Hydrothermal treatment and malting of barley improved zinc absorption but not calcium absorption in humans.

OBJECTIVE: To study whether hydrothermal treatment or malting of barley (cv. Blenheim) improves zinc and calcium absorption in humans. DESIGN: : Two groups of 10 and 12 healthy subjects, respectively, were in a period of 2 months in a fasting state, served two single meals each containing porridge or breakfast cereals prepared from processed or unprocessed (control) barley (60 g). The meals included 200 g of milk, extrinsically labelled with (65)Zn and (47)Ca. Whole-body retention of both minerals was measured. SETTING: The study was carried out at the Department of Radiation Physics, Sahlgrenska University Hospital, Göteborg. SUBJECTS: The subjects were recruited among students at the Göteborg University. None dropped out. INTERVENTIONS: The activities of (65)Zn and (47)Ca were measured by whole-body counting four to five times over a 4-week period after each meal. RESULTS: Zinc absorption from hydrothermally treated barley porridge, containing 28 mg P as inositol tri- to hexaphosphates (InsP(3)-InsP(6)), was significantly higher (P<0.001) than from control porridge containing 111 mg P as InsP(3)-InsP(6), 25.2+/-6.9 vs 11.0+/-2.5% (n=12). Calcium absorption did not differ (P>0.05), 21.1+/-6.8 vs 19.5+/-4.7% (n=12). Zinc absorption from breakfast cereals of malted barley with phytase activity and containing 70 mg P as InsP(3)-InsP(6,) was significantly higher (P<0.05) than from flakes of barley, containing 108 mg P as InsP(3)- InsP(6) and no phytase activity, 22.9+/-5.8 vs 14.8+/-4.6% (n=10). The calcium absorption was 21.3+/-6.5 vs 18.5+/-4.3% (n=10) and did not differ significantly (P>0.05). CONCLUSION: Improvements of zinc absorption in breakfast meals can be achieved by optimised hydrothermal treatment or malting of barley. Calcium absorption was not influenced in the meals in this study. SPONSORSHIP: Supported by Semper AB, Sweden, Oy Lahden Polttimo, Finland, the SL-Foundation, Sweden, Swedish National Board for Industrial and Technical Development (NUTEK), the Nordic Industrial Foundation, Swedish Council for Forestry and Agricultural Research (SJFR, project no 50.0306/97).

Determination of the retention of 47Ca by whole-body counting.

Retention of intravenously or orally administered 47Ca in the human body are described by a two-parameter function. It is then sufficient to make only a few whole-body measurements to determine the retention function, avoiding faeces sampling and stool markers. Seven days after intake the non-absorbed calcium was excreted and the model agreed with the measured relative retention. Absorption of calcium could then, in some cases (e.g. comparative studies), be described by relative retention at the 7th day after intake.

Sodium iron EDTA [NaFe(III)EDTA] as a food fortificant does not influence absorption and urinary excretion of manganese in healthy adults.

NaFe(III)EDTA is a promising iron (Fe) compound for food fortification programs because of its high Fe bioavailability from meals containing dietary inhibitors of Fe absorption such as phytic acid. However, this Fe compound is not currently used in any large-scale fortification program because of concern over its possible negative influence on the metabolism of other essential minerals or its possible influence on the absorption of potentially toxic elements, such as manganese (Mn). In this study, Mn absorption and urinary excretion were studied in adults after intake of an Fe-fortified weaning cereal labeled with 54Mn. In a crossover design, the fortification of the weaning cereal with Fe as NaFeEDTA was compared with ferrous sulfate. Manganese absorption was measured by extrapolation from whole-body retention data 10-30 d after intake, and urinary excretion of 54Mn was measured over 7 d. No significant differences in 54Mn absorption or urinary excretion were found; 1.1 +/- 0.15 and 0.91 +/- 0.35% of the ingested dose was absorbed from the cereal fortified with NaFe(III)EDTA and FeSO4, respectively. Urinary excretion of 54Mn was very low; the total radioactivity in urine represented 1.1 +/- 0.55% of the absorbed dose with NaFe(III)EDTA and 0.72 +/- 0.53% of the absorbed dose with FeSO4. Until now, Fe-fortification programs have met with only limited success. The introduction of NaFeEDTA as a food fortificant could be a useful tool to provide bioavailable Fe to vulnerable groups in the population and thus aid in combating Fe deficiency.

Zinc absorption in adult humans: the effect of protein sources added to liquid test meals.

The influence of different protein sources on Zn absorption was evaluated in healthy adults by radioisotopic labelling of single meals, followed by whole-body retention measurements 14 d after intake. Semi-synthetic liquid diets were used for the evaluation of different animal-protein sources and dephytinized soyabean-protein isolate (< 0.01 g phytic acid/kg). Zn absorption was measured in the same subjects from identical test meals containing no added protein. No statistically significant differences were found in the Zn absorption from test meals containing bovine whey, casein or egg albumen when compared with test meals without added protein. Bovine serum albumin (BSA) and soyabean-protein isolate (< 0.01 g phytic acid/kg) significantly reduced the mean absorption of Zn from 45-49% (no added protein) to 38.0 (SD 10.9) (BSA, P < 0.05) and 33.9 (SD 12.6)% (soyabean-protein isolate < 0.01 g phytic acid/kg, P < 0.01). These results demonstrate that Zn absorption is inhibited by certain protein sources, such as BSA and dephytinized soyabean-protein isolate, while other proteins have little or no effect.

Manganese absorption in humans: the effect of phytic acid and ascorbic acid in soy formula.

The absorption of manganese from soy formula was studied in adult volunteers by extrinsic labeling of test meals with 54Mn, followed by whole-body retention measurements for approximately 30 d after intake. Eight subjects participated twice in each of the two studies, acting as his or her own control. Soy formula containing the native content of phytic acid was compared with a similar dephytinized formula: geometric mean manganese absorption increased 2.3-fold from 0.7% (range: 0.2-1.1%) to 1.6% (range: 1.0-7.2%) (P < 0.01) with the dephytinized formula. In addition, the effect of the ascorbic acid content of the phytic acid-containing formula was investigated. Manganese absorption was not influenced by an increase in the ascorbic acid from 625 mumol/L (110 mg/L) to 1250 mumol/L (220 mg/L): the geometric mean manganese absorption was 0.6% (range: 0.3-1.0%) and 0.6% (range: 0.3-1.1%), respectively. In conclusion, fractional manganese absorption was approximately doubled by the dephytinization of soy formula but was not influenced by an increase in the ascorbic acid content of a soy formula containing the native amount of phytic acid.

Zinc absorption in adult humans: the effect of iron fortification.

The effect of Fe fortification on the absorption of Zn was studied by radioisotopic labelling of single meals, followed by measurements of whole-body retention of 65Zn at 14 d after intake. Healthy adult volunteers participated in the study. Weaning cereal, wheat bread and infant formula, foods that are all frequently Fe-fortified, were evaluated in the study. The amounts of Fe added as FeSO4 were similar to the levels in commercial products in Europe and the USA, and were 200 or 500 mg Fe/kg (weaning cereal), 65 mg Fe/kg (white wheat flour) and 12 mg Fe/l (infant formula). For comparison, Zn absorption was measured in the same subjects, from identical test meals containing no added Fe. No statistically significant differences were found when Zn absorption from the Fe-fortified test meals was compared with that from non-Fe-fortified test meals. Fractional Zn-absorption values from Fe-fortified v. non-fortified meals were 31.1 (SD 11.9) v. 30.7 (SD 7.0)% (weaning cereal; 200 mg Fe/kg), 37.7 (SD 16.6) v. 30.2 (SD 9.9)% (weaning cereal; 500 mg Fe/kg), 36.5 (SD 14.4) v. 38.2 (SD 18.1)% (bread; 65 mg Fe/kg flour) and 41.6 (SD 8.1) v. 38.9 (SD 14.5)% (infant formula; 12 mg Fe/l). The addition of Fe to foods at the currently used fortification levels was thus not associated with impaired absorption of Zn and the consumption of these Fe-fortified foods would not be expected to have a negative effect on Zn nutrition.

Effect of protein level and protein source on zinc absorption in humans.

The effect of increasing levels of various protein sources on zinc absorption from a legume-based meal was studied in humans with the use of a radionuclide technique. The meals were extrinsically labelled with 65Zn and absorption was determined from measurements of the whole-body retention of the isotope. The mean fractional zinc absorption for the 13 meals was 24.7 +/- 6.9% and was only influenced by the protein content of the meal to a limited extent (r = 0.45). However, the amount of zinc absorbed from the meals was strongly correlated with both the protein (r = 0.85) and zinc content (r = 0.86): 5.9 +/- 1.7 mumol of zinc was absorbed from the basal bean meal which had the lowest protein content; the addition of low zinc chicken doubled the protein content and increased zinc absorption to 10.3 +/- 2.0 mumol; the addition of zinc-rich beef also doubled the protein content, however, zinc absorption was increased to 15.9 +/- 4.7 mumol. It is concluded that the zinc content of the main protein source of the diet determines the amount of zinc absorbed to a large extent. However, relatively small amounts of animal protein can significantly improve the value of a legume-based meal as a source of zinc.

Zinc absorption in humans from meals based on rye, barley, oatmeal, triticale and whole wheat.

The absorption of zinc from meals based on 60 g of rye, barley, oatmeal, triticale or whole wheat was studied by use of extrinsic labelling with 65Zn and measurement of the whole-body retention of the radionuclide. The cereals were prepared in the form of bread or porridge and were served with 200 mL of milk. The oatmeal flakes were also served without further preparation. The absorption of zinc was negatively correlated to the phytic acid content of the meal with the highest absorption, 26.8 +/- 7.4%, from the rye bread meal containing 100 mumol of phytic acid and the lowest, 8.4 +/- 1.0%, from oatmeal porridge with a phytic acid content of 600 mumol. It is concluded that food preparation that decreases the phytic acid content improves zinc absorption.