsand whey to a temperature similar to that used in thedirect cook (steam injection) process. Other process-ing steps are similar to those described above but noacidulation step is required after cooking of therennet casein.

The typical composition of rennet casein is shownin Table 1.

Rennetcasein Sodiumcaseinate (spraydried)

11.5 4.5

0.4 1.0

81.3 92.0

8.2 3.6

0.1 0.1

2 2

<1 <1

5 5–10

Creamy white White

Bland, clean Bland, clean

Insoluble Soluble

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fig0002

CASEIN AND CASEINATES/Methods of Manufacture 947

Coprecipitates

Coprecipitates are combinations of casein and wheyproteins that are coprecipitated from heated (skimmed)milk. When milk is heated to a temperature greaterthan 70 �C, some of the whey proteins are heat-denatured and may interact with some of the caseins.When a casein precipitant (such as acid or calciumchloride) is added to the heated milk, the casein andwhey proteins coprecipitate together. Depending on thepH of precipitation (which may vary from 6.6 to 4.5),the coprecipitate will contain different quantities ofcalcium (high-calcium at pH 6.6 to low-calcium atpH 4.5). As whey proteins have a higher nutritionalvalue than casein (as measured by several differentbiological and chemical techniques), coprecipitatesalso have an enhanced nutritional value comparedwith casein. The yield of coprecipitate from skimmedmilk is usually 5–20% greater than that of acid casein.

Caseinates

Caseinates are produced by the neutralization of acidcasein with alkali. All caseinates are substantially

Casein dewatering

Casein mincer

Sodium hydroxide

Curd−alkali mixerDC

Colloidmill

Water(40 8C)

F1pH

Jacketed vats

Hot w

To spray drier

Sodium

Figure 2 Suggested plant layout for dissolving casein for sodium

with water, and finely milled in a colloid mill (C). The curd–water sl

transferred to the first of two jacketed dissolving vats (F1), each

subsequently pumped from the second dissolving vat (F2) and extr

of a tubular heat exchanger (H) and then pumped via a balance tank t

may be monitored and reduced, if necessary, by addition of hot wa

edible casein products. I. Manufacture and properties. NewZealandJ

water-soluble and are typically prepared as asolution of about 20% solids prior to spray drying.Roller-dried caseinates may be prepared from moreconcentrated solutions. It is also possible to preparegranular, partly soluble, or semidispersible forms ofcaseinate in which the casein and alkali have onlypartly reacted. Sodium caseinate is the most commonform of this class of product and is prepared bymixing a solution of sodium hydroxide, bicarbonate,or carbonate with acid casein curd or dry acid caseinthat has been suspended in water and then drying theresultant solution (Figure 2). The dried powderdissolves completely in water to produce a viscous,sticky, straw-colored solution.

Calcium caseinate, on the other hand, producesa thin, opaque, white colloidal dispersion in water,similar in appearance to milk. Other caseinates,such as those of potassium and ammonium, are simi-lar in general properties to sodium caseinate. Magne-sium caseinate has properties that are intermediatebetween those of sodium and calcium caseinates.However, relatively insignificant commercial quan-tities of these products are manufactured at thepresent time.

F2

pH recordingand control

Heatexchanger

Balancetank

Viscometer andviscosity control

ater

H

hydroxide solutionsupply tank

caseinate manufacture. Dewatered casein curd is minced, mixed

urry is then mixed (D) with dilute sodium hydroxide solution and

equipped with an agitator. The sodium caseinate solution is

a alkali is added, if necessary. The solution is heated by means

o the spray (or roller) drier for drying. The viscosity of the solution

ter. From Southward CR (1985) Manufacture and applications of

ournal of Dairy Science andTechnology 20: 79–101, with permission.

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Uses in the Food IndustryC R Southward, Fonterra Research Centre,Palmerston North, New Zealand

Copyright 2003, Elsevier Science Ltd. All Rights Reserved.

Introduction

0001Although casein, as it exists in milk, has been con-sumed as ‘food’ for thousands of years, the extractedform of casein had very little application in foodsprior to 1960. Instead, from early in the 20th century,

948 CASEIN AND CASEINATES/Uses in the Food Industry

The typical composition of sodium caseinate isshown in Table 1. Acid (low-calcium) coprecipitatescan be dissolved in alkali in a similar manner to thatused for acid casein. Both rennet casein and high-calcium coprecipitate (precipitated at a pH of 6 orgreater) are usually rendered soluble by means of com-plex phosphates, such as sodium tripolyphosphate, toproduce translucent solutions with a viscosity some-what higher than that of the corresponding caseinates.

In the great majority of applications, in both edibleand technical (nonfood) uses, casein must first bemade soluble before it can be used in its final applica-tion. Although some users convert the dry casein tocaseinate themselves, others tend to purchase the case-inate directly from the producer (often as a ‘fresh-curd’ caseinate). For applications in foods. (See Caseinand Caseinates: Uses in the Food Industry.)

See also: Casein and Caseinates: Uses in the FoodIndustry; Cheeses: Starter Cultures Employed in Cheese-making; Chemistry of Gel Formation; Drying: Fluidized-bed Drying; Lactic Acid Bacteria; Pasteurization:Principles; Starter Cultures; Whey and Whey Powders:Production and Uses; Protein Concentrates and Fractions;

Fermentation of Whey

and in some cases before then, it was used as anadhesive in wood glues and paper coating, and inpaints, fibers, plastics, and leather finishing. Theintroduction of coffee whiteners and whipped top-pings, in particular, by the food industry in the USAduring the 1960s played a significant part in theestablishment of casein products in foods. Thesetwo product groups were based on vegetable fat andcontained casein in a water-soluble form (usuallysodium caseinate), together with carbohydrate, emul-sifiers, and stabilizers. They were promoted as ‘non-dairy’ foods. (As casein was derived from milk, it wasnot considered to be a dairy product. Furthermore, ithad been classified as a chemical because of its long-established use in nonfood technical applications inadhesives, paints, etc., as described above.) Nondairycoffee whiteners and whipped toppings were thuspresented as alternatives to the traditional dairyproducts of milk, cream, and whipping cream. Theyoffered advantages of lower price (because the(imported) raw materials from which they weremade were cheaper than the domestic milk solidsthey were replacing), convenience, and shelf stability(several of the products were sold in powder form).Other nondairy products followed, many of themcontaining casein, e.g., so-called imitation milks,imitation cheese, and salad dressings. Food supple-ments and dietary products were also produced anda number of these were based on casein. Thisarticle reviews the use and function of casein productsin food.

Further Reading

Australian Society of Dairy Technology (1972) CaseinManual. Parkville, Melbourne: Australian Society ofDairy Technology.

Farrell HM Jr (1988) Physical equilibria: proteins. In: WongNP, Jenness R, Keeney M and Marth EH (eds) Funda-mentals of Dairy Chemistry, 3rd edn, pp. 461–510. NewYork: Van Nostrand Reinhold.

Muller LL (1971) Manufacture and uses of casein andcoprecipitates: a review. Dairy Science Abstracts 33:659–674.

Muller LL (1982) Manufacture of casein, caseinates andcoprecipitates. In: Fox PF (ed) Developments in DairyChemistry, vol. 1. Proteins, pp. 315–337. London:Applied Science.

Mulvihill DM (1989) Caseins and caseinates: manufacture.In: Fox PF (ed) Developments in Dairy Chemistry, vol. 4,Functional Milk Proteins, pp. 97–130. London: ElsevierApplied Science.

Mulvihill DM (1992) Production, functional propertiesand utilization of milk protein products. In: Fox PF(ed) Advanced Dairy Chemistry, vol. 1, Proteins,pp. 369–404. London: Elsevier Applied Science.

Southward CR (1985) Manufacture and applications ofedible casein products. I. Manufacture and properties.New Zealand Journal of Dairy Science and Technology20: 79–101.

Southward CR (1994) Utilization of milk components:casein. In: Robinson RK (ed) Modern Dairy Technology,2nd edn, vol. 1, Advances in Milk Processing, pp.375–432. London: Chapman and Hall.

Southward CR and Walker NJ (1980) The manufacture andindustrial use of casein. New Zealand Journal of DairyScience and Technology 15: 201–217.

Spellacy JR (1953) Casein, Dried and Condensed Whey.San Francisco, California: Lithotype Process.

Whitney RMcL (1988) Proteins of milk. In: Wong NP,Jenness R, Keeney M and Marth EH (eds) Fundamentalsof Dairy Chemistry, 3rd edn, pp. 81–169. New York:Van Nostrand Reinhold.