Rudy Van Cauwenbergh

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

OBJECTIVEnInsoluble 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.nnnMETHODSnDairy 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.nnnRESULTSnCalcium 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%).nnnCONCLUSIONSnThis 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.

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.

Indication of silicon essentiality in humans: serum concentrations in Belgian children and adults, including pregnant women.

Serum silicon concentrations were determined in Belgian healthy children and adults, including pregnant women, by electrothermal atomic absorption spectrometry. Serum levels appeared to be significantly higher in healthy children (1–18 yr) than in healthy adults (19–60 yr). Especially, levels in infants (<1 yr) were higher than in any other group. Compared to age-matched nonpregnants, the serum silicon content was very low in pregnant women. In addition to the fact that this study for the first time provides serum silicon values in adults and children in Belgium, the most important observation is that these serum profiles might be an indication of silicon essentiality in man.

Dietary silicon intake in Belgium: sources, availability from foods, and human serum levels.

The dietary intake of silicon by using the duplicate portion sampling technique of 24 hour-meals during 7 consecutive days is estimated.Since plant-based foods are major sources of silicon the elemental content is determined in various vegetarian foodstuffs commercially available in Belgium.Mean silicon intake from the 24-hour duplicate meals consumed daily by nearly 2000 persons was 18.6 +/- 8.5 mg/day. The major food sources were unrefined grains of high fibre content, cereal products and root vegetables. For vegetarian foods rice and barley revealed high silicon levels. Very high serum concentrations in newborns and concomittant low levels in the mothers indicated a homeostatic mechanism in humans. Besides the dietary intake, serum silicon levels of various population groups support the concept of essentiality of the element. An in vitro dialysability of the element in a simulated digestion procedure is used as a surrogate of silicon uptake.Silicon was readily available from foods but this correlated inversely with the elemental content.Serum silicon levels, as a function of age, gave indication of an important role of this element. In vitro availability study proved an inverse relation with the elemental content. A preliminary in vivo experiment confirmed that bioavailability is not only determined by concentration, but especially by the type of food and species under which silicon is present.

A method for **in vitro** determination of calcium, iron and zinc availability from first-age infant formula and human milk

A method for in vitro determination of available calcium, iron and zinc content from infant food after digestion was evaluated. This method introduced an intraluminal digestive phase, adapted to the gastrointestinal conditions of infants younger than 6 months of age, prior to continuous flow dialysis of the resultant gastric digest. Precautions handling the method were discussed and enzymatic parameters were defined. Ruggedness of the method was determined from the availability of calcium, iron and zinc at different gastrointestinal conditions. Availability of all three elements was higher at gastric pH of 2 (20.0 +/- 1.1% for calcium, 4.06 +/- 0.66% for iron and 17.5 +/- 1.3% for zinc), than from the normal procedure (pH 4) (15.6 +/- 1.2% for calcium, 1.18 +/- 0.26% for iron and 8.2 +/- 0.9% for zinc). At pH 5, however, calcium availability appeared to be lower (11.7 +/- 1.0%) (P < 0.05). The intestinal pH also had a major influence on the availability. At low intestinal pH (5.5), availability was 40.5 +/- 2.3% for calcium, 3.01 +/- 0.58% for iron and 26.8 +/- 1.8% for zinc, which was higher compared with the normal procedure (P < 0.05). Moreover, other factors, such as digestion time, mixing and filtration pressure, also affected the availability. Recovery tests yielded mean values of 94 +/- 3% for calcium, 109 +/- 9% for iron and 106 +/- 4% for zinc. Mean intra- and inter-batch precision of the availability procedure was 4.1 CV% and 6.6 CV% for calcium, 14.5 CV% and 19.2 CV% for iron, and 4.0 CV% and 13.6 CV% for zinc. The method provides adequate accuracy, acceptable precision and good recovery. It offers the advantage of being simple, rapid and inexpensive, since it takes only 1 day to run the whole availability procedure (including four replicates per sample), and the low costs of the dialysis equipment. It can therefore be considered as suitable for predicting the availability of essential elements from foods used during the first months of infancy.

Spectrometric determination of silicon in food and biological samples: an interlaboratory trial

Accuracy and precision of silicon determination in biological matrices (serum, urine, water, beer and spinach) by spectrometric techniques (when necessary after acid destruction) were assessed by means of a collaborative interlaboratory trial. The trial was set up in accordance with ISO 5725-2 (1994). The relative overall repeatability standard deviation was acceptable. It varied between 4% for spinach powder (mean content: 176xa0mgxa0kg−1) and 11% for serum (mean content: 5.33xa0mgxa0L−1). On the other hand, the relative overall between-laboratory standard deviation was found to vary from a satisfactorily 15% for spinach after destruction (mean content: 3.32xa0mgxa0L−1) to an unacceptable 107% for spinach powder (mean content: 176xa0mgxa0kg−1). The overall conclusion of the trial was that silicon determination in biological matrices can properly be performed by spectrometric techniques. However, when sample pretreatment (i.e., acid destruction) is needed prior to silicon determination problems still remain.

Daily dietary chromium intake in Belgium, using duplicate portion sampling

Daily dietary chromium intake in Belgium has been evaluated by sampling duplicate portions of food, heating them at an acidic pH in a microwave oven and then quantifying the chromium by atomic absorption spectrometry. The mean intake value (53±31 μg/day) is similar to levels found for most other countries and is situated at the lower end of the recommended range for a safe and adequate daily dietary intake.

Measurement of the daily dietary calcium and magnesium intake in Belgium, using duplicate portion sampling.

The daily dietary calcium and magnesium intakes in Belgium were evaluated by sampling duplicate portions of food, destruction in a microwave oven and their calcium and magnesium contents determined by atomic absorption spectroscopy. The mean intake value for calcium (618±125 mg/day) was found to be less than those values measured in most other countries and was below the recommended daily allowance (RDA). The mean intake value for magnesium (271±44 mg/day) was similar to levels found in most other countries, but was below the RDA value for healthy adult men (350 mg/day) whilst being adequate for healthy women (280 mg/day).

Daily dietary manganese intake in Belgium, using duplicate portion sampling.

ZusammenfassungDie tägliche Aufnahme von Mangan mit der Nahrung in Belgien wurde durch doppelte Probenahme von Portionen, Aufschluß derselben im Mikrowellen-Ofen und Atomapsorptionsspektrophotometrie bestimmt. Die mittlere Aufnahme lag bei 3.1±1.1 mg je Tag. Das entspricht Werten, wie sie in anderen Ländern gefunden wurden und liegt in den von WHO/RDA und NRC, USA empfohlenen Bereichen.AbstractDaily dietary manganese intake in Belgium was evaluated by duplicate portion sampling, destruction by cooking in a microwave oven and subsequent analysis for this element by atomic absorption spectrometry. The mean intake value (3.1±1.1 mg/day) is similar to levels found for most other countries and is within WHO/RDA and National Research Council, USA recommended intake ranges.

Silicon in Foods: Content and Bioavailability

The silicon content of various foodstuffs marketed in Belgium was measured by a validated graphite furnace absorption spectrometric method. Dietary intake has been identified as the major source of silicon. However, data on its bioavailability remain scarce and insufficient. In vitro methods can provide an indication of bioavailability in case of lacking in vivo data. Bioavailability of silicon from different foodstuffs was estimated using an in vitro continuous flow gastroduodenal simulation method. The major food sources of silicon were unrefined grains, cereal products and root vegetables. The availabilities of silicon from, meat, milk and beers were high, whereas low availability was observed for seafood and cereal products. Plotting the availability data versus the total elemental silicon content of the foods revealed an exponential inverse relationship. The inverse relationship between silicon content and silicon availability was found in all foods, with the exception of various silicon containing drinks. Nevertheless, food categories classified as major silicon sources in the diet still appear to provide the highest absolute amounts of available silicon per 100 g of food including breakfast cereals, bread and baking products, and beers.