Nutrient requirements Trace minerals

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

Other Nutrients - Minerals, vitamins, and trace minerals are also required in most fermentations. 

For some nutrients, such as the vitamins biotin (section 11.12) and pantothenic acid (section 11.13), and a number of trace minerals, deficiency is unknown except under experimental conditions. For these nutrients there are no estimates of average requirements, and therefore no reference intakes. As deficiency does not occur, it is obvious that average levels of intake are more than adequate to meet requirements. For these nutrients there is a range of intakes that is defined as safe and adequate, based on the observed range of intakes. 

While the trace-element content of guano and, to a lesser extent, of mined mineral salts, could make some contribution to the nutrient requirements of crops, these materials are no longer adequately available. We have now become largely dependent on highly purified compound fertilisers containing only nitrogen, phosphorus and potassium as nutrients, so that the rate of depletion of essential trace elements has been greatly accelerated. The natural cycle... 

The essential mineral nutrients are classified either as principal elements or as trace and ultratrace elements. The distinction between these groups is the relative amounts ia the dietary requirement (see Table 1). 

Water accounts for over half the body mass (55%) of the average human. Of the remaining 45%, 19% is protein, 19% is lipid, less than 1% is carbohydrate, and 7% is inorganic material. Nutrients must contain the raw materials that go into the construction of the components of the human body. In addition, nutrients must supply the necessary chemical energy and enzyme cofactors (vitamins and trace metal elements) that are required for the maintenance and growth of the human body. The human body requires nutrients such as water, amino acids, fats, carbohydrates, and major minerals in large amounts. Vitamins and trace metal elements are required in smaller amounts. 

Also, it has long been known that mineral nutrients are essential to the life and continued health of poultry and livestock. The latter often require supplementary P, Ca, and NaCl. Laying hens require a diet that is very high in Ca. Much progress has been made in recent years toward understanding the nutritional needs of poultry and livestock, particularly the role played by trace elements. 

The rate of growth and reproduction of organisms depends not only upon the availability of carbon, water and energy but also upon a variety of essential mineral nutrients. In Chapter 2 we saw that a number of elements are important, such as N in chlorophyll and amino acids, P in ATP and phospholipids, Si in diatom tests and Ca in coccoliths. Some of these essential elements (e.g. N, P, Ca and Si) are generally abundant, and so can be termed macronutrients, whereas others (e.g. Fe and Mg) are required by organisms in only trace amounts and are called micronutrients. 

The many mineral interactions which influence the safe dietary levels of essential and toxic elements are partly represented in Figure 3.2. While interactions involving dietary elements may be either detrimental or beneficial, the major concern is that an antagonistic element may induce a deficiency of its counterpart nutrient whose concentration in the diet is borderline. The assessment of such in-vivo interactions will be considered here under the limits of bioavailability, which occurs at the site of absorption in the intestinal mucosa or the redistribution from one tissue to another one. Figure 3.2 illustrates the most important, quite different, species-specific interactions of metals, trace and macro elements, respectively, with net requirements in animals and man. Clearly, there are interrelationships in the metabolism of the mineral elements consumed. 

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