H. Deelstra

Interlaboratory trial on the determination of the In Vitro iron dialysability from food

An in vitro method for the estimation of iron bioavailability was subjected to an interlaboratory trial. The method involved a simulated gastrointestinal digestion using pepsin for the gastric stage followed by pancreatin and bile salts for the intestinal stage. The proportion of iron diffused through a semipermeable membrane (molecular mass cut-off 10 kDa) was used to measure the iron dialysability. An interlaboratory trial between nine laboratories was conducted to evaluate the repeatability and reproducibility of the agreed method. The reproducibility of the method among the participating laboratories was 20-30% and depended on the content of dialysable iron. Several factors contributing to the variation in the in vitro dialysability among laboratories are discussed. The pH adjustment in the intestinal digestion was identified as one of the critical parameters. The present in vitro method was used to evaluate the iron dialysability from three meals. The dialysability data were in reasonable agreement with human absorption data. The usefulness of the in vitro dialysability method is discussed.

Availabilities of calcium, iron, and zinc from dairy infant formulas is affected by soluble dietary fibers and modified starch fractions.

OBJECTIVE Insoluble dietary fiber is a known inhibitor of mineral absorption, whereas the effects of soluble dietary fibers (including prebiotics) are less known. The aim was to study calcium, iron, and zinc availabilities from dairy infant formulas supplemented with soluble dietary fibers and modified starches in vitro. METHODS Dairy infant formulas were supplemented with soluble dietary fibers (3%, dry wt) and modified starches (16% pregelatinized rice starch and 1.9% maltodextrin, dry wt) and kept in a well-controlled and defined environment in vitro. Pooled mature human milk was used as the reference standard. RESULTS Calcium availability from standard formula was elevated by 30% after inulin supplementation (17.2%), whereas locust bean gum (11.9%) and high esterified pectin (11.7%) reduced availability by approximately 10%. Iron availability from standard formula was increased by pregelatinized rice starch (3.8%), whereas availability was reduced in the following order: high esterified pectin (2.3%), oligofructose (2.2%), and low esterified pectin (2.1%). Zinc availability was highest after the addition of pregelatinized rice starch (13.5%) but lowest with the addition of locust bean gum (6.8%) and maltodextrin (5.4%). CONCLUSIONS This study showed that addition of soluble dietary fiber affects calcium, iron, and zinc availabilities in positive (inulin) and negative ways, depending on the type of the dietary fiber used.

Effect of thickening agents, based on soluble dietary fiber, on the availability of calcium, iron, and zinc from infant formulas.

Although it is accepted that dietary fiber probably is not needed in the diets of infants younger than 1 y, babies suffering from regurgitation are often fed with infant formulas thickened with considerable amounts of fiber. The effect of increasing amounts of alginic acid, locust-bean gum, and guar gum was studied from casein and whey-based infant formulas. A dialysis in vitro method with preliminary intraluminal digestion, adapted to the conditions of infants younger than 6 mo, was used. Human milk was used as the reference standard. Elemental contents of samples and dialysates were determined by atomic absorption spectrometry. Soluble dietary fiber inhibited mineral availability more in casein than in whey-based formulas. Mineral availabilities from casein- and whey-based formulas supplemented with 0.42 g of locust-bean gum/100 mL were 9.4% (0.7) and 10.4% (0.6) for calcium (P < 0.05), 0.32% (0.08) and 1.45% (0.17) for iron (P < 0.05), and 3.2% (0.2) and 5.6% (0.5) for zinc (P < 0.05), respectively. Calcium availability from the whey formula decreased in the presence of each fiber source, especially guar gum and alginic acid. Supplementing 2 g of alginic acid-based agents per 100 mL depressed calcium availability from 13.3% (1.2) to 5.3% (0.3; P < 0.05). With respect to iron and zinc, availabilities increased from 1.28% (0.28) to 6.05% (0.96; P < 0.05) and from 6.7% (0.6) to 10.2% (1.0), respectively, with the addition of 2 g of alginic acid (P < 0.05). Both gums lowered iron and zinc availabilities, and guar gum affected iron availability more severely than locust-bean gum did. Iron availabilities were 1.45% (0.17) from formula thickened with locust-bean gum (0.42 g/100 mL) and 0.92% (0.15) from formula thickened with guar gum (P < 0.05). Adding thickening agents based on soluble dietary fiber to traditional infant formulas probably affects calcium, iron, and zinc availability in various ways.

Selenium in human urine determination, speciation and concentration levels.

Procedures for determination of selenium in urine samples are reviewed. Basic problems encountered in sampling and sample-treatment are discussed. Concentration levels and spedation of the element are summarized.

Copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in fish from Lake Tanganyika, Burundi

Atomic absorption spectrometric determination of copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in two fish species from Lake Tanganyika, Burundi, provide values that are lower than most literature data, especially for cadmium, arsenic and mercury. Tissue analysis of Lates stapersii reveals that liver accumulates the highest amount of most elements. The data illustrates that Lake Tanganyika is still a non-polluted area at the time of analysis.

Modification of an in-vitro method for estimating the bioavailability of zinc and calcium from foods

ZusammenfassungEine continuous-flow-Methode zur in-vitro-Bestimmung der Bioverfügbarkeit von Mineralien und Spurenelementen wurde verbessert. Die Proben werden mit Pepsin in einer Dialysezelle verdaut, der pH-Wert dabei graduell verändert und bei der nachfolgenden Verdauung mit Pankreas-Galle-Extrakt die freigesetzten Mineralstoffe kontinuierlich durch Dialyse abgezogen. Der dialysierbare Anteil gilt als Maß für die Bioverfügbarkeit. Ein Vergleich der so erhaltenen Daten für Zink und Calcium aus Milch- und Soja-Formulanahrung zeigt gute Übereinstimmung mit in-vivo-Messungen. Die Methode dürfte sich zur Vorhersage der Bioverfügbarkeit für Mineralstoffe eignen.AbstractA continuous flow in-vitro method for estimating the bioavailability of minerals and trace elements was modified. This modified method includes a simulated gastric digestion with pepsin, gradual pH change during the first 30 min of dialysis in an Amicon stirred cell, and a further 2 h of continuous dialysis accompanied by intestinal digestion with pancreatin-bile extract. The percentage of continuously dialysed minerals or trace elements (dialysability) is used to express the bioavailability. Comparison of different in-vitro methods by using the dialysability of zinc and calcium from milk- and soy-based formula samples revealed that with the modified method the results are closer to the in-vivo situation and could be used as a relative index for predicting the bioavailability of some minerals and trace elements.

Thickening infant formula with digestible and indigestible carbohydrate: availability of calcium, iron, and zinc in vitro.

BACKGROUND Regurgitation is common in infants and is usually due to gastroesophageal reflux. Often parental reassurance and dietary management by feeding thickened formulas are the only therapeutic steps necessary. Adding fibers may interfere with the absorption of micronutrients. METHODS A continuous-flow dialysis in vitro method with a preliminary intraluminal digestive phase, modified to simulate the conditions of infants less than 6 months of age and children from 6 months of age on, was used to study the availability of calcium, iron, and zinc from thickened and nonthickened first-and second-age infant formulas. Pooled mature human milk was used as the reference standard. The elemental content of the samples and dialysate fractions of calcium, iron, and zinc after digestion was determined by atomic absorption spectrometry. RESULTS In human milk, calcium, iron, and zinc were highly available for absorptive processes. Availability of calcium, iron, and zinc from nonthickened first- and second-age infant formulas tends to be significantly better than in the corresponding products thickened with locust bean gum. Thickening infant formulas with pregelatinized rice starch, however, does not affect the availability of calcium, iron, and zinc. CONCLUSIONS It appears that human milk provides optimal conditions for the availability of calcium, iron, and zinc. Availability of calcium, iron, and zinc seems to lower when infant formulas are thickened with indigestible carbohydrates, whereas it does not by adding digestible carbohydrates.

Daily dietary intake of copper, zinc and selenium by different population groups in Burundi, Africa

Daily dietary intake of copper, zinc and selenium for different population groups in Burundi, Africa, has been determined, using different sampling strategies, by atomic absorption spectrometry. Recommended daily intakes (RDA, National Academy, USA) are met for copper and zinc. For selenium, especially the rural population risk a deficiency as observed with a daily intake of 17 micrograms. The importance of different types of food in daily intake is discussed. Legumes proved to be an important source of copper, while for selenium fish contributes in a large part in dietary intake. Calculated total daily intakes are compared with intakes recently published for other countries.

In vitro availability of calcium, iron, and zinc from first-age infant formulae and human milk.

Background Variation in the bioavailability of calcium (Ca), iron (Fe), and zinc (Zn) occurs because of interactions of food components in the gastrointestinal microenvironment. Bioavailability is preferably determined by in vivo tests, but these are expensive, labor-intensive, time consuming, and often unethical. As an alternative, in vitro methods can be used to predict bioavailability of nutrients from foodstuffs. Methods A continuous-flow dialysis model with preliminary intraluminal digestive phase, adapted to the gastrointestinal conditions of infants younger than 6 months, was used. Human milk was the reference standard. Ca, Fe, and Zn content of samples and dialysates after digestion were analyzed by atomic absorption spectrometry. Results Ca availability is similar in human milk (13.1% ± 0.8%), whey (13.3% ± 1.2%), and soy-based formulae (13.0% ± 1.2%;P > 0.05), and higher in casein-predominant formula (21.2% ± 0.6%;P < 0.05). Availability of Fe is highest in human milk (8.12% ± 0.27%;P < 0.05). Fe availability in whey (1.28% ± 0.28%) and soy formulae (1.48% ± 0.28%) is similar (P > 0.05), but availability is lower in casein-predominant formula (0.48% ± 0.22%;P < 0.05). Zn availability is also highest in human milk (13.1% ± 0.7%;P < 0.05). However, Zn availability is similar in whey (6.7% ± 0.6%) and casein formulae (8.5% ± 1.6%;P > 0.05), but lower in soy formula (2.3% ± 0.4%;P < 0.05). Conclusions Our observations are in agreement with previous data from in vivo studies in term infants. This in vitro procedure is an inexpensive, simple, rapid, and reliable method that predicts the bioavailability of Ca, Fe, and Zn in foods.

Estimation of the bioavailability of zinc and calcium from human, cow's, goat, and sheep milk by an in vitro method.

The availability of zinc and calcium from human, cows, goat, and sheep milk is evaluated by an in vitro method that involves a simulated human gastrointestinal digestion followed by measurement of dialyzability of zinc and calcium. Zinc availability of milk showed the highest value for human milk (15.0%) and the lowest for sheep milk (1.0%), in both whole and skim milk. Calcium availability of the different types of milk did not differ significantly and ranged between 18 and 23%. No significant differences in availability between whole and skim milk were found for both elements, except for zinc in cows milk.