Milk Protein Products:

Casein & Whey

Introduction

Currently, various types of casein and of whey protein

are widely used in food processing, due to:

� Provide foods with a specific nutritive value

Infant formula, the application of partially

hydrolyzed protein for people who have allergic

problem, boosting protein content in beverages &

biscuits

� Replace more expensive proteins

Protein-rich whey products can (partially) replace

skim milk in ices, desserts, beverages, etc

Introduction

� Provide a product with specific physical properties

The preparation of stable emulsions (salad dressings,

desserts)

Foam products (toppings, meringues)

� Make novel products

An increasing trend in the food industry is the

production of ‘manufactured foods’ from fairly pure

and durable components. Examples are cheese-like

sandwich spreads, coffee creamers, and meat

analogues.

Manufacture

The properties of the milk protein preparations may greatly depend on the pretreatment of the milk or the whey.

Heat treatment is required to kill bacteria & to inactivate enzymes.

Heating can cause denaturation � decreased solubility of serum proteins.

This content depends also on the extent to which fat globules have become covered with plasma proteins � hardly be removed from the protein preparation by the common purification methods.

Bacterial spoilage and plasmin activity can cause proteolysis.

Casein Manufacture

Casein preparations are made from sharply skimmed milk.

The heat treatment of the (skim) milk is such that very little serum protein becomes denatured.

Denatured protein ends up in the casein product.

Casein is most often accumulated by rendering it insoluble.

Various types of casein preparations: rennet casein, acid casein, caseinate, micellar casein.

Casein Manufacture

Rennet Casein

� The casein is rendered insoluble by addition of calf rennet,

followed by stirring at a temperature increasing to about

55°C.

� The fine syneresed curd particles so formed are separated

by centrifugation, washed with water, pressed to remove

moisture, and then dried, for instance, in a drum or a belt

drier.

� The resulting product is composed of calcium

paracaseinate–calcium phosphate, with some impurities.

� It is insoluble in water and has a high ‘ash’ content.

Casein Manufacture

Acid Casein

� Skim milk is acidified, while stirred, with hydrochloric acid

(mostly), lactic acid, or sulfuric acid, until the isoelectric pH

of casein (4.6) is reached.

� The casein then is insoluble.

� The temperature applied is quite critical. At a high

temperature large lumps are formed,which are difficult to

dry; a low temperature causes a fine voluminous

precipitate, which is hard to separate. The optimum

temperature is about 50°C.

� The process is continued as described for rennet casein.

Casein Manufacture

Caseinates

� Acid-precipitated casein can be dissolved in alkali (NaOH,

KOH, NH4OH, Ca(OH)2, and Mg(OH)2), and the resulting

solution can be spray-dried � Na-caseinate (the most

common product), K-caseinate, Ca-caseinate

� These products can be well soluble in water and be almost

flavorless — if the pH during manufacture was never

higher than 7.

� A combination of a high pH and a high temperature will

result in formation of some lysinoalanine, which is

considered undesirable.

Casein Manufacture

Micellar Casein

� This can be obtained from skim milk by microfiltration; the

product is generally called phosphocaseinate.

� When using a membrane of pore size 0.1 µm, by far most

of the casein is retained, whereas virtually all serum

proteins can pass the membrane.

� Diafiltration with water is used to further remove

dissolved substances.

� The micelles obtained appear to have properties close to

those of natural casein micelles, also after drying and

dispersion in skim milk ultrafiltrate.

Whey Protein

Whey may vary substantially in composition.

• Whey obtained in classical cheese making.

� It contains soluble components of milk, the

caseinomacropeptide split off κ-casein; active rennet

enzymes; starter bacteria; lactic acid; and some globular

fat, which generally is largely removed beforehand by

centrifugal separation.

� The acidity of the whey greatly varies with the type of

cheese made.

� The whey may have been diluted with water and/or

contain some added nitrate.

Whey Protein

• Whey with a high NaCl content.

� It is resulted from Cheddar-type cheese making or from the manufacture of rennet casein.

� This whey is low in fat content and contains no starter bacteria, nor lactic acid.

• Whey resulting from the manufacture of acid casein.

� The fat content is low and it contains no rennet or casein macropeptide.

� The pH is about 4.6, and it contains increased amounts of calcium and phosphate .

In all cases, about half of the protein in whey consists of β-lactoglobulin.

Types of Whey Protein Preparations

Whey Protein Concentrate (WPC).

� The name is generally used for preparations containing 35 to 80% ‘total protein.’

� The preparations with a low protein content are often called skim milk replacers.

� WPC is made of delactosed, desalted whey, which is concentrated about 10 x by evaporation, to obtain lactose crystals.

� The mother liquid then is desalted.

� Drying of the remaining liquid results in WPC.

� A considerable proportion of the nitrogen is NPN, generally more than 20%.

� To obtain a higher protein concentration and a purer

product, utltrafiltration is generally used.

� To make purer products, diafiltration can be applied.

� The liquid is commonly spray-dried and the resulting WPC

powders can be highly soluble.

� The part of the protein that does not dissolve because it is

heat-denatured greatly depends on the pH and the Ca2+

activity during heating.

� Adding Ca salts after heating requires a higher

concentration of Ca2+ to insolublilize the protein.

Whey Protein Isolate (WPI).

� The name is generally reserved for preparations in

which 90% (or more) of the dry matter consists of

whey protein.

� Preferably, the whey used for its manufacture is

relatively pure; it is even better to use a

microfiltration permeate of skim milk.

� WPI can be produced, like WPC, by ultrafiltration; at

least one diafiltration step then is necessary.

� Other methods such as ion exchange also could be used.

� The whey is acidified to pH 3.2, where the proteins

present are predominantly positively charged � sieving �

washing in alkali (pH 8) � desorption of protein � drying.

� The protein is for almost 80% β-lactoglobulin and some

15% α-lactalbumin; it contains little of the other serum

proteins. This composition markedly enhances gel forming

properties.

� Besides, the protein is almost fully devoid of lipids, which

is of advantage when using it for foam formation.

Lactalbumin

� Heating sour cheese whey to precipitate its protein and to recover it � precipitate is impure.

� It is pressed, usually salted, and sometimes matured.

� A similar process can be applied to yield denatured whey protein. Often, CaCl2 is added besides acid.

� The precipitate obtained is washed and dried, for example in a drum drier � ‘lactalbumin’.

� It contains hardly any proteose peptone, caseinomacropeptide, or NPN.

� The high lactose content and the slowness of drying are responsible for extensive Maillard reactions.

� ‘Lactalbumin’ is insoluble in water.

Properties

Rennet casein, ‘lactalbumin,’ and coprecipitate are preparations that are fully insoluble in water.

They are applied in solid-like products such as biscuits. They can also be used to make ‘texturized’ products in an extruder, or for dry spinning.

In almost all other products the protein to be used must dissolve.

Increasing viscosity � caseinates

Gelling agent � caseinates, whey protein

Emulsifier � caseinates, micelar casein

Foaming agent