Proteins biological value

From the analysis of the protein biological values, protein requirements would appear to be satisfied equally well by administering daily 0.53 g of egg powder or 1.12 g of gluten per kilogram of body weight. However, when the requirements are satisfied by large amounts of protein with poor nutritive values, the organism does not function optimally. 

Net protein utilization (NPU) = %digestibility (D) x biological value(BV) complete utilization = 100. Biological value is given in parentheses ... 

Biological value (BV) = % of absorbed nitrogen retained in body tissue complete retention = 100. Data in parentheses for control group, with no single-ceU protein in diet. 

Table 11 presents data on the protein quaUty of a variety of LPC products obtained from rat-feeding studies. Typical protein efficiency ratio (PER) values for LPCs derived from alfalfa range from 1.41 without supplementation to 2.57 with 0.4% methionine added casein can be adjusted to a PER of 2.50 (98,100). Biological values (BV) of mixtures of LPCs, such as barley and rye grass or soybean and alfalfa, maybe higher than either LPC alone. The effect has been attributed to the enhanced biological availabihty of lysine in these mixtures (99). 

Proteins are the major components by bulk in many biological samples and hence the weighing of a dried sample should give an estimate of the amount of protein present. Similarly, solutions that contain protein show values for specific gravity and surface tension which are in some way related to protein content. Measurements of the turbid ity resulting from the precipitation of protein and the absorption of radiation at specif ic wavelengths have all been used quantitatively... 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

Proteins from animal sources Proteins from animal sources (meat, poultry, milk, fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins (Figure 27.18). [Note Gelatin prepared from animal collagen is an exception it has a low biologic value as a result of deficiencies in several essential amino acids.]... 

Combining two incomplete proteins that have complementary amino acid deficiencies results in a mixture with a higher biologic value. 

For example, the UHT heat treatment results in some protein dena-turation, but the biological value and net utilization of milk proteins remain essentially unaffected (Katz et al. 1981 Ford and Thompson 1981 Mehta 1980). In fact, UHT milk may be more digestible than raw or conventionally pasteurized milk because of the greater protein denaturation. The results of both animal feeding studies and studies of human infants indicate that the protein utilization of UHT milk is at least as high as that of conventionally pasteurized milk (Renner 1980 Katz et al. 1981). 

Alternate Protocol 4 Net Protein Utilization (NPU) and Biological Value... 

Net protein ratio (NPR) is used to correct PER values for the amount of protein required for cell maintenance. NPR is often run in conjunction with a PER. The experiment requires that one additional set of animals be added as a treatment group. This group of animals is fed a basal diet with no protein (zero protein or basal diet). Results from RNPR are similar to net protein utilization (NPU) and biological value (BV methods, see Alternate Protocol 4). A 2-week RNPR is thought to be the most appropriate rat test for routine assessment of protein quality. 

Bicinchoninic acid (BCA), total protein determination, 77-104 Bilirubin, in BCA protein assay, 96 Binding, water, see Water retention Biological value (BV), protein quality, 128-129, 133 Biuret assay... 

Protein quality analysis basic protocol, 125-126 biological value (BV), 128-129 diet formula, 137 generally, 133, 135, 137-139 incorporating net protein ratio correction, 126-128... 

PPC is a high-quality product, widely used in the human food industry because of its high digestibility and high biological value of the protein. It is a high-quality protein source suitable for use in all poultry diets. However, its high cost makes its use uneconomical for this purpose. 

This product consists of milk from which most of the fat has been removed but which contains all the protein. The protein has a high biological value and is very digestible. Skim milk is a good source of B vitamins, but the fat-soluble vitamins (A and D) are removed with the fat. Skim milk should either be fresh or always at the same degree of sourness. Attention should be paid to the cleanliness of the equipment used for feeding. Normal bacterial acidification can be used as an effective and convenient method of stabilization. 

Zduhczyk, Z., Juikiewicz, J., Flis, M. and Frejnagel, S. (1996) The chemical composition and nutritive value of low-alkaloid varietiesofwhitelupin.2.Oligosaccharides, phytates, fatty acids and biological value of protein. Journal of Animal and Feed Science 5, 73-82. 

This leads to a decrease in the biological value of the protein. Milk is a good model to study the nutritional effects of the Maillard reaction because of its high levels of lysine and lactose. In processed milks, unavailable lysine is present only as e-deoxylactulosyllysine (9,24) its level which depends on the type of treatment can be measured by the furosine method (24,31). 

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