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- Carvalho, Raquel N., et al.
(author)
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Mixtures of chemical pollutants at European legislation safety concentrations : how safe are they?
- 2014
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In: Toxicological Sciences. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 141:1, s. 218-233
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Journal article (peer-reviewed)abstract
- The risk posed by complex chemical mixtures in the environment to wildlife and humans is increasingly debated, but has been rarely tested under environmentally relevant scenarios. To address this issue, two mixtures of 14 or 19 substances of concern (pesticides, pharmaceuticals, heavy metals, polyaromatic hydrocarbons, a surfactant, and a plasticizer), each present at its safety limit concentration imposed by the European legislation, were prepared and tested for their toxic effects. The effects of the mixtures were assessed in 35 bioassays, based on 11 organisms representing different trophic levels. A consortium of 16 laboratories was involved in performing the bioassays. The mixtures elicited quantifiable toxic effects on some of the test systems employed, including i) changes in marine microbial composition, ii) microalgae toxicity, iii) immobilization in the crustacean Daphnia magna, iv) fish embryo toxicity, v) impaired frog embryo development, and vi) increased expression on oxidative stress-linked reporter genes. Estrogenic activity close to regulatory safety limit concentrations was uncovered by receptor-binding assays. The results highlight the need of precautionary actions on the assessment of chemical mixtures even in cases where individual toxicants are present at seemingly harmless concentrations.
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- Türk, Maria, 1963
(author)
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Cereal- and Microbial Phytases. Phytate Degradation, Mineral Binding and Absorption
- 1999
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Doctoral thesis (other academic/artistic)abstract
- Cereal foods contain large amounts of phytate (myo-inositol hexaphosphate; IP6), which is the major storage form of phosphorus, in the plant. IP6 possesses a high potential for chelating minerals, such as Fe 2+, Zn2+, Mg2+ and Ca2+. This is of nutritional importance owing to the negative effect on the bioavailability of essential elements from the food. During food processing, IP6 can be completely or partly degraded. Thus, processed foods may contain a mixture of different inositol phosphates, with 6 or fewer phosphate groups, IP6-IP1. This thesis deals with IP6, its degradation during breadmaking, the mineral binding capacity of its degradation products and the effect of cereal- and microbial phytases on IP6 hydrolysis and dietary iron absorption in humans. The binding of metal ions (Cu2+, Zn2+ and Cd2+) to isolated fractions of inositol phosphates (IP6-IP3) was investigated at pH 3-7. All inositol phosphate fractions studied had a pronounced binding capacity at pH 5 - 7. This indicates that mineral complex formation with lower inositol phosphates (IP4, IP3) may occur in the duodenum, which is important from a nutritional point of view if these complexes inhibit mineral absorption. Phytases are phosphatases, capable of hydrolyzing IPV, thus producing inositol phosphates with a lower degree of phosphorylation. The effects of cereal (wheat) and microbial (Aspergillus niger and Saccaromyces cerevisiae) phytases on IP6 hydrolysis were studied in wheat during breadmaking. Activation of endogenous wheat phytase, the addition of Baker's yeast (S. cerevisiae) and, in particular, phytase from A. niger reduced IP6 during breadmaking. A specific method for determining phytase activity by measuring the formation IP5 was developed. As different phytases produce different isomers of IP5, this method can also be used to distinguish between phytases of different origins. Commercial strains of S. cerevisiae proved able to develop phytase activity, i.e. to grow on a synthetic medium with IP6 as the only source of phosphorus. Both strains studied expressed a metabolism well adapted for utilization of phosphorus from IP6. The phytases proved to be of the 3-phytase type, yielding DL-Ins(1,2,4,5,6)P5, DL-Ins(1,2,5,6)P4 and DL-Ins(1,2,6)P3 as degradation products. The potential of wheat phytase and A. niger phytase to improve iron absorption from a meal with phytate was studied in humans using a radioisotope technique. When added to the meal at consumption, endogenous wheat phytase had no effect but A. niger phytase was found to markedly increase iron absorption.
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