<p>Minerals and trace elements play essential roles in numerous biochemical and physiological processes in animals and man. A deficiency, an overdose or imbalances between minerals or trace elements will exert a negative effect on health. Generally, it is not the ingested dose of minerals and trace elements that is important to maintain balance, but rather the amount that is bioavailable (available for biological and biochemical processes in the organism). Several food components are able to form soluble or insoluble complexes with minerals and trace elements under gastrointestinal conditions. These food components thereby increase or decrease the availability for absorption in the small intestine, and thus the bioavailability of minerals and trace elements, Due to the complexity of food products, however, the relative contributions of food components to the bioavailability of minerals and trace elements are often not clear.<p>Although in vivo experiments are the best way to study the bioavailability of minerals and trace elements, in vitro methods offer an appealing alternative because they are relatively simple, rapid and inexpensive. Therefore, there is a great need in human nutrition and animal nutrition for an in vitro method which predicts the bioavailability of minerals and trace elements in vivo.<p>Part I describes the scope and the objectives (Chapter 1), and the experimental approach (Chapter 2) of the research presented in this thesis. The objectives were twofold:<br/>- to develop an in vitro method for the prediction of the bioavailability of calcium, magnesium, iron, copper and zinc<br/>- to investigate the effects of phytic acid, dietary fibre and other food components on the in vitro availability of calcium, magnesium, iron, copper and zinc.<br/>To meet these objectives a multidisciplinary approach was followed.<p>Part II discusses several aspects of dietary fibre.<br/>In Chapter 3 a literature review of the definitions and terminology of dietary fibre is presented. Although the term "dietary fibre" is now widely accepted, there is still some confusion concerning its definition.<p>Chapter 4 presents a literature review of methods for the analysis of dietary fibre. As such methods are based on a definition of dietary fibre, it is important that there is consensus regarding the type of components that should be included in the definition. An advantage of a definition based on chemically defined components is that it allows for a specific analytical determination of dietary fibre components.<p>In Chapter 5 a comparison of different methods for the analysis of dietary fibre is presented. The ADF, NDF, Hellendoorn, AOAC and Englyst methods are compared with respect to the amount and the composition of the dietary fibre analysed. Although different methods for the analysis of dietary fibre can yield comparable integral values, the NSP (non-starch polysaccharides) composition of the dietary fibre residues may differ greatly. It is shown that modern methods such as the AOAC and Englyst methods give more accurate determinations of dietary fibre than older methods such as the ADF/NDF method and Hellendoorn's method. Methods in which the NSP are determined (such as the Englyst method) are to be preferred because a well defined group of dietary fibre components are determined. Moreover, the gas chromatographic procedures give insight into the types of NSP present.<p>Part III concerns the analysis of phytic acid (myoinositol hexakis(dihydrogen)phosphate).<br/>A literature review of methods for the analysis of phytic acid is presented in Chapter 6. According to the literature, few methods for the analysis of phytic acid are specific because of interferences from lower inositol phosphates, inorganic phosphates and metal ions. Currently, methods based on anion-exchange chromatography with postcolumn derivatization and methods based on phosphorus-31 NMR show the best results.<p>In Chapter 7 an improved method for the determination of phytic acid is presented. The method is based on an anion-exchange chromatographic procedure with postcolumn derivatization in which EDTA treatment of the samples is incorporated to eliminate interferences from metal ions. The improved method is compared with a HPLC method without EDTA treatment and with a method using small single-use ionexchange columns. It is shown that elimination of the interference of metal ions by means of EDTA treatment in the anion- exchange chromatographic procedure allows for a more specific determination of phytic acid.<p>Part IV deals with in vitro methods for the prediction of the bioavailability of Ca, Mg, Fe, Cu and Zn.<br/>Chapter 8 presents a literature review of in vitro methods for the estimation of the bioavailability and its correlation with bioavailability in vivo. According to the literature, the most promising in vitro methods are based on equilibrium dialysis under simulated physiological conditions, in which the dialysability of minerals and trace elements is taken as a measure for their bioavailability.<p>In Chapter 9 a continuous in vitro method for the estimation of the bioavailability of Ca, Mg, Fe, Cu and Zn is described. In this in vitro method dialysable components (including minerals and trace elements) are continuously removed from the pancreatic digestion mixture. The in vitro method based on continuous dialysis is compared with the in vitro method based on equilibrium dialysis with respect to the dialysability of Ca, Mg, Fe, Cu and Zn from eight types of bread. The continuous in vitro method generally results in higher dialysabilities of minerals and trace elements than the equilibrium in vitro method. The relevance of this effect for prediction of the bioavailability in vivo needs further investigation.<p>The in vitro method with continuous dialysis and the in vitro method with equilibrium dialysis were validated for their usefulness as predictors of the bioavailability of Ca, Mg, Fe, Cu and Zn in an in vivo experiment with piglets. This study is presented in Chapter 10. It is shown that although both in vitro methods show a discrepancy between the absolute values of the availability determined in vitro and the bioavailability determined in vivo, they reflect quite well the effects of differences in food composition on the bioavailability in vivo. Therefore it is concluded that the in vitro methods can be used for a relative prediction of the bioavailability of minerals and trace elements and thus may be very useful in providing preliminary or additional information to in vivo experiments.<p>Part V discusses the influence of food components on the availability of minerals and trace elements.<br/>Chapter 11 is a literature review of the influence of dietary fibre, phytic acid and other food components on the availability of Ca, Mg, Fe, Cu and Zn. This concise review shows that the bioavailability of minerals and trace elements is a very complex issue because it may be influenced by a variety of dietary components. Therefore, the influence of dietary fibre, phytic acid and other dietary components on the bioavailability of minerals and trace elements should not be studied separately but in the whole food matrix.<p>Chapter 12 describes a mathematical model to investigate the relative influences of food components on the in vitro availability of Ca, Mg, Fe, Cu and Zn. The mathematical model is based on chemical theoretical assumptions and optimized with respect to the model structure and the numerical model parameters. It is shown that the mathematical model describes and predicts the in vitro availability of Ca, Mg, Fe and Zn quite well on the basis of the concentrations of two or three food components. The mathematical model proves also valuable for obtaining insight into the relative influences of food components on the in vitro availability of minerals and trace elements. According to the mathematical description of the in vitro availability, phytic acid has a strong negative effect on the availability of Ca, Fe and Zn, and a less pronounced effect on the availability of Mg. Arabinose-containing components decrease the availability of Ca and Fe. Oxalic acid has a negative influence on the availability of Ca, Mg and Zn. Ascorbic acid increases the availability of Fe, while citric acid has a positive influence on the availability of Ca, Mg and Zn. It is shown that food components with a positive influence on availability can counteract the effects of food components with a negative influence.<p>Because in vitro methods are rapid and relatively inexpensive, and mathematical models provide insight into the relative influences of food components, the combination of in vivo experiments, in vitro experiments and mathematical modelling is a powerful approach to obtain a better understanding of the, mechanisms and important factors involved in the bioavailability of minerals and trace elements.<p>The studies presented in this thesis investigated the bioavailability of minerals and trace elements from different points of view. In Part VI the most relevant points of discussion (Chapter 13) and conclusions (Chapter 14) are presented.
|Qualification||Doctor of Philosophy|
|Award date||2 Nov 1992|
|Place of Publication||S.l.|
|Publication status||Published - 1992|
- phytic acid
- dietary fibres