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 syneresedcurd 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 isoelectricph 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,whichare 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. Diafiltrationwith 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 caseinomacropeptidesplit 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 NaClcontent. 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, utltrafiltrationis 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 Ca 2+ activity during heating. Adding Ca salts after heating requires a higher concentration of Ca 2+ to insolublilizethe 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-lactoglobulinand 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, CaCl 2 is added besides acid. The precipitate obtained is washed and dried, for example in a drum drier lactalbumin. It contains hardly any proteosepeptone, caseinomacropeptide, or NPN. The high lactose content and the slowness of drying are responsible for extensive Maillardreactions. Lactalbumin is insoluble in water.
Properties Rennet casein, lactalbumin, and coprecipitateare 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