Copper absorption from human milk, cow's milk, and infant formulas using a suckling rat model

Since copper deficiency is known to occur during infancy, it becomes important to assess copper uptake from various infant diets. We have investigated the uptake of copper from human milk, cow's milk, cow's milk formulas, cereal/milk formula and soy formula, compensating for the decay of 64Cu and using the suckling rat as a model. Radiocopper was added to the diet in trace amounts. Ultracentrifugation, ultrafiltration, and gel filtration were used to show that the added 64Cu bound to milk fractions and individual binding compounds in a manner analogous to the distribution of native copper, thus validating the use of extrinsically labeled diets. Labeled diets were intubated into 14-day-old suckling rats. Animals were killed after 6 h and tissues removed and counted. Liver copper uptake was 25% from human milk, 23% from cow's milk formula, 18% from cow's milk, 17% from premature (cow's milk based) infant formula, 17% from cereal/milk formula and 10% from soy formula. These results show that the rat pup model may provide a rapid, inexpensive, and sensitive method to assay bioavailability of copper from infant foods.     

Relative zinc availability in human breast milk, infant formulas, and cow's milk

The concentration and bioavailability of zinc was analyzed in 10 varieties of milk. The concentration of zinc averaged 4.1 microgram/ml in unprocessed (raw) cow's milk; fortified infant formulas contained about 3 to 5 microgram Zn/ml; human breast milk and processed cow's milk contained approximately 2 microgram Zn/ml; sweetened condensed milk contained 1.3 microgram Zn/ml, and reconstituted nonfat dry milk contained 0.4 microgram Zn/ml. The mean values for zinc bioavailability to rats were as follows: sweetened condensed milk = 66%; human breast milk 59.2%, processed cow's milk = 43.7 to 50.9%; unprocessed (raw) cow's milk = 42%; nonfat dry milk = 41.2%, and infant formulas = 26.8 to 39.5%. Assuming similar absorption of zinc in rats and humans, our experimental results provide some guidelines for estimating the quantity of zinc that would actually be absorbed from various types of milk.     

In vitro determination of calcium bioavailability of milk, dairy products and infant formulas

In this study, the aim was to determine the in vitro calcium bioavailability of different dairy products and to investigate the effect of dry matter, fat, acidity and calcium content on calcium bioavailability of the products. For this purpose, the dry matter, fat, acidity and calcium content of different kinds of milk, yogurt, cheese and infant formulas were analysed. Then, calcium bioavailability of products was determined by an in vitro method that involves simulating gastrointestinal digestion of the product with pepsin-HCl and pancreatin-biliary salts, and then measuring the fraction of element that dialyses through a membrane of a certain pore size. Each of the product groups was examined statistically and no difference was found among milk, yogurt and infant formula groups in terms of calcium bioavailability. However, there were differences among cheese kinds according to the results of the Duncan test; all cheese kinds were considerably different from each other (P < 0.05). Moreover, it was found that calcium, dry matter, fat content and acidity did not affect the calcium bioavailability (P < 0.05). According to the results of statistical analysis that was applied to all product groups, it was found that the yogurt group was different from the other products and that the acidity affected calcium bioavailability (P < 0.05).     

Intrinsic and extrinsic stable isotopic zinc absorption by infants from formulas

The kinetics of fecal elimination and the extent of fractional absorption of intrinsic and extrinsic zinc from infant formula were studied in 11 human infants by using a direct, simultaneous dual-label method based on fecal monitoring of unabsorbed stable isotope labels. The relative positions of the two stable isotopic tags (67Zn, 70Zn) as extrinsic and intrinsic labels were reversed in two separate determinations of fractional absorption. Administration of doubly labeled formula for 24 h or less permitted elimination of unabsorbed labels before the end of a 72-h metabolic interval. The extent of enrichment and the kinetics of fecal elimination of unabsorbed extrinsic stable isotopic zinc tag were observed to agree closely with the corresponding values for the intrinsic tag. Fractional absorption of intrinsic and extrinsic tags was highly correlated and did not differ significantly. The ratio of fractional absorption of extrinsic tag to that of intrinsic tag was 1.05 +/- 0.19 (mean +/- SD). The results constitute strong support for validation of the use of enriched stable isotopes at low levels (less than or equal to 10%) of extrinsic addition to milk-based diets for studies of zinc absorption by humans.     

Calcium and zinc absorption from lactose-containing and lactose-free infant formulas

BACKGROUND: Calcium absorption is enhanced by the presence of lactose, but the quantitative significance of this effect in infant formulas is uncertain. It is also not known whether lactose affects zinc absorption. OBJECTIVE: We measured the absorption of calcium and zinc from infant formulas by using a multitracer, stable-isotope technique. DESIGN: Eighteen full-term infants (aged 8-12 wk at enrollment) were fed 2 partially hydrolyzed whey-protein-based formulas ad libitum for 2 wk per formula. The carbohydrate source was lactose in one formula and glucose polymers in the other (lactose-free). Infants were studied in a blinded crossover fashion after 2 wk of adaptation to each formula. Isotope absorption studies were conducted with a 4-tracer method in which (70)Zn and (44)Ca were provided orally and (67)Zn and (46)Ca intravenously. Zinc and calcium absorption was measured from the fractional excretion of the oral and intravenous isotopes in urine. RESULTS: Fractional and total calcium absorption was significantly greater from the lactose-containing formula than from the lactose-free formula. For total calcium absorption, the mean difference between formulas was 10.3% (P = 0.002) and 60 mg/d (P = 0.006). For zinc, fractional absorption (32 +/- 11%), total absorption, and intake did not differ significantly between the 2 formulas. CONCLUSIONS: The presence of lactose in a formula based on cow-milk protein increases absorption of calcium but not of zinc. Absorption of calcium from a lactose-free infant formula is, however, adequate to meet the calcium needs of full-term infants when the formula's calcium content is similar to that of lactose-containing, cow-milk-based infant formulas.     

Iron bioavailability from powdered and in-bottle-sterilized infant formulas in suckling and weanling rats

OBJECTIVE: The Maillard reaction and lactose isomerization may be induced during the manufacture of infant formulas. We studied the effects of dehydration and sterilization on iron bioavailability from an infant formula in suckling and weanling rats. METHODS: In experiment 1, a previously reconstituted powdered infant formula and an in-bottle-sterilized liquid infant formula from the same manufacturer were fed from drinking bottles to 2-wk-old suckling rat pups for 7 d. In experiment 2, the same formulas were complemented with AIN-76 and fed to weanling rats for 7 d after a 4-d adaptation period. In both experiments, intake, body weight, and fecal and urinary excretions were monitored, and the following iron indexes were calculated: apparent absorption and retention and the coefficients percentage of absorption versus intake, percentage of retention versus absorption, and percentage of retention versus intake. RESULTS: The liquid infant formula resulted in lower body weights on day 4, particularly among the younger rats that had significantly lower food intakes (P = 0.045). In weanling rats fed powdered and liquid infant formulas, food intake and body weight were not significantly different. The pups showed significantly higher absorption (percentage of absorption versus intake) and retention (percentages of retention versus absorption and retention versus intake) efficiencies than did the weanling rats (P < 0.001 for the three indexes). Hemoglobin values (P = 0.001) and liver iron concentrations (P = 0.009) were significantly higher in the weanling rats than in the pups. In contrast, erythrocyte iron concentrations and hematocrit were higher in the pups (P = 0.016 and 0.053, respectively). CONCLUSIONS: In rat pups, iron bioavailability is negatively affected by the consumption of in-bottle-sterilized infant formula, possibly as the result of the content of Maillard reaction products, altered proteins, and lactulose. However, when this formula is included in a mixed diet and given to weanling rats, this detrimental effect no longer occurs.     

Intrinsic and extrinsic labeling for studies of manganese absorption in humans

A dual-radioisotope method was used to simultaneously study whole-body manganese retention from a chicken liver based meal intrinsically labeled with 54Mn and extrinsically labeled with 52Mn. Manganese retention was monitored in a sensitive whole-body counter during approximately 30 d in six young adult women. Both radioisotopes were retained to a similar degree and excreted at identical rates. Retention at d 5 was 14.4 +/- 10.3 and 14.0 +/- 9.9% while retention at d 10 was 5.0 +/- 3.1 and 5.0 +/- 3.0% (X +/- SD) for 54Mn and 52Mn, respectively. From these results we conclude that the intrinsic and extrinsic Mn isotopes did form a common pool before absorption. The results can therefore be regarded as a direct validation of the use of extrinsic labeling for studies of Mn retention for estimating Mn absorption in man.     

Isolation and identification of Enterobacter sakazakii in infant milk formulas

Enterobacter sakazakii is a pathogen of increasing medical concern, due to it being implicated in cases of meningitis, sepis, and necrotizing enterocolitis associated with the consumption of contaminated infant milk formula. At present, the method adopted by the Mexican food industry for the isolation and identification of E. sakazakii is based on the methodology of the United States Food and Drug Administration (FDA). However, this procedure is laborious and requires 7 days to obtain a confirmative result. The objective of this study was to determine the presence of E. sakazakii in two types of powdered infant milk formula, using an alternative method that requires less time and a smaller sample size than the FDA protocol. We adapted Leuschner's procedure by eliminating violet red bile glucose agar (VRBG) plates and instead adopting white light incubation to stimulate yellow pigment development. This allowed for isolation of E. sakazakii from powdered infant milk formula using a smaller sample and requiring only 5 days for analysis. Results showed that 92% of formula 1 and 32% of formula 2 was positive for E. sakazakii. The high contamination level of E. sakazakii suggests the need for monitoring hygienic conditions in the manufacturing plant and to assess the prevalence of E. sakazakii in powdered infant milk formulas sold in México.     

A quantitative model for prediction of iron bioavailability from Indian meals: An experimental study

The major goal of the study was to explore the possibility of developing an updated model that integrates the effect of various enhancers and inhibitors for predicting the potential availability of iron from typical Indian vegetarian meals. The interaction effects of four constituents namely ascorbic acid, citric acid, tannic acid and calcium phosphate was studied using a standard cereal meal (STD meal) providing 3 mg non-heme iron/250 ml homogenate. Based on the data, a regression equation was evolved which was tested for its predictive power as applied to a set of 10 typical Indian meals. Regression analysis of the data revealed that both ascorbate and citrate emerged as equally strong enhancers while tannate and calcium phosphate demonstrated strong inhibitory effect on iron availability in the STD meal. Further, when the prediction equation, generated on the basis of the interaction effect data was applied to the typical Indian meals, it showed a high correlation coefficient (r = 0.76) between the analysed values for iron availability vs the values computed using the enhancer and inhibitor contents of the meals. Comparison with the only other model available in the literature namely that of Monsen & Balintfy (1982) revealed that the present model was far better in predicting iron availability from cereal based Indian meals (r = 0.76) than Monsen's model (r = 0.19). The findings of the present study substantiated the hypothesis that a regression model, evolved from a cereal meal, by integrating the effect of enhancers as well as inhibitors, rather than only enhancers, provides a more precise estimate of iron availability from typical Indian meals. A limitation of the model however, was that phytate could not be incorporated into the equation.     

Polyamines in human and rat milk and in infant formulas.

Polyamines are ubiquitous compounds known to be involved in cell proliferation and differentiation in many tissues. Enteral administration of these compounds has been shown to produce effects in suckling and adult animals. Using HPLC techniques, we verified the presence of putrescine, spermidine, and spermine in human milk and quantitated their concentration in samples collected from the first week up to 4 mo of lactation. Mean values of these compounds ranged (per liter) from 0 to 615 nmol putrescine, from 73 to 3512 nmol spermidine, and from 722 to 4458 nmol spermine. Polyamine concentrations in infant formulas were dependent on the protein source, the particular polyamine, and the protein concentration of the formula. Concentrations of these three compounds in rat milk over the first 3 wk of lactation were higher than in human milk, with spermidine being the polyamine most elevated compared with human milk (almost 20-fold higher). An artificial formula used for the rearing of suckling rats contained trace to immeasurable amounts of polyamines. Our study identifies milk as one vehicle for polyamine delivery to the intestinal mucosa of suckling animals.     

Plasma zinc and copper levels of infants fed different milk formulas

The plasma zinc and copper levels of 32 full-term healthy infants, aged 3-4 months, using different infant formulas, were measured. The plasma zinc levels of infants using soy formula (45.1 +/- 19.1 micrograms/dl) and iron-fortified cow's milk formula (61.6 +/- 12.9 micrograms/dl) were significantly lower than those of the infants using cow's milk formula not fortified with iron (77.5 +/- 13.4 micrograms/dl). The plasma copper levels of the infants using the different formulas were not significantly different from each other. Fortification of infant formulas with high levels of iron may reduce the zinc absorption from such formulas.     

Concentration and distribution of sialic acid in human milk and infant formulas

BACKGROUND: In animal studies, sialic acid supplementation is associated with increases of gangliosides in the brain and improved learning ability. Only limited data are available on the sialic acid content of human milk and infant formulas. OBJECTIVE: We compared the concentrations of oligosaccharide-bound, protein-bound, and free sialic acid in milk from mothers of full-term and preterm infants and in a range of infant formulas. DESIGN: The milk from 20 and 14 mothers of full-term and preterm infants (mean gestational age: 31 +/- 3 wk), respectively, was collected at 4 stages of lactation (colostrum, transition, 1 mo, and 3 mo) and compared with 21 different infant formulas. RESULTS: Total sialic acid concentrations were highest in colostrum (x +/- SEM: 5.04 +/- 0.21 mmol/L in full term) and decreased by nearly 80% over the next 3 mo. Human milk from mothers of preterm infants contained 13-23% more sialic acid than did milk from mothers of full-term infants at 3 of the 4 lactation stages (P < 0.02). The sialic acid content of most formulas was <25% of that found in mature human milk (P < 0.01). Most of the sialic acid in the formulas ( approximately 70%) was bound to glycoproteins, whereas in human milk most sialic acid was bound to free oligosaccharides. CONCLUSIONS: Human milk, including milk from mothers of preterm infants, is a rich source of oligosaccharide-bound sialic acid, which contrasts with the relatively small amounts found in infant formulas. The nutritional significance of sialic acid is presently unknown, but it is plausible that it is a conditional nutrient that contributes to sialic acid accretion in the brain.     

The effect of age on manganese uptake and retention from milk and infant formulas in rats

Manganese nutrition of the neonate is poorly understood, due in part to a paucity of information on the amount and availability of manganese in infant foods. We have developed a suckling pup model to assess the uptake of manganese from fluid diets by using extrinsic labeling. Human milk, cow milk and infant formulas were fed by intubation to fasted rat pups and adults. Rats were killed after varying time periods, and tissues were removed and counted. A period of 6 h was found to be adequate to allow for stomach emptying while limiting tissue redistribution; 24 h was found to reflect pup manganese retention. From human milk, manganese retention was highest (greater than or equal to 80%) in pups less than or equal to 15 days of age; in older pups average retention decreased to 40%. Using d 14 pups to assess relative Mn uptake from diets, wholebody Mn uptake was highest from cow milk (approximately 89%); uptake from human and cow milk formula was similar (approximately 80%) whereas it was lower from soy formula (approximately 60%). These findings suggest that bioavailability of Mn from infant diets is very high during the suckling period. Since most formulas contain considerably more manganese than is found in human milk, Mn deficiency may be less of a concern than possible toxicity from formulas.     

Different elemental infant formulas show equivalent phosphorus and calcium bioavailability in healthy volunteers

Retrospective chart reviews have reported hypophosphatemia associated with elemental formula use in infants and children with systemic disease involving multiple diagnoses. The present study aims to evaluate the bioavailability of phosphorus from 2 commercial elemental formulas and to test our hypothesis of bioequivalence of the 2 products in healthy volunteers receiving gastric acid-suppressive medication. A single-center, double-blind, randomized, cross-over study was conducted in healthy volunteers with esomeprazole-induced hypochlorhydria. After a standardized low phosphorus meal followed by overnight fasting, subjects consumed 1 gram of phosphorus in a single oral dose of 1217 kcal of Product A (Neocate) or Product B (Elecare). The alternate product was given following a 1-week washout period. Blood and urine were collected at baseline and different time-points for up to 6 hours after product consumption. Area-under-the-curve (AUC) and peak values (C_peak) for serum phosphate and calcium and urinary creatinine-corrected phosphate and calcium were assessed for bioequivalence of Products A and B. Results show that the geometric mean ratio (GMR) and 90% CI for serum phosphate were 1.041 (0.998-1.086) and 1.020 (0.963-1.080) for AUC_0-360 and C_peak, respectively, meeting the predetermined criteria for bioequivalence. Urinary creatinine-corrected phosphate followed a similar pattern after intake of Product A and B, but did not reach bioequivalence criteria (GMR: AUC_70-370 = 1.105 (0.918-1.330); C_peak = 1.182 (1.040-1.343)). Serum calcium concentrations (GMR: AUC_0-360 = 1.002 (0.996-1.009); C_peak = 0.991 (0.983-0.999)) and urinary creatinine-corrected calcium excretion (GMR: AUC_70-370 = 1.117 (1.023-1.219); C_peak = 1.157 (1.073-1.247)) demonstrated bioequivalence of the products. In conclusion, both elemental infant formulas showed equivalent serum phosphorus and calcium bioavailability in healthy volunteers even if combined with treatment with acid-suppressive medication.     

Tocopherols and tocotrienols in Finnish foods: human milk and infant formulas

Individual tocopherols and tocotrienols in human milk, mother's milk substitutes and other infant formulas have been determined by an HPLC method. 107 human milk samples (23 colostral, 22 transitional and 62 mature) obtained from six healthy mothers throughout the lactation were found to contain all the tocopherols, although delta-tocopherol occurred only in traces. A high content of alpha-tocopherol was found in colostrum (average 1.90 +/- 1.62 (SD) mg/100 g), as compared with transitional (0.65 +/- 0.22 mg/100 g) and mature milk (0.47 +/- 0.16 mg/100 g). The content of beta-tocopherol averaged 0.05 +/- 0.03, 0.02 +/- 0.01 and 0.02 +/- 0.01 and gamma-tocopherol 0.11 +/- 0.09, 0.07 +/- 0.04 and 0.07 +/- 0.04 mg/100 g in colostral, transitional and mature milk respectively. The alpha-tocopherol equivalents thus were 1.93, 0.66 and 0.49 mg/100 g; their ratios to the contents of polyunsaturated fatty acids meet the nutritional need of the newborn and young infant: 5.7, 2.1 and 1.4 mg/g in colostral, transitional and mature milk. Mother's milk substitutes and gruel and porridge powders are enriched with tocopherol acetate to vitamin E levels similar to or higher than those in human milk: substitutes contained on average 1.4 mg alpha-tocopherol equivalents/100 g and reconstituted powders 1.1 mg/100 g. The ratio of vitamin E to polyunsaturated fatty acids of these infant formulas was higher than the recommended value of 0.6 mg/g. The average values for alpha-tocopherol equivalents in fruit-berry and meat-vegetable infant formulas were 0.46 and 0.38 mg/100 g.     

Plasma zinc and copper levels of infants fed different milk formulas.

The plasma zinc and copper levels of 32 full-term healthy infants, aged 3-4 months, using different infant formulas, were measured. The plasma zinc levels of infants using soy formula (45.1 +/? 19.1 micrograms/dl) and iron-fortified cow's milk formula (61.6 +/? 12.9 micrograms/dl) were significantly lower than those of the infants using cow's milk formula not fortified with iron (77.5 +/? 13.4 micrograms/dl). The plasma copper levels of the infants using the different formulas were not significantly different from each other. Fortification of infant formulas with high levels of iron may reduce the zinc absorption from such formulas.     

Use of the net metabolizable energy values for labeling of infant formulas and foods—potential issues

The use of net metabolizable energy (NME) rather than metabolizable energy (ME) to determine energy values for food labeling has been suggested. A review was undertaken to determine issues that might arise if NME were applied to infant formulas and foods for infants.Both ME and NME factors derived from adult studies appear to be reasonably applicable to infants. Use of NME rather than ME values decreased the apparent energy density of human milk by about 4%; that of infant formulas, 4–6%. Even though the regulatory requirements for upper and lower limits of nutrients in infant formulas are expressed per 100 kJ or per 100 kcal, few significant issues would be expected based on a change in the declared energy content of this magnitude. Energy content of representative baby foods decreased 2–9%. The regulatory implications of using NME are at least a requirement to relabel virtually all products.The use of NME as it relates to selection of a healthy diet for infants, scientific validity, comparability of food energy values and requirements, interproduct comparisons and facilitation of trade are briefly addressed. It is recommended that factors used to calculate food energy in infant formula and foods for infants and small children be consistent with those used for other foods.