Quality plant proteins

Biological effects of plant proteins on human health have attracted wide attention in the recent past because of the presence of various anti nutrients such as trypsin inhibitors, hemagglutinins, and toxic principles U). Adequate cooking and/or processing inactivates these materials and can improve the quality... 

Soy proteins are used extensively in meat and meat products by the military, the school lunch program and consumers to save money. Their ultimate acceptability is equally dependent upon the nutritional, chemical, sensory and shelf life changes which occur when they are added. Soy proteins in meat products such as ground beef inhibit rancidity, improve tenderness, increase moisture retention, decrease cooking shrink, fat dispersion during cooking and have no important effect on microbiological condition. Concomittantly, inordinate amounts of added soy protein may cause the meat product to be too soft, exhibit an undesirable flavor and may lead to a decreased PER and a deficiency in B-vitamins and trace minerals. In emulsified meat products, soy protein effectively binds water but does not emulsify fat as well as salt soluble muscle protein. Prudent incorporation of plant proteins can result in an improvement of the quality of the meat product with inconsequential adverse effects. 

For example, the color of fresh fruit indicates ripeness and the time the fruit is most likely to taste best. Off-colors in cheese or meats are associated with poor flavor quality. Generally, we expect each food product to have a certain color. Deviations from this expected color can result in rejection of a product even when this color does not adversely influence the flavor or nutritional value of the food. If plant-protein products are to attain widespread utilization in food applications, the color they impart to the product must be considered an important factor in consumer acceptability. 

Amino acids joined together by peptide bonds form the primary structure of proteins. The amino acid composition establishes the nature of secondary and tertiary structures. These, in turn, significantly influence the functional properties of food proteins and their behavior during processing. Of the 20 amino acids, only about half are essential for human nutrition. The amounts of these essential amino acids present in a protein and their availability determine the nutritional quality of the protein. In general, animal proteins are of higher quality than plant proteins. Plant... 

K17. Klein, M. P., mid Kramer, L. N., Estimation of protein quantity and quality by X-ray photoelectron spectroscopy. Improving Plant Proteins Nucl. Tech., Proc. Conf. IAEA, Vienna pp. 243-252 (1970). 

The mixed quality of proteins in the diet The values for protein, noted earlier, refer to high-quality proteins such as those foimd in eggs, fish, and meat. In the real world, the diet contains a mixture of proteins from plant and animal sources. The mixed quality of the proteins, as determined by their component amino acids as well as their variable digestibility, suggests a correction factor in the calculation of the RDA for protein. With this correction, a protein requirement of about 0.64 g protein/kg body weight is calculated. 

The dry mass of pulse seeds consists of saccharides (14—63%), proteins (28 44%), and lipids (1-50%). The other constituents are mineral elements (mainly K and P) and vitamins from the B group. Soybean is the most valuable pod plant, due to its high quantity and good quality of protein. Soy products in the form of meat extenders and analogs are used all over the world. Soybean is also a raw material in the oil industry. 

Rice bran is the outer brown layer, including the rice germ, removed during milling of brown rice to produce white rice. Rice bran is rich in high quality protein, B vitamins, and oil (5). Rice bran represents an underutilized and potentially inexpensive and plentiful source of plant protein for production of HVPs having unique amino acid profiles and flavor characteristics. 

Dietary protein sources differ widely in their proportions of the EAA. In general, complete proteins (those containing sufficient quantities of EAA) are of animal origin (e.g., meat, milk, and eggs). Plant proteins often lack one or more EAA. For example, gliadin (wheat protein) has insufficient amounts of lysine, and zein (com protein) is low in both lysine and tryptophan. Because plant proteins differ in their amino acid compositions, plant foods can provide a high-quality source of essential amino acids only if they are eaten in appropriate combinations. One such combination includes beans (low in methionine) and cereal grains (low in lysine). 

The biological value of food proteins is greatly influenced by the ratio of their essential amino acids. Most food proteins, first of all plant proteins, are deficient in some essential amino acids. The limiting essential amino acid in legume and milk proteins is methionine, and in cereal proteins it is lysine. Beside the knowledge of the requirements of quality and composition of amino acids, it is equally important to know whether these amino acids can be best utilized as free amino acids, in the form of peptides or proteins. The following possibilities exist for improving the balance of essential amino acids in the proteins ... 

The greatest limitation of functional cloning is the design of effective enzyme assays that can rapidly assess the function of thousands of clones. Unfortunately, relatively few metabolic enzymes yield a colored product that can be easily detected. Furthermore, many biosynthetic enzymes act on unavailable, miknown or imstable biosynthetic intermediates that are not suitable for an in vitro enzyme assay. The plant enzymes must also be expressed in active form in E. coli or yeast for accurate functional assessment, and some plant proteins can only be functionally expressed in insect or plant cells, which are not amenable for this functional expression strategy. Finally, expression cloning requires exceptionally high quality cDNA that consists of full-length clones. 

---