Analysis of total and dialyzable copper levels in duplicate meals by ETAAS: daily intake

In situ analysis of copper speciation during in vitro digestion: Differences between copper in drinking water and food

In recent years, the safety of copper in drinking water has increasingly been questioned. Copper speciation is an important factor that affects its bioavailability and toxicity; thus, it is critical to investigate the speciation of copper that is ingested from food and drinking water during in vitro digestion. After digestion, water- and food-derived copper formed 60 ± 4% 0.1-1 kDa and 49 ± 6% 10-1,000 kDa copper complexes, respectively. Under simulated fasting drinking water conditions, up to 90 ± 2% 0.1-1 kDa copper complexes formed. In addition, using ion selective electrode analysis, water-derived copper was detected that contained higher Cu²⁺ concentrations after digestion than those of food-derived copper. These results indicate that water-derived copper forms smaller-sized species and exhibits higher Cu²⁺ concentrations during digestion than those of food-derived copper, thereby highlighting the importance of reassessing the safety limit for copper in drinking water.

The influence of gastrointestinal pH on speciation of copper in simulated digestive juice

Speciation can provide knowledge about absorption, reactivity to binding sites, bioavailability, toxicity, and excretion of elements. In this study, the speciation of copper in different model solutions under the influence of gastrointestinal (GI) pH was studied by ion selective electrode (ISE) and inductively coupled plasma optical emission spectrometry (ICP OES). It was found that the electrode response (mV) against Cu2+ decreased with the increase in pH and dropped to the lowest point at pH 7.5 in all model solutions. When amino acids and organic acids were present, the ratio of filtered copper (0.45 μm, pH 7.5) was more than 90%. When casein was present, whey protein, pancreatin, and starch were added, and the ratio of filtered copper was 85.6 ± 0.3, 56.7 ± 8.8, 38.5 ± 5.1, and 1.0 ± 0.3%, respectively. When there is not enough organic ligand, excessive copper will form copper hydroxide precipitation with the increase in pH, but it got the highest electrode response (mV) against Cu2+. From this study, it can be concluded that the speciation of copper in GI tract is strongly influenced by the pH and the composition of food. When there are few ligands coexisting in the GI tract, the concentration of copper ion may be relatively high.

Correlating enzyme density, conformation and activity on nanoparticle surfaces in highly functional bio-nanocomposites

The biological activity of the immobilized enzyme is crucial for the performance of different nanoparticle mediated enzymatic assays, where enzymatic conversion can be used for label-free analyte detection. In this article we have addressed two significant aspects of enzyme-nanoparticle interactions. First, we have developed copper sulfide (CuS) nanoparticles with an average diameter of 25 nm as a potential enzyme-interface using trypsin protease as a model enzyme. CuS nanoparticles showed high trypsin immobilization capacity of about 14.0 mg m(-2) with the significant retention of native enzymatic activity (75-98%) at room temperature, even beyond the calculated tightly packed monolayer coverage (which is around 4.1 mg m(-2)). Second, we report a quantitative correlation between the structure-functional relationship and the density of immobilized trypsin on a nanoparticle surface. The in situ conformation of immobilized trypsin could be efficiently analyzed by fluorescence, circular dichroism and FT-IR spectroscopic measurements because of the small size of the nanoparticles. Trypsin molecules appear to retain their close-native tertiary and secondary structural features (with a small loss of 1-2% of helical content) in the entire surface density range (2.0-14.0 mg m(-2)) on the CuS nanoparticles. However, interestingly, at a low surface coverage (2.0 mg m(-2)), immobilized trypsin retains almost 98% of its native enzymatic activity, leading to a highly functional bio-nanocomposite. However, at higher surface coverages, the enzyme activity decreases to 77%, indicating the influence of steric crowding. Furthermore, the high functionality of the immobilized trypsin at low surface density on CuS nanoparticle was also confirmed by determining the kinetic parameters of enzymatic activity.

Daily dietary intakes of zinc, copper, lead, and cadmium as determined by duplicate portion sampling combined with either instrumental analysis or the use of food composition tables, Shiraz, Iran

Estimation of essential and toxic element intakes is crucial to evaluate the risks of deficiency or toxicity. The purpose of this study was to investigate and also to compare the dietary intakes of zinc (Zn) and copper (Cu) by adults living in Shiraz, Iran, determined by two procedures: duplicate portion sampling of 21 hospital meals combined with either instrumental analysis (voltammetric measurement) or the use of food composition tables (FCTs). The level of exposure to lead (Pb) and cadmium (Cd) was evaluated as well. The daily Zn intakes of both methods were not significantly different and were higher than the RDA values except the value measured by the instrumental analysis which was lower than the RDA established for a male adult. Daily intake of Cu determined by instrumental analysis was significantly lower and closer to RDA for adults compared with the value estimated by FCTs. The dietary intakes of Pb and Cd were 313 and 61% of the respective provisional tolerable weekly intakes (PTWIs), respectively. The accuracy of two methods used for estimation of Zn intake was similar. In the case of Cu, the use of FCTs, in which the influence of environmental conditions and dietary habits of meal preparation is not taken into account, overestimated dietary intake. The risk of zinc deficiency was found in adult males. Moreover, the estimated intake of Pb, but not Cd, could be a cause of concern for Shiraz population. Thus, conducting regular periodic studies to assess the dietary intake of mentioned elements are recommended.

Dialysability of magnesium and calcium from hospital duplicate meals: influence exerted by other elements

Total and dialysable magnesium and calcium levels and corresponding dialysabilities were measured in duplicate meals (n = 108) during 36 consecutive days. The interaction exerted by other nutrients and energy on them was also performed. Total mean magnesium and calcium fractions of 113.9 +/- 98.3 and 337.2 +/- 278.9 mg/meal respectively, were found. The Mg and Ca levels supplied by meals are positively (p < 0.05) correlated with macronutrient contents (carbohydrates and proteins). The mean dialysable Mg and Ca fractions were 56.9 +/- 36.3 and 127.4 +/- 112.3 mg/meal (50.4 +/- 13.2 and 37.8 +/- 10.7% as dialysabilities, respectively). Total Mg and Ca levels are significantly correlated with corresponding element dialysabilities (p < 0.05). For both minerals, significant correlations between their total and dialysable fractions and between their dialysable level and dialysabilities were noted (p < 0.01). The mean Mg and Ca daily dietary intakes (DDI) were 341.7 +/- 68.0 and 1,011.6 +/- 424.4 mg/day, respectively. For Ca and Mg the existence of similarities in their behaviour in meals and absorptive processes has been found. Duplicate meals with raw vegetables are good sources of bioaccessible Mg. High Ca dialysability has been found in the analysed meals. The fish and products constitute a good source of bioaccessible Ca. Mg, Ca, zinc, and chromium levels enhanced significantly the Mg dialysability. The Ca dialysability rose significantly with dialysable Ca and chromium fractions (p < 0.05).

Iron dialyzability from hospital duplicate meals: daily intake

Both total and dialyzable iron levels and corresponding dialyzability were determined in 108 duplicate meals during 36 consecutive days. Total mean iron fraction of 5.90 +/- 4.97 mg was found in the meals. The iron supplied by the meals is directly and significantly (p < 0.05) correlated with macromicronutrient content (carbohydrates, fiber, and protein). The mean iron dialyzability (4.81 +/- 3.25%) was low and not significantly different among the three primary meals (breakfast, lunch, and dinner). Significant interactions of several minerals on iron levels were found (p < 0.05). Iron dialyzability was only statistically influenced by zinc dialyzability in meals (p < 0.05). The dialyzed iron fraction present in meals was significantly correlated with protein and ascorbic acid levels (p < 0.01). The mean iron daily dietary intake was 17.7 +/- 6.91 mg. The hospital meals provided enough iron. Foods of animal origin are primary sources of iron in diet.