Casein solutions, mixtures with

When the mixture stands over night in a filter jar the milk fat collects at the surface and can be separated cleanly at the pump. The filtrate is combined with the rest of the casein solution and the substance is again precipitated by the addition of 10-20 c.c. of glacial acetic acid. Finally the precipitate is collected by filtration... 

Vitamin-Free, Acid-Hydrolyzed Casein Solution Prepare the solution by mixing 400 g of vitamin-free casein with 2 L of boiling 5 N hydrochloric acid. Autoclave for 10 h at 121°. Concentrate the mixture by distillation under reduced pressure until a thick paste remains. Redissolve the paste in water, adjust the solution to pH 3.5 0.1 with a 10% solution of sodium hydroxide, and dilute with water to a final volume of 4 L. Add 80 g of activated charcoal, stir for 1 h, and filter. Repeat the treatment with activated charcoal. Filter the solution if a precipitate forms on storage. 

In addition, they are used in combination with casein solutions and synthetic resin emulsions. Whereas starch ethers and esters and also aldehyde starches are used to only a limited extent in the adhesives field, the thermal degradation products of starches, the water-soluble dextrins, are still important in quantitative terms as raw materials for adhesives. They are used on their own in aqueous form or as mixtures with synthetic resin emulsions. 

Contrary to the case of P-casein/Tween 20 systans, although the surface pressure isotherms shed some light on the surface structure of whole casein/Tween 20 systems, the information extracted does not provide a full explanation to the behavior of foams stabilized by this system. Taking into account the key information provided by the confinement in thin liquid films as regards the foam stability of whole casein and P-casein solutions, which was examined in the previous section, let us evaluate the properties of the foam films stabilized with whole casein/Tween 20 mixtures. Table 10.2 shows the thickness of foam films stabilized by pure whole casein, pure Tween 20 and two mixed systems under similar conditions to the foam stability, and the surface pressure experiments. The film thickness is measured by using Scheludko s microinterferometric method (Maldonado-Valderrama and Langevin, 2008). 

Tryptophane.—In an 8-1. (2-gal.) bottle is placed 600 g. of commercial casein (coarse powder), which is then covered with about 3200 cc. of tap water at 370 (Note 1). The bottle is shaken until all of the casein is moistened. A solution of 60 g. of anhydrous sodium carbonate (Note 2) and 6 g. of sodium fluoride (Note 3) in 1 1. of water at 37° is added. A thin paste of 20 g. of commercial pancreatin in roo cc. of water (370) is poured in. The mixture is covered with a layer of toluene (80 cc.), diluted to 6 1., stoppered, shaken thoroughly, and placed in a warm room or bath at 370. 

Whole milk (2 litres) is diluted with an equal volume of water at 30°-40° and commercial rennet (0-1 g.), dissolved in a few cubic centimetres of water, is added. The mixture is then left at the same temperature until separation of the casein is complete (about two hours). The whey is filtered through a filter cloth, and after the liquid has run off the residue is pressed down well. The casein, which contains a great deal of fat, is ground in a mortar with a little 1 per cent sodium hydroxide solution 1 to 1-5 litres of sodium hydroxide solution of the same concentration are then poured on to the resulting paste, and the mixture is gently warmed in a porcelain basin until all but the fat dissolves. 

At all temperatures, asl-CN B and C are insoluble in calcium-containing solutions and form a coarse precipitate at Ca2+ concentrations greater than about 4 mM. asl-CN A, from which the very hydrophobic sequence, residues 13-26, is deleted, is soluble at [Ca2+] up to 0.4 M in the temperature range 1-33°C. Above 33°C, it precipitates but redissolves on cooling to 28°C. The presence of asl-CN A modifies the behaviour of asl-CN B so that an equimolar mixture of the two is soluble in 0.4 M Ca2+ at 1°C asl-CN B precipitates from the mixture at 18°C and both asl-CN A and B precipitate at 33°C. aBl-CN A does not form normal micelles with K-casein. Since asl-CN A occurs at very low frequency, these abnormalities are of little consequence in dairy processing but may become important if the frequency of asl-CN A increases as a result of breeding practices. 

P-Casein (13 mg) containing 0.036 fid M-P-C was subjected to plasmin hydrolysis for 45 min and the reaction mixture was dissolved in 7 mL column buffer (5mM Tris—3mM NaCl—urea, pH 8.55) together with 100 mg whole casein that had been alkylated with iodoacetamide. The sample solution was applied to a column (1.6 X 50 cm) of DEAE-cellulose equilibrated with column buffer. Elution was with a NaCl gradient (3.0-155mM) in column buffer (gradient volume, 1.0 L) 5.0 mL fractions were collected. Under the conditions used as as-caseins remained adsorbed to the column K-caseins were eluted in Fractions 35-56 Am measurement (----------) radioactivity (--) (28). 

The direct determination of some major elements (Ca, K, Mg, Na, and P) and Zn by ICP-AES was performed in powdered milk [14]. Samples were diluted with a 5 or 10 percent (v/v) water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. No decrease in analyte emission intensities was observed. Reference solutions were prepared in 10 percent (v/v) mixed amine solution, and no internal reference element was needed for ICP-AES. The direct technique is as fast as slurry approaches, without particle size effects or sensitivity losses. 

In the preparation of i -tryptophane from 600 g. of casein suspended in 3.2 1. of water at 37° by digestion with commercial pancreatin (two 20-g. batches), a solution of 60 g. of NajCOa and 6 g. of NaF in 100 ml. of water is poured in prior to addition of the enzyme as a thin paste in water. The mixture is covered with a layer of toluene, diluted to 6 I., shaken thoroughly, and let stand at 37° for 5 days a second butch of enzyme is added and the mixture let incubate for 12 days more. The sodium fluoride probably inhibits (he action of the oxidases. Workup affords 4.0-4.1 g. of pure I.-tryptophane and 17.0-18.2 g. of pure i.-tyrosine i.-tyrosine... 

Figure 1 Relationships of S with interfacial tension and emulsifying activity of proteins. I, bovine serum albumin 2, /3-lactoglobulin 3. trypsin 4, ovalbumin 5, conalbuntin 6, lysozyme 7, K-casein 8, 9, I0, II, and 12, denatured ovalbumin by heating at 85°C for l, 2, 3, 4, and 5 min respectively 13, 14, 15, 16. 17, and 18. denatured lysozyme by heating at 85"C for l, 2, 3, 4, 5, and 6 min respectively 19, 20, 21, 22, and 23, ovalbumin bound with 0.2, 0.3, 1.7, 5.7, and 7.9 mol of sodium dodecyl sulfate/mol of protein respectively 24, 25, 26, 27, and 28, ovalbumin bound with 0.3, 0.9, 3.1,4.8, and 8.2 mol of linoleate/mol of protein respectively. Interfacial tension measured at corn oil/0.20c protein interface with a Fisher Surface Tensiontat Model 21. Emulsifying activity index calculated from the absorbance at 500 nm of the supernatant after centrifuging blended mixtures of 2 ml of corn oil and 6 ml of 0.5% protein in 0.01 M phosphate buffer, pH 7.4 S initial slope of fluorescence intensity (FI) vs. percent protein plot. 10 /al of 3.6 mM m-parinaric acid solution was added to 2 ml of 0.002 to 0.1% protein in 0.01 M phosphate buffer, pH 7.4, containing 0.002% SDS. FI was measured at 420 nm by exciting at 325 nm. (From Ref. 2. Reprinted by permission.)...

Proteolytic activity was assayed as described by Kembhavi et al. [9], with modification. The reaction mixture was made up of 0.4 mL of casein (Sigma) 0.5% (w/v) in distilled water and 0.4 mL 0.2 M acetate buffer, pH 5.0, to whieh 0.2 mL of the crude enzyme solution was added. The reaction was carried out at 60°C and stopped after 30 min with 1 mL of 10% trichloroacetic acid (TCA). Test tubes were centrifuged at 5,000 rpm/5 min, and the absorbance of the supernatant was measured at 280 nm. An appropriate control was prepared in which the TCA was added before the enzymatic solution. One unit of enzyme activity (U) was arbitrarily defined as the amount of enzyme required to cause an increase of 0.01 in absorbance at 280 nm under the assay conditions. 

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