Chemical contaminants that are present in food pose a health problem and their levels are controlled by national and international food safety organizations. Despite increasing regulation, foods that exceed legal limits reach the market. In Europe, the number of notifications of chemical contamination due to pesticide residues, mycotoxins and metals is particularly high. Moreover, in many parts of the world, drinking water contains high levels of chemical contaminants owing to geogenic or anthropogenic causes. Elimination of chemical contaminants from water and especially from food is quite complex. Drastic treatments are usually required, which can modify the food matrix or involve changes in the forms of cultivation and production of the food products. These modifications often make these treatments unfeasible. In recent years, efforts have been made to develop strategies based on the use of components of natural origin to reduce the quantity of contaminants in foods and drinking water, and to reduce the quantity that reaches the bloodstream after ingestion, and thus, their toxicity. This review provides a summary of the existing literature on strategies based on the use of lactic acid bacteria or yeasts belonging to the genus Saccharomyces that are employed in food industry or for dietary purposes.

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Mercury in food is present in either inorganic [Hg(II)] or methylmercury (CHHg) form. Intestinal absorption of mercury is influenced by interactions with other food components. The use of dietary components to reduce mercury bioavailability has been previously proposed. The aim of this work is to explore the use of lactic acid bacteria to reduce the amount of mercury solubilized after gastrointestinal digestion and available for absorption (bioaccessibility). Ten strains were tested by addition to aqueous solutions containing Hg(II) or CHHg, or to food samples, and submission of the mixtures to gastrointestinal digestion. All of the strains assayed reduce the soluble fraction from standards of mercury species under gastrointestinal digestion conditions (72-98%). However their effectiveness is lower in food, and reductions in bioaccessibility are only observed with mushrooms (⩽68%). It is hypothesized that bioaccessible mercury in seafood forms part of complexes that do not interact with lactic acid bacteria.

BACKGROUND Metal sequestration by bacteria has been proposed as a strategy to counteract metal contamination in foodstuffs. Lactobacilli can interact with metals, although studies with important foodborne metals such as inorganic [Hg(II)] or organic (CH3Hg) mercury are lacking. Lactobacilli were evaluated for their potential to bind these contaminants and the nature of the interaction was assessed by the use of metal competitors, chemical and enzymatical treatments, and mutants affected in the cell wall structure. RESULTS Lactobacillus strains efficiently bound Hg(II) and CH3Hg. Mercury binding by Lactobacillus casei BL23 was independent of cell viability. In BL23, both forms of mercury were cell wall bound. Their interaction was not inhibited by cations and it was resistant to chelating agents and protein digestion. Lactobacillus casei mutants affected in genes involved in the modulation of the negative charge of the cell wall anionic polymer lipoteichoic acid showed increased mercury biosorption. In these mutants, mercury toxicity was enhanced compared to wild‐type bacteria. These data suggest that lipoteichoic acid itself or the physicochemical characteristics that it confers to the cell wall play a major role in mercury complexation. CONCLUSION This is the first example of the biosorption of Hg(II) and CH3Hg in lactobacilli and it represents a first step towards their possible use as agents for diminishing mercury bioaccessibility from food at the gastrointestinal tract. © 2017 Society of Chemical Industry

Mushrooms can accumulate toxic trace elements. The objectives of the present study are to evaluate levels of mercury, cadmium, lead, and arsenic in dried mushrooms, to determine the effect of cooking on the contents of these elements, and to evaluate their bioaccessibility in the mushrooms ready for consumption. The results showed that Hg levels in Amanita ponderosa, Boletus edulis, Marasmius oreades, and Tricholoma georgii, as well as Cd levels in some samples of Amanita caesarea and T. georgii, exceeded the legislated limits. Cooking significantly reduced the levels of As (26-72%), whereas the reduction in levels of Hg, Cd, and Pb was much lower. However, the bioaccessibility of As (63-81%) was higher than the values obtained for the metals (<40%). Taking the effects of cooking and gastrointestinal digestion into account gives a more realistic estimate of the risk associated with the consumption of mushrooms.

The synthesis of the inorganic polymer polyphosphate (poly-P) in bacteria has been linked to stress survival and to the capacity of some strains to sequester heavy metals. In addition, synthesis of poly-P by certain strains of probiotic lactobacilli has been evidenced as a probiotic mechanism due to the homeostatic properties of this compound at the intestinal epithelium. We analyzed the link between poly-P synthesis, stress response, and mercury toxicity/accumulation by comparing wild-type strains of Lactobacillus and their corresponding mutants devoid of poly-P synthesis capacity (defective in the poly-P kinase, ppk, gene). Results showed that resistance to salt (NaCl) and acidic (pH 4) stresses upon ppk mutation was affected in Lactobacillus casei, while no effect was observed in two different Lactobacillus plantarum strains. Inorganic [Hg(II)] and organic (CH3Hg) mercury toxicity was generally increased upon ppk mutation, but no influence was seen on the capacity to retain both mercurial forms by the bacteria. Notwithstanding, the culture supernatants of ppk-defective L. plantarum strains possessed a diminished capacity to induce HSP27 expression, a marker for cell protection, in cultured Caco-2 cells compared to wild-type strains. In summary, our results illustrate that the role of poly-P in stress tolerance can vary between strains and they reinforce the idea of probiotic-derived poly-P as a molecule that modulates host-signaling pathways. They also question the relevance of this polymer to the capacity to retain mercury of probiotics.

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Seafood products are important sources of proteins, polyunsaturated lipids and phospholipids, and also of numerous micronutrients (vitamins and minerals). However, they may also present chemical contaminants that can constitute a health risk and that must be considered when evaluating the risk/benefit associated with consumption of this group of foods. Toxic metals and metalloids in seafood, such as mercury (Hg), cadmium (Cd), arsenic (As), and lead (Pb), are subjected to legislative control in order to provide the consumer with safe seafood. This review provides an exhaustive survey of the occurrence of these toxic metal(loid)s in seafood products, and of the risk resulting from their consumption. Consideration is given to aspects related to speciation, food processing, and bioavailability, which are key factors in evaluating the risk associated with the presence of these toxic trace elements in seafood products.