Protein content of foods

Proteins are constantly being lost via the intestine and, to a lesser extent, via the kidneys. To balance these inevitable losses, at least 30 g of protein have to be taken up with food every day. Although this minimum value is barely reached in some countries, in the industrial nations the protein content of food is usually much higher than necessary. As it is not possible to store amino acids, up to 100 g of excess amino acids per day are used for biosynthesis or degraded in the liver in this situation. The nitrogen from this excess is converted into urea (see p. 182) and excreted in the urine in this form. The carbon skeletons are used to synthesize carbohydrates or lipids (see p. 180), or are used to form ATP. 

Activation with 14 MeV neutrons has been used to determine the oxygen content of various metals such as beryllium 20>, Cl, F, O, Na, Si, and various rare earths in complex molten salt electrolytes 45>, the protein content of food products by means of the nitrogen content 46>, i60/180 and 14N/15N isotopic ratios in stable isotope tracer experiments 47,48), and in a wide variety of other applications. One application we... 

Wood, D. E., P. L. Jessen, and R. E. Wood Industrial Application of Fast Neutron Activation Analysis for Protein Content of Food Products. Paper presented at the 52nd Annual Meeting of the American Association of Cereal Chemists, Los Angeles, California, April, 1967. 

Low-protein recipes from cookbooks designed for PKU can be useful for MSUD as well. The leucine content can be estimated from the protein content of foods (60 mg leucine per gram of protein). For older individuals with MSUD, counting protein rather than leucine may be appropriate and easier for the patient, if metabolic control can be maintained with this less accurate method. 

The metabolisable protein content of a food is of no use as a guide to the food s ability to satisfy the residual demand for metabolisable protein, since it includes a contribution from ERDP, which has already been taken into account in the form of DMP. The protein content of foods is thus stated in terms of ERDP and DUP. 

The protein content of plant foods is most of the time so different from that of animal-derived foods that large amounts of plants will have to be consumed with relatively little effect on consumer 5 N values. For an archaeologically meaningful interpretation of isotopic measurements this weighting problem needs to be considered. 

Dairy proteins can be used to boost the protein content of sfarch-based puffed snacks made from cornmeal fhey bind wafer and form doughy pastes with the starch, but not the non-TWPs. A wide possibility exists for creating new foods wifh fexfurized dairy proteins due to the availability of an extensive range of achievable sfates (Onwulafa et ah, 2010). 

The Folin-Ciocalteu assay is the most widely used method to determine the total content of food phenolics (Fleck and others 2008). Folin-Ciocalteu reagent is not specific and detects all phenolic groups found in extracts, including those found in extractable proteins. A disadvantage of this assay is the interference of reducing substances, such as ascorbic acid (Singleton and others 1999). The content of phenolics is expressed as gallic acid or catechin equivalents. 

The original applications of NIR were in the food and agricultural industries where the routine determination of the moisture content of foodstuffs, the protein content of grain and the fat content of edible oils and meats at the 1% level and above are typical examples. The range of industries now using the technique is much wider and includes pharmaceutical, polymer, adhesives and textile companies. The first in particular are employing NIR spectrometry for the quality control of raw materials and intermediates and to check on actives and excipients in formulated products. Figure 9.26(b) demonstrates that even subtle differences between the NIR spectra of enantiomers can be detected. 

Protein contents of selected oilseeds and legume seeds, and food protein ingredients prepared by various procedures, are shown in Table I. Amino acid contents and protein efficiency ratios (PER s)... 

FAO, "Amino Acid Content of Foods and Biol. Data on Protein, "U.N. Food and Agriculture Organization, Rome, 1970. 

In contrast, the whey proteins are relatively small globular proteins. a-Lactalbumin represents about 20 % of the protein content of bovine whey (3.5 % of total bovine milk protein), and it is the principal protein in human milk (Brew and Grobler, 1992). Nanotube assembly has been discovered in some solutions containing a hydrolysed derivative of this protein. And it appears that the a-lactalbumin nanotube is unique in the sense that it is the only artificial nanotube that has so far been made from a food protein (Graveland-Bikker et al., 2004 Graveland-Bikker and de Kruif, 2006). As for p-lactoglobulin, it has the capacity under certain specific conditions to form nano-fibres in aqueous media (as can various other globular food proteins, such as ovalbumin, soy proteins, and bovine serum albumin) (van der Linden, 2006 Nicolai, 2007). 

Emulsification properties. Caseins and caseinates are commonly selected for food product applications that require surfactant properties, e.g., emulsification and foam stabilization, since they contain high protein contents of > 90 %, are highly soluble, and are resistant to heat-induced denaturatlon in products to be subjected to high temperature processing conditions (15). 

Food and Agriculture Organization of the United Nations. Food Policy and Food Science Service Nutrition Division. 1970. Amino acid content of foods and biological data on proteins. FAO Nutritional Studies No. 24, Rome. 

Vanderzant, C. and Tennison, W. R. 1961. Estimation of the protein content of milk by dye binding with buffalo black. Food Technol. 15 63-66. 

In terms of percentage of protein content of basic sources, the animal sources far excel the plant sources. For example, the protein content of some typical unfortified foods is as follows 20-30% for cooked poultry and meats 19-30% for cooked or canned fish 25% for cheese 13-17% 17% for cottage cheese 16% for nuts 13% for whole eggs 7-14% for dry cereals 8.5-9% for white bread 7-8% for cooked legumes and about 2% for cooked cereals. 

Diets are isocaloric. The composition of the test and control (reference protein) diet (calculated on a dry weight basis) is 10% protein (1.6% nitrogen), 1 % AIN vitamin mix 76,3.5% AIN mineral mixture 76 (Nutritional Biochemicals), 0.2% choline bitartrate, 5% cellulose (only if test food is <5% total dietary fiber), corn oil to 10% total fat, and corn starch to total 100%. To account for differences in the protein content of the test diet, the level of corn starch can be adjusted (Joint FAO/WHO Expert Consultation, 1991). The chemical composition (proximate analysis) of the test protein must be measured before test diets are formulated. The proximate analysis of the test and control diets are to be measured after the diets are formulated, but before they are fed, to ensure that the protein content is the same for all diets, and that the diets are isocaloric. 

The estimates for the caloric content of food are 9.0Cal/g for fats, and 5.0Cal/g for carbohydrates and proteins. A breakfast muffin contains 14% by weight of fat, 64% carbohydrate, and 7% protein (the rest is water, which has no calories). Does it meet the criterion of 30% or less calories from fat, which is recommended for the U.S. population ... 

B14. Berger, H., and Antener, I., Influence of protein content of the food upon the excretion of free a-aminonitrogen in the urine as a measure of aminoaciduria. Intern. Z. Vitaminforsch. 28, 17-32 (1957). 

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