Casein amino acid content

The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

The non-meat protein product must have biological quality of protein (including amino acids added) of not less than P.E.R. 2.0 (80% of casein) or an essential amino acid content (excluding tryptophan) of no less than 28% of total protein. 

Table IV). Huff et al (11) extended these observations to include enzymatic hydrolysates of the native proteins and amino acid mixtures equivalent to soy or casein. In this experiment amino acid contents were identical among the diets fed as the three forms of each protein but the structure was different (Table V). 

It should also be said again that casein, the complete protein (in terms of its amino acid content), was obtained from milk. Whether highly purified by the Merck Co. or not (as in "protene"), we have noted Hopkins i ns i stence that only hot alcohol could extract the growth substances completely. Casein, Hopkins believed, could also adsorb trace amounts of these substances. McCollum, Drummond and Osborne and Mendel would all demonstrate that lactose, also obtained from cow s milk, adsorbed variable quantities of growth promoting materials. (Anyone who has left a... 

Bitter peptides have been identified in hydrolyzates of casein (12,13), cheese (13a,b), and soy bean (14,15,15a). The bitter taste has been related to the hydrophobic amino acid content (16-20) and to chain length. Ney and Retzlaff (21) established a formula relating the bitterness of peptides to their amino acid composition and chain length. Too large a proportion of hydro-phobic amino acids gives rise to bitterness yet above a certain molecular weight, bitterness is not perceptible even when there are hydrophobic amino acids (21). Peptides that were responsible for bitterness in Cheddar cheese were rich in Pro, which occurred predominantly in the penultimate position (21a). 

We have also shown that small differences in the conditions of alkaline treatment can produce fairly large differences in the extent of racemization in casein. Temperature, of course, and length of treatment are critical. However protein concentration does not appear to influence significantly the extent of racemization (Table V). Therefore, treatment conditions may generate comparable contents of IAL but varying D-amino acid contents. 

Several other polyamides are derived from natural poly(amino acids) that are subject to a subsequent synthetic treatment. Examples are casein, groundnut protein fiber, and zein, which after a treatment with formaldehyde led to new materials with better mechanical/solubility properties. For example, casein is a mixture of several proteins that forms 3% of milk (as casein calcium salt). Casein can be fractionated into simpler proteins designated as a, 3, y, and k [37]. The amino acid content of casein is similar to... 

The physico-chemical properties of rice proteins are similar to those of casein. The main amino acid content of rice proteins is similar to that of casein and soy proteins. The rice proteins have favorable characteristics for wall material in microencapsulation. 

Comparison of the Estimated Daily Amino Acid Intake cf a tB-Year-OM Boy on a Mixed Diet and the Amino Acid Content of an Equivalent Amount of Casein... 

Casein is the other, larger, protein fraction of milk, accounting for approximately 80% of the milk proteins. Casein is the protein source of cheese and forms curds during processing because it exists as a micelle in milk. The clotting properties of casein cause it to be digested and released into the intestine slowly. -" This slow release into the intestine and ultimately circulation leads to a muted peak in plasma amino acid content compared to whey and soy proteins, which will be explained in Section 8.3. In supplemental form, casein is often made into caseinates because the native casein does not dissolve well in solution and forms clumps or curds. It is most often combined with calcium for dietary supplements, resulting in calcium caseinates. Casein is made up of three protein fractions a-casein, P-casein, and K-casein. 

Demineralised whey is used to correct the casein whey ratio in several modified (whey-based) milks containing 1 5 to 1 8 % protein examples are listed in Table 1. These milks more closely mimic the amino acid content of human milk, since the proportion of cystine is increased while those of methionine, phenylalanine and tyrosine are lowered. Whey-based modified milks appear to promote better growth in low birth weight infants, though the exact mechanism for this effect is still uncertain at present . In the absence of human milk the whey-based modified milks such as Gold Cap SMA (Wyeths), Osterfeed (Farley), Premium (Cow Gate) and Nan (Nestles) are recommended for the prevention and treatment of neonatal amino acid disorders and in my opinion are preferable to diluted cows milk or casein-based formulae for normal neonates. 

Soybean Protein Isolates. Soybean protein isolates, having a protein content of >90 wt%, are the only vegetable proteins that are widely used in imitation dairy products (1). Most isolates are derived from isoelectric precipitation, so that the soybean protein isolates have properties that are similar to those of casein. They are insoluble at thek isoelectric point, have a relatively high proportion of hydrophobic amino acid residues, and are calcium-sensitive. They differ from casein in that they are heat-denaturable and thus heat-labile. The proteins have relatively good nutritional properties and have been increasingly used as a principal source of protein. A main deterrent to use has been the beany flavor associated with the product. Use is expected to increase in part because of lower cost as compared to caseinates. There has been much research to develop improved soybean protein isolates. 

The proteins in food supplements are often hydrolyzed to short peptides to make them easier to absorb. A high content of amino acids is deleterious, however. Thus, there is ongoing interest in determining the size distribution of peptides in protein hydrolyzates. Silvestre et al. (29,30) used a PolyHEA column to compare casein hydrolyzates prepared through various methods. They were able to assess the content of the smallest peptides, as well as amino acids (Fig. 8.13). 

Walter et al. (38) measured the protein efficiency ratio (PER) of flour prepared from sweet potatoes which were cooked in a drying oven. Because the PER is determined on the basis of a diet containing 10% protein, the Jewel and Centennial sweet potatoes used in this study were stored until sufficient starch had metabolized to increase crude protein content to 11.25% (dry basis). When the flour was fed to Sprague-Dawley strain rats, the corrected PER values were 2.22 and 2.00 for Centennial and Jewel cultivars, respectively, compared to 2.50 for casein. Centennial had the highest PER value of the two cultivars because its NPN content was lower. The net effect of increased NPN content is to lower the amount of essential amino acids as a percentage of the total nitrogen and thus decrease the PER value. 

Friedman (21) studied the effect of pH on the amino acid composition of wheat gluten. At pH 10.6 and above (65 C, 3 hours) no cystine was present. LAL increased with pH above 10.6. Lysine decreased over the same range of pH s, while serine and threonine contents dropped sharply at pH 13.9. Friedman concluded that cystine is most sensitive to alkali and that LAL will form most readily if lysine residues are in proximity to the dehydroalanine formed from cystine. Thus, he explained that different steric considerations may explain the different susceptibilities of wheat gluten, casein, and lactalbumin to LAL formation. 

Casein is low in sulphur (0.8%) while the whey proteins are relatively rich (1.7%). Differences in sulphur content become more apparent if one considers the levels of individual sulphur-containing amino acids. The sulphur of casein is present mainly in methionine, with low concentrations of cysteine and cystine in fact the principal caseins contain only methionine. The whey proteins contain significant amounts of both cysteine and cystine in addition to methionine and these amino acids are responsible, in part, for many of the changes which occur in milk on heating, e.g. cooked flavour, increased rennet coagulation time (due to interaction between /Mactoglobulin and K-casein) and improved heat stability of milk pre-heated prior to sterilization. 

All the caseins have a high content (35-45%) of apolar amino acids (Val, Leu, lie, Phe, Tyr, Pro) and would be expected to be poorly soluble in aqueous systems, but the high content of phosphate groups, low level of... 

The caseins adsorb readily at air-water and oil-water interfaces due to their open structure, relatively high content of apolar amino acid residues and the uneven distribution of amino acids. This gives the caseins very good emulsifying and foaming properties, which are widely exploited in the food industry. 

The most obvious fluorescent compound in milk is riboflavin, which absorbs strongly at 440-500 nm and emits fluorescent radiation with a maximum at 530 nm. Riboflavin in whey is measured easily by fluorescence (Amer. Assoc. Vitamin Chemists 1951). Proteins also fluoresce because of their content of aromatic amino acids. Part of the ultraviolet radiation absorbed at 280 nm is emitted at longer wavelengths as fluorescent radiation. A prominent maximum near 340 nm is attributable to tryptophan residues in the protein. Use of fluorescence for quantitation of milk proteins was proposed by Konev and Kozunin (1961), and the technique has been modified and evaluated by several groups (Bakalor 1965 Fox et al. 1963 Koops and Wijnand 1961 Porter 1965). It seems to be somewhat less accurate than desired because of difficulties in disaggregating the caseinate particles and in standardizing instruments. It also involves a basic uncertainty due to natural variations in the proportions of individual proteins which differ in tryptophan content. 

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