Benders'dictionary of nutrition and food technology

331nitric oxide (NO) Synthesised in most mammalian cells by theaction of nitric oxide synthetase (EC 1.14.13.39) on arginine.Itcauses vasodilatation and inhibits platelet aggregation (and sohas anticoagulant action), acting by cell surface receptors andintracellular guanylate cyclase (EC 4.6.1.2), leading to increasedformation of cyclic GMP. Before it was identified, NO was knownas the endothelium-derived relaxation factor.nitrites Found in many plant foods, since they are rapidly formedby the reduction of naturally occurring nitrate. Nitrite is theessential agent in preserving meat by pickling, since it inhibitsthe growth of Clostridia; it also combines with the myoglobin ofmeat to form the characteristic red nitrosomyoglobin.See also nitrosamines.nitrogen A gas comprising about 80% of the atmosphere; innutrition the term ‘nitrogen’ is used to refer to ammonium saltsand nitrates utilised as plant fertilisers; proteins and amino acidsas animal nutrients; and urea and ammonium salts as excretoryproducts.nitrogenase The enzyme (EC 1.18.6.1 or 1.19.6.1) in nitrogenfixingmicro-organisms that catalyses the reduction of N 2 toammonia. Irreversibly inactivated by oxygen.See also leghaemoglobin.nitrogen balance (N balance) The difference between the dietaryintake of nitrogen (mainly protein) and its excretion (as urea andother waste products). Healthy adults excrete the same amountas is ingested, and so are in nitrogen equilibrium. During growthand tissue repair (convalescence) the body is in positive Nbalance, i.e. ingestion is greater than loss and there is an increasein the total body pool of nitrogen (protein). In fevers, fasting andwasting diseases (see cachexia) the loss is greater than the intakeand the individual is in negative balance; there is a net loss ofnitrogen from the body.nitrogen conversion factor Factor by which total nitrogen contentof a material (measured chemically, e.g. by the kjeldahl determination)is multiplied to determine the protein; depends on theamino acid composition of the proteins concerned. Wheat andmost cereals 5.8, rice 5.95, soya 5.7, most legumes and nuts 5.3,milk 6.38, other foods 6.25. Errors arise if part of the nitrogen isnon-protein nitrogen. In mixtures of proteins, as in dishes anddiets, the factor of 6.25 is used. Crude protein is defined as N ×6.25.nitrogen equilibrium See nitrogen balance.nitrogen-free extract (NFE) In the analysis of foods and animalfeedingstuffs, the fraction that contains the sugars and starchesplus small amounts of other materials.