Casein isolate production

Products prepared from soy protein products and resembling chicken, ham, frankfurters, and bacon are available commercially. Soy protein isolates are used in place of milk proteins or sodium caseinate in products such as coffee creamers, whipped toppings, yogurt, and infant formulas (see Dairy substitutes). Soy protein products also are used in snacks and in baked foods. 

Protein-Based Substitutes. Several plant and animal-based proteins have been used in processed meat products to increase yields, reduce reformulation costs, enhance specific functional properties, and decrease fat content. Examples of these protein additives are wheat flour, wheat gluten, soy flour, soy protein concentrate, soy protein isolate, textured soy protein, cottonseed flour, oat flour, com germ meal, nonfat dry milk, caseinates, whey proteins, surimi, blood plasma, and egg proteins. Most of these protein ingredients can be included in cooked sausages with a maximum level allowed up to 3.5% of the formulation, except soy protein isolate and caseinates are restricted to 2% (44). 

A significant problem is the wide variation in properties in the same type of product both from different manufacturers and from the same source. More recendy there has been vast improvement in the consistency of these products from a given manufacturer and usage in dairy substitutes is expected to expand. These isolates do have a higher protein efficiency ratio (PER) than casein and are equal to egg protein. 

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. 

Isolated soy proteins have also been used in whipped toppings. Soy-protein-based toppings have a lower protein concentration than caseinate-based toppings. Formulations ate adjusted to protein levels, and higher protein levels can result in off-flavors. Typical formulations for a Hquid frozen, prewhipped product are given in Table 18. 

Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

Considerable interest has been shown in uses of vegetable food proteins in cheese-type products. Attempts have been made to coprecipitate casein and vegetable protein in the typical vat process for making cheeses (35). Rhee (36) has found that up to 50% peanut protein isolate and 25% soybean isolate can be effectively substituted for sodium caseinate in the preparation of imitation cheeses. 

Hermansson ( 2) examined the effect of ionic strength on swelling-of soy isolate, caseinate, and WPG products. The effect of NaCI on water absorption was not consistent among the products. Generally, as ionic strength increased from 0.0 to 1.0 M NaCI, water absorption increased for the soy isolate and caseinate. 

One of the important developments in dairy technology in recent years has been the fractionation of milk into its principal constituents, e.g. lactose, milk fat fractions and milk protein products (caseins, caseinates, whey protein concentrates, whey protein isolates, mainly for use as functional proteins but more recently as nutraceuticals , i.e. proteins for specific physiological and/or nutritional functions, e.g. lactotransferrin, immunoglobulins). 

Isolated as2-casein in solution is also very susceptible to plasmin eight peptide bonds are hydrolysed with the production of 14 peptides. Plasmin also hydrolyses as2-casein in milk but the peptides formed have not been identified, although at least some are included in the proteose-peptone fraction. 

Creamer (1974) to separate asl-casein-A from whole casein containing both the A and B variants. The B variant was degraded with pepsin or rennet, and the A variant was isolated from the degradation products on a DEAE-cellulose column with an NaCl gradient (0.0 to 0.5 M) in 4.5 M urea buffered at pH 5.5 containing 0.1% mercaptoethanol. 

Figure 1.2. Differential thermal analysis for the humic acid fraction isolated in NaOH from a sapric histosol (1), from the acid precipitate isolated from products of the reaction of meth-ylglyoxal with glycine (2), and from the acid precipitate formed from the reaction of glucose with glycine (3), alkali lignin (4), casein (5), lignin-casein 3 1 complex (6), and lignin-casein 6 1 complex (7).

Casein heated in aqueous solution with furfural rapidly turns orange-brown. Melanoidins (> 10 kDa), isolated by ultracentrifugation, were enzymically hydrolysed and the product was separated by HPLC. Two peaks led to red compounds in the ratio 1 7, which were unequivocally identified by Hofmann191 as the lysine analogues of 24a and 24b (MM = 0.476 kDa), respectively. This is the first demonstration of the attachment of a specific type of coloured Maillard product to a protein... 

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