Protein nutrition biological value

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). 

The vegetarian should be careful to ensure a balanced ingestion of proteins, fats, carbohydrates, and vitamins. Most animal proteins contain all the essential amino acids however, vegetable proteins often lack one or more of them. Often, plant amino acids are of low biologic value and incompletely digested. Vegans often benefit from nutritional consultation, which would allow the patient to make sure that she ate foods that complemented each other in providing the essential amino acids. 

Proteins are not required for their caloric value, but for their content of amino acids. This presents two nutritional problems (1) Does a food protein contain the correct numbers of types of amino acids (2) How accessible are the amino acids, i.e., how digestible is the food These qualities of a dietary protein are expressed as its biological value. 

The loss of nutritive value when protein or protein-rich foods are heated or stored in the presence of carbohydrates has been studied by a large number of groups (8,10,12,18,29,30). A decrease in the digestibility of proteins and in the availability of amino acids and carbohydrates after the Maillard reaction is shown in Table II. It can be concluded from this that the biologic value of proteins has also decreased. For example, in Table in one can see significant decreases in amino acids of egg albu-t... 

In addition to the nutritional and physiological effects of Maillard browned protein as described in the previous section, it has been shown that the reduced nutritional value of the brown products does not seem to be limited to the loss of amino acids, since supplementation of the diet with those amino acids could not completely restore its biological value (15). This suggests the possible formation of some inhibitory or anti-nutritional compounds during the Maillard reaction, the presence of which cannot be detected with short-term nutritional feeding assays. Moreover, the short-term feeding effects reported in the literature (30) seem to be due in part to nutritional deficiency and not specifically the browning compounds. 

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. 

Oser, B.L. An integrated essential amino acid index for predicting the biological value of proteins. In Protein and amino acid nutrition 66. (Albanese, A.A., ed.). New York Academic Press 1959... 

Since biological value is dependent primarily upon essential amino acid constitution, it would seem logical to assess the nutritive value of a protein by determining its essential amino acid constitution and then comparing this with the known amino acid requirements of a particular class of animal. Application of modern chromatographic techniques coupled with automated procedures allows relatively quick and convenient resolution of mixtures of amino acids. However, the acid hydrolysis used to produce such mixtures from protein destroys practically all the tryptophan and a considerable proportion of the cystine and methionine. Tryptophan has to be released by a separate alkaline hydrolysis, and cystine and methionine have to be oxidised to cysteic acid and methionine sulphone to ensure their quantitative recovery. Losses of amino acids and the production of artefacts, which are greater with foods of high carbohydrate content, are reduced if the hydrolysis is carried out in vacuo. Evaluations of proteins in terms of each individual amino acid would be laborious and inconvenient, and several attempts have been made to state the results of amino acid analyses in a more useful and convenient form. 

A system for the quantitative nutrition of ruminant animals should embody the processes described, which requires that factors such as degradabUity, efficiency of nitrogen captme, microbial protein yield, digestibihty of microbial protein, digestibihty of dietary imdegraded protein and the trae biological value of the absorbed nitrogen or its essential amino acid content be quantified. 

Blood meal is a chocolate-coloured powder with a characteristic smell. It contains about 800 g/kg of protein, small amounts of ash and oil, and about 100 g/kg of water. It is important nutritionally only as a source of protein. Blood meal is one of the richest sources of lysine and a rich source of arginine, methionine, cystine and leucine, but it is deficient in isoleucine and contains less glycine than fish, meat, or meat and bone meals. Owing to the poor balance of amino acids, its biological value is low in addition, it has a low digestibility. It has the advantage, in certain situations, that its protein has a very low rumen degradability (about 0.20). 

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