Protein fractions, composition

Casein. Milk contains proteins and essential amino acids lacking in many other foods. Casein is the principal protein in the skimmed milk (nonfat) portion of milk (3—4% of the weight). After it is removed from the Hquid portion of milk, whey remains. Whey can be denatured by heat treatment of 85°C for 15 minutes. Various protein fractions are identified as a-, P-, and y-casein, and 5-lactoglobulin and blood—semm albumin, each having specific characteristics for various uses. Table 21 gives the concentration and composition of milk proteins. 

The composition of body fluids remains relatively constant despite the many demands placed on the body each day. On occasion, these demands cannot be met, and electrolytes and fluids must be given in an attempt to restore equilibrium. The solutions used in the management of body fluids discussed in this chapter include blood plasma, plasma protein fractions, protein substrates, energy substrates, plasma proteins, electrolytes, and miscellaneous replacement fluids. Electrolytes are electrically charged particles (ions) that are essential for normal cell function and are involved in various metabolic activities. This chapter discusses the use of electrolytes to replace one or more electrolytes that may be lost by the body. The last section of this chapter gives a brief overview of total parenteral nutrition (TPN). 

Table X. Amino Acid Compositions of Acid Hydrolyzed Protein Fractions from DMSO and Aqueous Extracts of Pondweed and Water Spinach3...

HPLC analysis of food proteins and peptides can be performed for different purposes to characterize food, to detect frauds, to assess the severity of thermal treatments, etc. To detect and/or quantify protein and peptide components in foods, a number of different analytical techniques (chromatography, electrophoresis, mass spectrometry, immunology) have been used, either alone or in combination. The main advantages of HPLC analysis lie in its high resolution power and versatility. In a single chromatographic run, it is possible to obtain both the composition and the amount of the protein fraction and analysis can be automated. 

Cerbulis, J. and Farrell, H. M., Jr. 1975. Composition of milks of dairy cattle. I. Protein, lactose, and fat contents and distribution of protein fraction. J. Dairy Sci. 58, 817-827. 

Kondratyeva, T.P. (1977). Changes in total protein content and the composition of protein fractions in the blood serum of some Black Sea fish during the spawning season (In Russian). Gydmbiologicheskii Zhumal 13,75-79. 

The results are shown diagramatically in Figure 5. The left bar shows the analytical breakdown of 100 mg. of exponential cell substance. Protein of the cytoplasm is shown in white and the area corresponding to the protein moiety of the membrane lipoprotein is marked by vertical dashed lines. The sum of these two protein fractions is nearly the same in all three instances. This is to be expected, since the total amount of bacterial protein cannot increase further after one of the protein-essential nutrients has been used up. The left bar shows the calculated composition of an exponentially growing culture at the depletion point, whether the depleted nutrient is valine, threonine, or any other nutrient. The center bar shows the total amount of bacterial... 

Another interesting aspect of the low-temperature procedure must be borne in mind if the different types of forces act so as to counterbalance one another, changes in solvent composition and temperature would lead to new favorable or unwanted separation patterns. In such cases, besides the practical interest of the procedure for protein fractionation, a better understanding of the types of forces involved in protein association, and their relative contributions, could result from systematic studies of unexpected side effects. This could make them the basis for new separation procedures. 

Prakash, D. and Pal, M. (1998). Chenopodium Seed protein, fractionation and amino acid composition. Int. J. Food Sci. Nutr. 49, 271-275. 

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