DAIRY PRODUCTS - WHEY

Whey, the greenish-yellow liquid produced from the manufacture of cheese, contains about half of the solids of whole milk. Its composition depends largely on the variety of cheese being made. These solids are valuable additions to the functional properties of various foods, as well as a source of valuable nutrients. The techniques of concentration, drying, and reverse osmosis recover all of the whey solids. Crystallization, ion exchange, and membrane systems such as ultrafiltration and electrodialysis effect fractionating whey into concentrates of protein, minerals, and lactose. Figure 1.13 shows an outline for the manufacture of whey products and milk protein concentrate. The proximate composition of dry whey, whey products, caseinates, and milk protein concentrates is shown in Table 1.9.

Dry Sweet Whey

Dry sweet whey is produced by drying of defatted fresh whey obtained from the manufacture of Cheddar, Swiss, and other cheeses. It contains all the constituents except water in the same relative proportion as in liquid whey. Dry acid whey is similar to dry sweet whey but is produced by drying of fresh whey obtained from Cottage and Ricotta cheese manufacture. Spray drying of condensed whey converts sweet whey into a stable, nonhygroscopic, and noncaking product. In this process, high solids whey concentrate is spray dried to a free moisture content of 12–14%, causing lactose to take on a molecule of water and become crystallized. This causes whey solids to convert from a sticky, syrupy-like material into a damp powder with good flow characteristics. For drying acid cottage cheese whey, a commercial dryer combines spray drying, with through-flowcontinuous bed drying. The concentrate is spray dried in the hot air chamber to 12–15% moisture. The particles fall to a continuous, porous, stainless-steel belt where lactose undergoes rapid crystallization. Crystallization of lactose before final drying is necessary for drying acid whey. A belt conveys the product to another chamber where the whey is further dried by dehumidified air that moves through the porous bed. Dry sweet whey is widely used in bakery products, dry mixes, process cheese foods and spreads, frozen desserts, sauces, meat emulsions, confections, soups, gravies, snack foods, and beverages. Dry acid whey has an additional functional attribute of providing acid flavor in certain foods and it imparts desirable textural properties to bakery items.

Fractionated Whey Products

Membrane technology is used for partial concentration (reverse osmosis), fractionation of solutes (lactose, minerals) from macromolecules like proteins, fat globules, colloidal particles (ultrafiltration), and demineralization (ion exchange, electrodialysis) of whey, its fractions, and milk. These processes produce highly functional ingredients and are commonly used in whey concentration and fractionation. The two are pressure-activated processes that separate components on the basis of molecular size and shape. Reverse osmosis is the process in which virtually all species except water are rejected by the membrane. The osmotic pressure of the feed stream in such a system often will be quite high. Consequently, to achieve adequate water flux rates through the membrane, such systems often use hydrostatic operating pressures of 5883.6 kg/cm2 (600 psi) or greater. Ultrafiltration refers to the process in which the membrane is permeable to relatively low molecular weight solutes and solvent (permeate), but is impermeable to higher molecular weight materials (retentate). The permeability and selectivity characteristics of these membranes can be controlled during the fabrication process so that they will retain only molecules above a certain molecular weight. Thus, ultrafiltration is essentially a fractionating process, while reverse osmosis is effectively a concentrating process. One advantage of ultrafiltration over other processes is that by varying the amounts of permeate removed, a wide variety of protein concentrates, ranging up to 60% protein, can be obtained. Higher levels can be obtained by simultaneously adding freshwater and further concentrating by ultrafiltration. The permeate is used for manufacture of milk sugar, lactose, by condensing and crystallization. Lactose crystals are harvested and dried in a tumble dryer.

Reduced Lactose Whey

Reduced lactose whey is produced from whey by partial crystallizing out lactose and recovery of mother liquor by centrifugation. Lactose content of the dry product is 60% or less.

Reduced Minerals Whey

Reduced minerals whey is produced from whey by selective removal of a portion of minerals. Ash content of the dry product is 7% or less. Demineralization processes have helped in the development in an array of whey products. Excessive mineral content makes whey distasteful, and they can have an adverse effect on the physical properties of some foods. The two most widely used demineralization processes for whey are ion exchange and electrodialysis. In the ion-exchange process, whey is passed through two containers which are filled with special synthetic resins which have the ability to exchange ions. In the first container, the special synthetic resins exchange hydrogen ions for cations in the whey. Here, the positive ions of the salt are captured and acid is formed by the release of hydrogen ions. The whey is then passed over the anion exchanger where hydroxyl ions are exchanged for negative ions of the salt, and water is formed. When the mobile ions of the resins are completely replaced by other ions, the resin must be regenerated for further use. This is done by passing an acid (hydrochloric) solution through the cationic exchanger, and a basic solution (sodium chloride) through the anionic exchanger. Electrodialysis, a combination of electrolysis and dialysis, is the separation of electrolytes, under the influence of an electric potential through semipermeable membranes. The driving force is an electric field between the anode (positively charged) and the cathode (negatively charged). Between the anode and the cathode, a number of ion-selective membranes are placed which are permeable only to anions or cations. Every other membrane has a positive charge repelling positive ions and allowing negative ions to pass, and in between there is a negatively charged membrane doing just the opposite. In principle, whey is pumped through every second space between two membranes, and a solution of sodium chloride (cleaning solution) is pumped through the compartments between the whey streams. The ions move from the whey stream into the cleaning solution where they are retained, because they cannot move any further. The cleaning solution contains minerals, acid, some lactose, and small nitrogenous molecules. The membranes are cleaned chemically. Protein molecules remain in the fluid while the minerals are removed. The process results in a protein concentrate.

Lactose

Lactose is crystallized from condensed whey or from permeate (50–60%, solids) obtained by ultrafiltration fractionation of milk or whey. The supersaturated solution is cooled under specific conditions to crystallize lactose. Lactose crystals are harvested and washed to remove the mother liquor and dried. Crude lactose obtained this way contains approximately 98% lactose. Edible and USP grades are produced from crude lactose by protein precipitation, decolorization with activated carbon and subsequent demineralization. Lactose is further refined by recrystallization, followed by spray drying.

Whey Protein Concentrates and Isolates

Whey protein concentrates are products derived from whey by removal of minerals and lactose. The process of protein concentration utilizes ultrafiltration, electrodialysis, and ion-exchange technologies. On dry basis, the protein concentrate contains a minimum of 25% protein. Whey protein isolate contains at least 92% protein. Whey protein concentrate of 34% protein is commonly used as a stabilizer in yogurt, bakery mixes, dietetic foods, infant foods, and confections. Its water binding, fat-like mouth-feel, and gelation property is particularly useful in these products. Wheat protein concentrate of 50% or 80% protein offers distinct functional attributes. It is especially suited for use in nutritional drinks, soups, bakery, meat, dietary foods, and protein fortified beverages. It gives clear suspensions over a wide pH range and has a bland flavor. Some applications require undenatured ingredients to maximize water-binding capacity during food processing. It is also available in gel-forming version.

Excerpts from "Dairy Processing & Quality Assurance", Editor Ramesh C. Chandan, published 2008 by Wiley-Blackwell, U.S.A. p.27-30. Adapted and illustrated to be posted by Leopoldo Costa.

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