Storage trace elements

PLANT UPTAKE, STORAGE, TRANSLOCATION, AND CONTENTS OF TRACE ELEMENTS... 

The content of trace elements in foods depends on their concentration in the raw materials and additives used in food production. In addition, trace elements may be transmitted to food from the equipment used during food processing and from the packaging material during storage. 

Iron (Fe) is quantitatively the most important trace element (see p. 362). The human body contains 4-5 g iron, which is almost exclusively present in protein-bound form. Approximately three-quarters of the total amount is found in heme proteins (see pp. 106,192), mainly hemoglobin and myoglobin. About 1% of the iron is bound in iron-sulfur clusters (see p. 106), which function as cofactors in the respiratory chain, in photosynthesis, and in other redox chains. The remainder consists of iron in transport and storage proteins (transferrin, ferritin see B). 

Storage. The liver not only stores energy reserves and nutrients for the body, but also certain mineral substances, trace elements, and vitamins, including iron, retinol, and vitamins A, D, K, folic acid, and Bi2. 

As the human body is able to store many minerals, deviations from the daily ration are balanced out over a given period of time. Minerals stored in the body include water, which is distributed throughout the whole body calcium, stored in the form of apatite in the bones (see p. 340) iodine, stored as thyroglobulin in the thyroid and iron, stored in the form of ferritin and hemosiderin in the bone marrow, spleen, and liver (see p. 286). The storage site for many trace elements is the liver. In many cases, the metabolism of minerals is regulated by hormones—for example, the uptake and excretion of H2O, Na, ... 

Stoeppler, M. Analytical aspects of sample collection, sample storage and sample pretreatment, in Trace Element Analytical Chemistry in Medicine and Biology (ed.) Bratter, P. and Schramel, P., Vol. 2, p. 909, Berlin—New York, Walter de Gruyter Co 1983... 

Reviews on the stability and storage of individual trace elements have been made by several... 

Folate is a relatively unstable nutrient processing and storage conditions that promote oxidation are of particular concern since some of the forms of folate found in foods are easily oxidized. The reduced forms of folate (dihydro- and tetrahydrofolate) are oxidized to p-aminobenzoylglutamic acid and pterin-6-carboxylic acid, with a concomitant loss in vitamin activity. 5-Methyl-H4 folate can also be oxidized. Antioxidants (particularly ascorbic acid in the context of milk) can protect folate against destruction. The rate of the oxidative degradation of folate in foods depends on the derivative present and the food itself, particularly its pH, buffering capacity and concentration of catalytic trace elements and antioxidants. 

If vitamins are added to a product to make a nutritional claim, it is critical that shelf-life studies are undertaken to prove that the overages added are sufficient to ensure that the label claims can be met at the end of product shelf life. This is important as none of the vitamins are fully stable in a soft drink environment and some, for instance vitamin C, are very quickly lost in the presence of oxygen. The addition of the fat-soluble vitamins to a soft drink also offers a formulation challenge to ensure that they are fully dispersed and that there are no problems with neck ringing during storage. Trace metals, particularly the transition elements, can also have a deleterious effect on vitamin shelf life, and sometimes metal scavengers, such as EDTA or phosphate salts, are added to improve the shelf life. 

Aitio, A. and Jarvisalo, J. (1994) Sampling and sample storage. In Techniques and Instrumentation in Analytical Chemistry, Vol. 15, Trace Element Analysis in Biological Specimens (eds Herber, R.F.M. and Stoeppler, M.). Elsevier, Amsterdam. 

As detailed in the earlier chapter on milk, from an analytical viewpoint the total determination of trace elements in human milk samples as such is still an open issue because decomposition, preconcentration, and storage of trace analytes in solutions are often a source of concern. The accuracy of the analytical results can, in fact, be endangered by these pretreatments. There are relatively few methods for such total direct analytical determinations, and in many cases they are still inadequate to meet the needs of the analyst. 

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