Protein, separation skim milk

In 1877 O. Hammarsten distinguished three proteins in milk casein, lactalbumin and lac-toglobulin. He also outlined a procedure for their separation skim milk is diluted then acidified with acetic acid. Casein flocculates, while the... 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Ultrafiltration. Membranes are used that are capable of selectively passing large molecules (>500 daltons). Pressures of 0.1—1.4 MPa (<200 psi) are exerted over the solution to overcome the osmotic pressure, while providing an adequate dow through the membrane for use. Ultrafiltration (qv) has been particulady successhil for the separation of whey from cheese. It separates protein from lactose and mineral salts, protein being the concentrate. Ultrafiltration is also used to obtain a protein-rich concentrate of skimmed milk from which cheese is made. The whey protein obtained by ultrafiltration is 50—80% protein which can be spray dried. 

Calcium caseinate is produced from skim milk by adding an acid to cause the protein to coagulate, at which point it can be filtered to separate the curds from the whey. 

Skim milk prepared by mechanical separation (see Chapter 3) is used as the starting material for the preparation of casein and whey proteins. 

In the fractionation of the milk proteins, usually the first step in the process is to separate the so-called whole casein from the whey in a skim milk. A number of procedures are available (McKenzie 1971C), but the most commonly used method is based upon classical acid precipitation at the pH of minimum solubility. Several different temperatures have been employed 2, 20, and 30°C. Except for precipitation at 2°C, where minimum solubility occurs at pH 4.3, the skim milk is adjusted to pH 4.5-4.6 with hydrochloric acid (1 M). A more recent investigation of the relationship of temperature and pH to the completeness of casein precipitation indicated that optimum yield was obtained at pH 4.3 and 35°C (Helesicova and Podrazky 1980). 

Protein Composition of Milk. Skim milk is a colloidal suspension of extreme complexity. The particulate phase, the casein micelles, consists primarily of a mixture of asi, as2, / , and x-caseins combined with calcium ions and an amorphous calcium-phosphate-citrate complex. The soluble phase contains lactose, a fraction of the caseins and calcium, and, in raw milk, the whey proteins, which are predominantly /3-lacto-globulin and a-lactalbumin. When milk is centrifuged at high speed (in our experiments, 30 min at 110,000 X gravity), the casein micelles sediment. This permits one to separate the two physical phases of skim milk and to measure changes in composition of the phases resulting from... 

Along this line of thought, Michalke and Schramel [75] studied pooled human milk samples from days 7-14 after delivery. They developed a method for the preparative separation of the proteins from skimmed human milk, which was proven to preserve the metal protein complexes as well as keeping the samples and fractions free from Cd contamination. For this purpose an SEC separation was applied and fractions were collected for Cd determination by voltammetry... 

As can be seen from Figure 19.27 skim milk can be fractionated by means of UTP MF (0.1 pm), in combination with an UF diafiltration step, in its two main protein fractions, i.e. native casein micelles and native whey proteins since no heat treatment step was required to separate the proteins. The MF permeate can be considered a sort of sweet whey, however, without containing the caseinomacropeptide (CMP). This MF permeate can be further concentrated to obtain a WPC product. The... 

Milk of UF-standardized protein and total solids content enables the production of fermented dairy products of improved quality and characteristics compared with those produced from milk fortified with milk powder or evaporated milk [11]. Due to the similarity of the protein fractions in HMPP and those of skim milk and the virtual absence of lactose, Mistry and Hassan [134] suggested its utilization for the development of new dairy products and the improvement of existing ones. When these authors used HMPP to produce nonfat yogurt, they found that fortification level up to 5.6% protein can produce acceptable yogurt with smooth texture and firm body that did not exhibit whey separation even without the addition of stabilizers. They noted, however, that >5.6% protein concentration, the yogurt becomes excessively firm and has a grainy texture and flat flavor. 

In the manufacture of fresh cheeses, e. g. quark, the pasteurised skim milk is inoculated with micro-organisms (Sc. lactis, Sc. cremoris). To accelerate the thickening, the enzym chymosin is added. After ripening - with a pH value of about 4.6 - the coagulated milk must be pumped through a separator, possibly including an ultrafiltration system, in order to separate the sour whey. The ultrafiltration would separate the whey into 2 phases the permeate (water soluble) and the retentate (protein phase). Finally the quark, retentate, cream, (fruit) preparations, flavourings or spices and herbs are added. 

The yeast produced by continuous culture techniques is separated from the liquid medium and solvent washed by centrifugation or filtration techniques. After drying, a protein supplement is obtained, which contains 65-68% protein and is suitable for addition to animal feeds. This protein content compares very favorably with that of dry fish meal, which contains about 65%, and dry skim milk powder with about 32%. The SCP processes have operated on the thousands of tonne/year scale in the U.K., France, and Italy, but regulatory problems with facilities operating on unpurified gas oil feedstocks have caused some shutdowns [64]. Nevertheless, because of a cell mass doubling time of 2.5-3 hr and the efficient carbon conversion to protein of this technology, these developments deserve to be explored further. 

Figure 15.14 Separation of milk proteins [reproduced with permission from B.B. Gupta, J. Chromatogr., 282, 463 (1983)]. Conditions sample, 100 pi of whey from raw skimmed milk (casein precipitated at pH 4.6) column, 60 cm x 7.5 mm i.d. stationary phase, TSK 3000 SW (silica, 10pm) mobile phase, 0.5 ml min buffer containing 0.1 M NaH2PO4, 0.05 M NaCl and 0.02% NaNa (pH 6.8) UV detector, 280 nm. Peaks (with molecular masses) 1 = high molecular weight proteins 2 = -y-globulin (150000) 3 — bovine serum albumin (69000) 4 = /3-lactoglobulin (35000) 5 = a-lactalbumin (16500) other components not identified.

The presence of both acidic and basic side chains has led to protein such as casein acting as amphoteric electrolytes and their physical behavior will depend on the pH of the environment in which the molecules exist. The isoelectric point for casein is about pH = 4.6 and at this point colloidal stability is at a minimum. This fact is utilized in the acid coagulatimi techniques for separating casein from skimmed milk. 

Brodbeck and Ebner found that the soluble lactose synthetase from milk can be separated into two protein components, A and B, which individually do not exhibit any catalytic activity however, their recombination restores full lactose synthetase activity. The B fraction has been crystallized from bovine skim milk and bovine mammary tissue, and was identified as a-lactalbumin. It was thus found that a-lactalbumin can be substituted for the B protein of lactose synthetase. Lactose synthetases from the milk of sheep, goats, pigs, and humans were also resolved into A and B proteins, and the fractions from these species were shown to be qualitatively interchangeable in the rate assay of lactose synthesis. Determination of the amino acid sequence of a-lactalbumin (B fraction) has shown a distinct homology in the sequence of amino acids of a-lactalbumin and hen s egg-white lysozyme, suggesting that lysozyme and a-lactalbumin have evolved from a common ancestral gene. 

SDS-PAGE gel is good for separating Ras proteins. If Flag-Ras proteins will be monitored, use more than 3% skim milk in TEST for first and second antibody to reduce background. For anti-Ras antibody (clone RaslO), 3% BSA or 3% goat serum in TEST works well. 

CAS 92129-90-3 Synonyms Lacto-serum Definition Liq. substance obtained by separating coagulum from milk, cream, or skim milk in cheesemaking as sweet or acid whey, cone, whey, or dried whey contains typically 5% lactose, 1% protein, 1% fats, salts, lactic acid Uses Food ingred. in cheese-making animal feed ingred. 

The first industrial application of SEC for protein solutions were for desalting dairy products (66). Large columns (2500 liters) were used to separate proteins in whey or skim milk from low-molecular-weight sugars and salts. SEC is also used in the deethanolization of human serum albumin (HSA) (67) produced by the Cohn cold ethanol procedure. The purification of insulin was the first successful industrial application of SEC for protein fractionation (68), followed by the fractionation of HSA proteins (69). 

Dairy products, such as mUk powder, should be prepared exclusively from milk and should not contain solids from whey. The absence of rennet whey solids from mUk powder is required according to legislation. Considering the lower price of rennet whey, it can be an attractive adulterant of milk powder. Thus, the presence of CMP can be a good marker to evaluate milk powder authenticity. Whey powders contain about 12% protein and 75% lactose. Caseinomacropeptide can account for more than 16% of the protein content. RP-HPLC can be used to detect rennet whey in mUk powder by CMP measurement. For this purpose, powdered milks were reconstituted with deionized water. Skim milks were prepared by separating the fat from the whole milk by centrifugation at 700 X g (at 4°C) for 10 min. Caseinomacropeptide and... 

The native phosphocaseinate suspension (NPCS) was prepared from skim milks of cow, ewe, and goat by microfiltration and diafiltration. Whey protein concentrate (WPG) was separated from previous cow milk microfiltrate. Combined cow casein powders (CCP) were obtained by two techniques (i) WPC and Polydextrose Litesse (PDL) from Pfizer Co. (Orsay, France) were first mixed into cow NPCS retentate before freeze-drying to obtain 4%, 8%, and 12% PDF/total solid (TS) and 4%, 8%, and 12% WPC/TS powders and (ii) mineral salts were added to cow NPCS concentrate at 50°C for 30 min before spray co-drying. In the NMT measurements, the samples include 1 g of a powder per 20 mL of water. 

Figure 3. Separation of milk proteins using a weak anion-exchanger. Column, 7.75 mm x 100 mm, 15 micron BAKERBOND WP-PEI mobile phase, initial buffer (A) 10 mM Tris, pH 7.0 final buffer (B) 2 M sodium acetate, pH 6.0 gradient, 0—100% B over 60 min flow-rate, I ml/min detection UV (280 nm), 0.5 AUFS sample, 0.05 ml (LIPOCLEAN -extracted skim milk, diluted three times with buffer A). Peaks c, conalbumin b, 6-lactoglobulin B a, p-lactoglobulin A.

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