Proteins in foods

Use of some oilseed proteins in foods is limited by flavor, color, and flatus effects. Raw soybeans, for example, taste grassy, beany, and bitter. Even after processing, residues of these flavors may limit the amounts of soybean proteins that can be added to a given food (87). The use of cottonseed and sunflower seed flours is restricted by the color imparted by gossypol and phenoHc acids, respectively. Flatus production by defatted soy flours has been attributed to raffinose and stachyose, which are removed by processing the flours into concentrates and isolates (88). 

The proteins in food supplements are often hydrolyzed to short peptides to make them easier to absorb. A high content of amino acids is deleterious, however. Thus, there is ongoing interest in determining the size distribution of peptides in protein hydrolyzates. Silvestre et al. (29,30) used a PolyHEA column to compare casein hydrolyzates prepared through various methods. They were able to assess the content of the smallest peptides, as well as amino acids (Fig. 8.13). 

Animals, including humans, cannot synthesise all the different amino adds they need and thus require them in their diet. These amino adds are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animal s cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitrogen from the soil (as nitrate) with organic molecules derived from carbon from the atmosphere (as CO2). 

Proteins in Food Processing, ed. R. Y. Yada, Woodhead Publishing, Cambridge, 2004. 

Kimber, I. and Dearman, R.J., Approaches to the assessment of the allergenic potential of novel proteins in food from genetically modified crops. Toxiol. Sci., 68, 4, 2002. 

Barnes, R.M., IgG and IgA antibodies to dietary proteins in food allergy and tolerance. Clin. Exp. Allergy, 25, S7-S9, 1995... 

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

Sikorski, Z.E. (2002). Chemical reactions of proteins in food systems, in Sikorski, Z.E., ed.. Chemical and Functional Properties of Food Proteins, CRC Press, Boca Raton, 191-216. 

There are four sources of amino acids that enter the free amino acid pool in the body proteins in food proteins secreted into the stomach and intestine by the digestive glands endogenous proteins and microorganisms that die and release their protein in the colon. 

Particularly suitable for insoluble proteins, protein in foods and protein covalently immobilized on chromatographic supports. 

The following factors appear to control the emulsification properties of milk proteins in food product applications 1) the physico-chemical state of the proteins as influenced by pH, Ca and other polyvalent ions, denaturation, aggregation, enzyme modification, and conditions used to produce the emulsion 2) composition and processing conditions with respect to lipid-protein ratio, chemical emulsifiers, physical state of the fat phase, ionic activities, pH, and viscosity of the dispersion phase surrounding the fat globules and 3) the sequence and process for incorporating the respective components of the emulsion and for forming the emulsion. 

Kinsella Q) reviewed the principal categories of functional properties of proteins in foods and outlined various factors affecting them from the point of view of the food chemist and technologist. 

The functional properties that govern the role of proteins in food applications are color flavor texturization solubility viscosity adhesion or cohesion gelation coagulation aeration or foamability water and oil absorption and emulsification. 

Humans have no dietary requirement for protein, per se, but, the protein in food does provide essential amino acids (see Figure 20.2, p. 260). Ten of the twenty amino acids needed for the synthesis of body proteins are essential—that is, they cannot be synthesized in humans at an adequate rate. Of these ten, eight are essential at all times, whereas two (arginine and histidine) are required only during periods of rapid tissue growth characteristic of childhood or recovery from illness. 

Lin, C. F. 1977. Interaction of sulfated polysaccharides with proteins. In Food Colloids. H.D. Graham (Editor). AVI Publishing Co., Westport, Conn. 

Law, B. A. 1982. Microbial proteolysis of milk proteins. In Food Proteins. P. F. Fox and J. J. Condon (Editors). Applied Science Publishers, New York, pp. 307-328. 

Several essential amino acids have been shown to be the limiting factor of nutrition in plant proteins. In advanced countries, the ratio of vegetable proteins to animal proteins in foods is 1.4 1. In underdeveloped nations, the ratio is 3.5 1. which means that people in underdeveloped areas depend upon vegetable proteins. Among vegetable staple foods, wheat easily can be fortified. It is used as flour all over the world. L-Lysine hydrochloride (0,2% ) is added to the flour. Wheat bread fortified with lysine is used in several areas of the woilcl in Japan it is supplied as a school ration. 

PER is a method to metabolize or determine the quality of protein in foods. Quality is measured by the amount of usable protein and the growth resulting from it through an animal assay. Formerly, this method was used as the standard method for all protein quality analysis. However, there is some question as to whether or not it is a valid measurement. This is because PER does not account for the differences in amino acid requirements between humans and rats (Seligson and Mackey, 1984), nor does PER account for the protein needed for cell maintenance. Therefore, PER results often overestimate the requirements for some amino acids and underestimate others. Specifically, PER tends to underestimate the protein quality of lysine-deficient proteins such as wheat gluten (Hackler, 1977). 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

Kinsella, J.E. 1976. Functional properties of proteins in foods A survey. CRC Crit. Rev. Food Sci. Nulr. (1976) 219-280. 

Mangino, M.E. 1989. Molecular properties and functionality of proteins in food emulsions. In Food Proteins (J.E. Kinsella and W.G. Soucie, eds.) pp. 157-177. American Oil Chemists Society, Champaign, 111. 

Table 2 Functional Roles of Food Proteins in Food Systems...

Table 11 Reason for Determination of Cereal Proteins in Foods and Food Products...

JE Kinsella, S Damodaran. Nutritional, chemical, and physical criteria affecting the use and acceptability of proteins in foods. In J Solms, RL Hall, eds. Criteria of Food Acceptance. Zurich Forster, 1981, pp 296-332. 

Hefle, S.L., Bush, R.K., Yunginger, J.W., and Chu, F.S. 1994. A sandwich enzyme linked immunosorbent assay (ELISA) for the quantitation of selected peanut proteins in foods. J Food Protect 57 419 -23. 

Comparable IgE responses to allergenic proteins in foods as found in patients... 

Globular storage proteins generally exhibit remarkable stability, especially thermal stability, which is common for proteins of the cupin superfamily. Globulins all share the tendency to form large thermally induced aggregates (heat-set gels), which form the basis of the widespread utilization of soy protein in foods (Mills et al. 2002). 

Corporation, Lansing, MI) is a sandwich ELISA used for the quantitative analysis of minimally processed soy flour protein in food products such as cookies, crackers, chocolate bars, and cereals in the range of 2.5-25mg/kg. 

The effective utilization of proteins in food systems is dependent on tailoring the protein s functional characteristics to meet the complex needs of the manufactured food products. Many food proteins require modification to improve such functional properties as solubility, foaming and emulsifying activity (EA). Reviews on classical food protein modifications for improved functionality are available in the literature (Means and Feeney, 1971 Feeney and Whitaker, 1977, 1982, 1986). 

One of the most important factors that determine whether or not a protein is usable in the fabrication of a food product is its functionality. The functionality results from a combination of physico-chemical properties that define the behavior of the food protein in food systems. It is evident that a detailed understanding of food protein functionality requires an intimate knowledge of the protein structure. The bovine milk protein system has been studied in great detail. Although providing useful structure-function... 

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