Nitrogen, in food

Figure 6a. Plot of river nitrogen export versus net human-derived nitrogen inputs to each of the temperate regions (all European and North American region, except the Western Gulf of Mexico) net inputs are equal to the sum of anthropogenic NOy deposition, fertilizer inputs, nitrogen fixation by crops, and the net import or export of nitrogen in food and feed. (Howarth, 1996).

USE In manuf of ammonia, nitric acid, nitrates, cyanides, etc. in manuf explosives in filling high-temp thermometers, incandescent bulbs to form an inert atm for preservation of materials, for use in dry boxes or glove bags. Liquid nitrogen in food-freezing processes iu the laboratory as a coolant. Pharmaceutic aid (air displacement). Caution In high concns it is a simple asphyxiant. 

MeV neutron activation analysis has been widely employed in the direct determination of oxygen in rocks and of nitrogen in food grains and explosives. Charged-particle activation analysis is useful in the analysis of thin films or coatings on metals. 

All protein determination methods described are not absolute and demand some form of calibration. The Kjeldahl s method remains the only official method currently available for calibration purposes and maintains its position as the most frequently used technique for the determination of organic nitrogen in food products. CE and immunochemical (enzyme-linked immunosorbent assay) techniques are most suitable for rapid separation and quantification of individual food proteins and are promising for widespread use in food protein analysis due to their high sensitivity, specificity, and simplicity of operation. There are numerous methods for the evaluation of the nutritional quality of food proteins. 

I n a titration, we measure the quantity of a known reagent required to react with an unknown sample. From this quantity, we deduce the concentration of analyte in the unknown. Titrations of acids and bases are among the most widespread procedures in chemical analysis. Later in this chapter, we will see how acid-base titrations are used to measure nitrogen in foods, a measure of protein content. 

Jones, D.B. 1941. Factors for converting percentages of nitrogen in foods and feeds into percentages of proteins. Circular No 183, issued August 1931, revised February 1941, United States Department of Agriculture, Washington, DC, 1-21. 

About 85% of all nitrogen in food proteins available for human consumption (21 out of 24.5 Mt N) thus came—directly in plant foods or indirectly in animal products—from the world s cropland. And because synthetic nitrogen fertilizers provided about half (44-51%) of the nutrient in harvested crops, roughly 40% (37-43%) of the world s dietary protein supply in the mid-1990s originated in the Haber-Bosch synthesis of ammonia (fig. 8.1). But this global mean both overestimates and underestimates the degree of our dependence on the Haber-Bosch process because the... 

A ruthenium-based catalyst is used but low yields resulting from unexpected side reactions are stiU a problem. Refinement of alternative route ammonia manufacture and advances in genetic engineering, allowing a wider range of plant life to fix nitrogen in situ should provide assurance for long term world food needs. 

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). 

The dyes on the group above are known as azo dyes, because they have the two nitrogen atoms together in the center (called an azo group). These dyes were originally derived from coal tar, but are now mostly made from petroleum. Azo dyes come in many colors besides those allowed in food (listed above). The other colors find use in fabrics, paper products, and plastics. 

We proposed to study diet and health by combining bone chemistry and histomorphometry. Diet would be determined by analysis of stable isotopes of carbon and nitrogen in bone protein and some preserved hair. In addition, trace elements would be quantitatively analyzed in preserved bone mineral. Abonyi (1993) participated in the study by reconstructing the diet from historical sources and analyzing various foods. Having analyzed human tissues for stable isotopes and trace elements, and foods for the same variables, we hoped to learn more about 19th century diet in southern Ontario, and at the same time, learn more about paleodiet reconstruction. 

Commercially available nonfat dried milk and dried buttermilk have also been shown to contain small but detectable levels of NDMA (, , ). It has been suggested that N-nitrosamine formation is possible in foods that are dried in a direct-fired dryer (65). In such a dryer, the products of combustion come into direct contact with the food being dried, and N-nitrosamine formation is probably due to the reaction between secondary and/or tertiary amines in the food and the oxides of nitrogen that are produced during fuel combusion (65). 

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

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