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Background: Phytic acid (PA) is a major inhibitor of iron bioavailability from beans, and high PA concentrations might limit the positive effect of biofortified beans (BBs) on iron status. Low-phytic acid (lpa) bean varieties could increase iron bioavailability., Objective: We set out to test whether lpa beans provide more bioavailable iron than a BB variety when served as part of a composite meal in a bean-consuming population with low iron status., Methods: Dietary iron absorption from lpa, iron-biofortified, and control beans (CBs) (regular iron and PA concentrations) was compared in 25 nonpregnant young women with low iron status with the use of a multiple-meal crossover design. Iron absorption was measured with stable iron isotopes., Results: PA concentration in lpa beans was ∼10% of BBs and CBs, and iron concentration in BBs was ∼2- and 1.5-fold compared with CBs and lpa beans, respectively. Fractional iron absorption from lpa beans [8.6% (95% CI: 4.8%, 15.5%)], BBs [7.3% (95% CI: 4.0%, 13.4%)], and CBs [8.0% (95% CI: 4.4%, 14.6%)] did not significantly differ. The total amount of iron absorbed from lpa beans and BBs was 421 μg (95% CI: 234, 756 μg) and 431 μg (95% CI: 237, 786 μg), respectively, and did not significantly differ, but was >50% higher (P < 0.005) than from CBs (278 μg; 95% CI: 150, 499 μg). In our trial, the lpa beans were hard to cook, and their consumption caused transient adverse digestive side effects in ∼95% of participants. Gel electrophoresis analysis showed phytohemagglutinin L (PHA-L) residues in cooked lpa beans., Conclusion: BBs and lpa beans provided more bioavailable iron than control beans and could reduce dietary iron deficiency. Digestive side effects of lpa beans were likely caused by PHA-L, but it is unclear to what extent the associated digestive problems reduced iron bioavailability. This trial was registered at clinicaltrials.gov as NCT02215278., (© 2016 American Society for Nutrition.)

Iron bioavailability from common beans is negatively influenced by phytic acid (PA) and polyphenols (PPs). Newly developed low-PA (lpa) beans with 90% less PA and variable PPs might improve iron bioavailability. The aim of this study was to evaluate the influence of lpa beans on iron bioavailability in women (n = 20). We compared iron absorption from 4 different beans using a paired, double meal, crossover design. Iron absorption was measured as erythrocyte incorporation of stable iron isotopes (Fe(57), Fe(58)) from 2 lpa bean lines, one high in PPs (means ± SDs; PA = 124 ± 10 mg/100 g; PPs = 462 ± 25 mg/100 g) and one low in PPs (PA = 70 ± 10 mg/100 g; PPs = 54 ± 2 mg/100 g). The other 2 beans used were their parents with a normal PA concentration, one high in PPs (PA = 1030 ± 30 mg/100 g; PPs = 676 ± 19 mg/100 g) and one low in PPs (PA = 1360 ± 10 mg/100 g; PPs = 58 ± 1 mg/100 g). Fractional iron absorption from the lpa bean high in PPs was 6.1% (95% CI: 2.6, 14.7), which was 60 and 130% higher compared with the parent high in PPs (P < 0.001) and low in PPs (P < 0.001), respectively. The total amount of iron absorbed per test meal from the lpa bean high in PPs (372 μg; 95% CI: 160, 890) was 60 and 163% higher compared with the parent high in PPs (P < 0.001) and low in PPs (P < 0.001), respectively. Fractional iron absorption from the lpa line low in PPs (4%; 95% CI: 1.8, 8.7) was 50% higher and the total amount of iron absorbed per test meal (261 μg; 95% CI: 120, 570) was 85% higher than iron from the parent low in PPs (P < 0.001). There was no difference between the lpa beans high or low in PPs or between the parents high or low in PPs. A 90% reduction in PA leads to an increase in bioavailable iron from beans, independent of the PP concentration. The lpa mutation could be a key tool for improving iron bioavailability from beans.

Cowpeas, like other legumes, contain high amounts of native iron but are rich in phytic acid (PA) and polyphenols (PP) that inhibit iron absorption. NaFeEDTA may overcome the combined inhibitory effect of PA and PP. Our objective was to test the efficacy of NaFeEDTA-fortified cowpea meal in improving iron status of school children in a malaria endemic area. We conducted a double-blind, controlled trial with 5- to 12-y-old school children from 2 rural communities in northern Ghana (n = 241). Eligible children were randomly assigned to 2 treatment groups to receive either cowpea meal fortified with 10 mg Fe/meal as NaFeEDTA, or an identical but nonfortified cowpea meal. Meals were provided 3 d/wk for a period of ~7 mo under strict supervision. Mass deworming and malaria antigenemia screening and treatment were carried out at baseline and 3.5 mo into the trial. Consumption of cowpea flour fortified with NaFeEDTA resulted in improvement of hemoglobin (P < 0.05), serum ferritin (P < 0.001), and body iron stores (P < 0.001) and reduction of transferrin receptor (P < 0.001) compared with nonfortified flour. Fortification resulted in a 30 and 47% reduction in the prevalence of iron deficiency (ID) and iron deficiency anemia (IDA) (P < 0.05), respectively. The results indicate that fortification of cowpea flour with NaFeEDTA overcomes the combined inhibitory effect of PA and PP and, when used for targeted school-based fortification of cowpea flour, is effective in reducing the prevalence of ID and IDA among school children in malaria endemic rural northern Ghana.

Biofortification of plants is a new approach to combat iron deficiency. Common beans (Phaseolus vulgaris) can be bred with a higher iron concentration but are rich in iron absorption inhibitors, phytic acid (PA), and polyphenols (PP). To evaluate the potential of beans to combat iron deficiency, three iron absorption studies were carried out in 61 Rwandese women with low iron status. Studies 1 and 2 compared iron absorption from high and low PP beans, similar in PA and iron, fed as bean puree in a double meal design or with rice and potatoes as multiple meals. Study 3 compared iron absorption from high and normal iron beans with similar PP levels and a PA:iron molar ratio, fed with potatoes or rice in multiple meals. Iron absorption was measured as erythrocyte incorporation of stable iron isotopes. In study 1, iron absorption from the high PP bean (3.4%) was 27% lower (P < 0.01) than from low PP bean (4.7%), but when fed in multiple meals (study 2), there was no difference (7 and 7.4%, respectively; P > 0.05). In study 3, iron absorption from the high iron bean (3.8%) was 40% lower (P < 0.001) than from the normal iron bean (6.3%), resulting in equal amounts of iron absorbed. When beans were combined with other meal components in multiple meals, high PP concentration had no negative impact on iron absorption. However, the quantity of iron absorbed from composite meals with high iron beans was no higher than with normal iron beans, indicating that efficacious iron biofortification may be difficult to achieve in beans rich in PA and PP.

Low iron absorption from common beans might contribute to iron deficiency in countries where beans are a staple food. High levels of phytic acid (PA) and polyphenols (PP) inhibit iron absorption; however, the effect of bean PP on iron absorption in humans has not been demonstrated and, with respect to variety selection, the relative importance of PP and PA is unclear. To evaluate the influence of bean PP relative to PA on iron absorption in humans, 6 stable iron isotope absorption studies were conducted in women (16 or 17 per study). Bean PP (20, 50, and 200 mg) were added in studies 1-3 as red bean hulls to a bread meal. Studies 4- 6 investigated the influence on iron absorption of PP removal and dephytinization of whole red bean porridge and PP removal from dephytinized porridge. Iron absorption was lowered by 14% with 50 mg PP (P < 0.05) and by 45% with 200 mg PP (P < 0.001). The mean iron absorption from whole bean porridge was 2.5%. PP and PA removal increased absorption 2.6-fold (P < 0.001) and removal of PP from dephytinized porridge doubled absorption (P < 0.001). Between-study comparisons indicated that dephytinization did not increase iron absorption in the presence of PP, but in their absence, absorption increased 3.4-fold (P < 0.001). These data suggest that in countries where beans are a staple food, PP and PA concentrations should be considered when selecting bean varieties for human consumption. Lowering only one inhibitor will have a modest influence on iron absorption.

Nutritional rickets resulting from calcium insufficiency is common in Nigeria and high dietary phytate is thought to inhibit calcium and zinc absorption. We compared the effects of a high-phytate meal and enzymatic dephytinization on calcium and zinc absorption in Nigerian children with and without rickets. Nineteen children with rickets and 15 age-matched control children, aged 2-10 y, were given calcium (600 mg/d) and ergocalciferol (1250 microg/wk). After 6 wk, calcium and zinc absorption were measured in both groups with and without maize porridge using stable isotopes. One week later, absorption measurements were repeated to assess the effects of enzymatic dephytinization and fermentation of the maize porridge. The phytate concentration of maize porridge (3.87 +/- 0.38 g/kg wet weight) was reduced by enzymatic dephytinization (2.83 +/- 0.41 g/kg; P < 0.001) but not by fermentation (3.35 +/- 0.27 g/kg; P = 0.08). Calcium and zinc absorption were unaffected by the presence of rickets or by fermentation of maize porridge. Calcium absorption was greater with a meal (61.3 +/- 25.1%) than without (27.8 +/- 14.6%; P < 0.001). Zinc absorption was lower with a meal (16.2 +/- 8.0%) than without (63.4 +/- 23.9%; P < 0.001). Enzymatic dephytinization increased relative zinc absorption from a meal by 101 +/- 81% (P < 0.001) but did not affect calcium absorption. Rickets was not associated with impaired calcium or zinc absorption. Calcium absorption was enhanced by maize porridge, but zinc absorption was reduced. Enzymatic dephytinization increased zinc absorption. Multiple strategies may be required to optimize calcium and zinc absorption in deficient populations.

Searching for economical, nonconventional sources of iron is important in underdeveloped countries to combat iron deficiency and anemia. Our objective was to study iron, vitamin C, and phytic acid composition and also iron bioavailability from 4 species of marine algae included in a rice-based meal. Marine algae (Ulva sp, Sargassum sp, Porphyra sp, and Gracilariopsis sp) were analyzed for monthly variations in iron and for ascorbic acid and phytic acid concentrations. A total of 96 subjects received rice-based meals containing the 4 species of marine algae in different proportions, raw or cooked. All meals contained radioactive iron. Absorption was evaluated by calculating the radioactive iron incorporation in subjects' blood. Iron concentrations in algae were high and varied widely, depending on the species and time of year. The highest iron concentrations were found in Sargassum (157 mg/100 g) and Gracilariopsis (196 mg/100 g). Phytates were not detected in the algae and ascorbic acid concentration fluctuated between 38 microg/g dry weight (Ulva) and 362 microg/g dry weight (Sargassum). Algae significantly increased iron absorption in rice-based meals. Cooking did not affect iron absorption compared with raw algae. Results indicate that Ulva sp, Sargassum sp, Porphyra sp, and Gracilariopsis sp are good sources of ascorbic acid and bioavailable iron. The percentage of iron absorption was similar among all algae tested, although Sargassum sp resulted in the highest iron intake. Based on these results, and on the high reproduction rates of algae during certain seasons, promoting algae consumption in some countries could help to improve iron nutrition.

Calcium (Ca)-fortified soymilk has gained popularity in the United States. Tricalcium phosphate (TCP)-fortified soymilk was shown to have a lower Ca bioavailability than cow's milk in men. However, the most popular soymilk in the U.S. is fortified with Ca carbonate (CC) and has not been evaluated. Ca bioavailability from CC-fortified soymilk (CCSM) and TCP-fortified soymilk (TCPSM) was compared with cow's milk in young healthy women using the dual stable isotope technique. In a 3-way crossover design, 20 volunteers (23 +/- 2 y old) consumed 250 mg Ca in cow's milk, CCSM, or TCPSM along with 10 mg 44Ca after an overnight fast. Cow's milk was extrinsically labeled, whereas each fortified soymilk was intrinsically labeled with each chemical salt of 44Ca at the manufacturing facility. Another stable isotope, 43Ca, was injected i.v. 1 h after the complete consumption of cow's milk or soymilk. Fractional Ca absorption was determined from the ratios of 43Ca:42Ca and 44Ca:42Ca by inductively coupled plasma (ICP)-MS in the 24-h urine samples. A mixed linear model (SAS proc mixed) was used to compare the fractional Ca absorption among groups. Fractional Ca absorption in CCSM (0.211 +/- 0.057) did not differ from that of cow's milk (0.217 +/- 0.040), but both were higher (P < 0.05) than that of TCPSM (0.181 +/- 0.039). Our result suggests that calcium absorption is equivalent for CCSM and cow's milk at similar calcium loads.

Populations that depend on grains and legumes as staple foods consume diets rich in phytic acid (myo-inositol-1,2,3,4,5,6-hexkisphosphate), the storage form of phosphorus in seeds. This compound binds tightly to important mineral nutrients such as iron and zinc, forming salts that are largely excreted. This phenomenon can contribute to mineral depletion and deficiency. As one approach to solving this and environmental problems associated with seed-derived dietary phytic acid, the U. S. Department of Agriculture and others have isolated cereal and legume low-phytic acid mutations and have used these to breed first-generation low-phytate hybrids, cultivars and lines of maize (Zea mays), barley (Hordeum vulgare), rice (Oryza sativa) and soybean (Glycine max). Seed phytic acid is reduced in these crops by 50-95%. The progress in the genetics, breeding and nutritional evaluation of low-phytate crops are reviewed in this article.

Modern genetic and molecular technologies provide a number of tools that can be utilized for the development of staple foods with a higher iron and zinc content and improved bioavailability of these minerals. This article summarizes current strategies aimed at increasing the iron-sequestering capacity of the endosperm and improving mineral bioavailability via in planta synthesis of microbial phytases. A case study is presented for wheat, and future strategies are discussed addressing the importance of phytase thermostability.

As the search for alternative sources of food to alleviate hunger continues, this study was undertaken to determine the biological value in growing rats (BV) of proteins of some lesser known tropical seeds gathered in Nigeria. Antinutritional factors (trypsin inhibitors, phytic acid, oxalate, tannin, alkaloids) and amino acid compositions were also determined, and protein digestibility-corrected amino acid score (PDCAAS) was calculated using the amino acid requirement pattern of the preschool child and individual seed-specific correction factors for crude protein. A rat growth and balance study was conducted to determine digestibility, nitrogen-, and energy balance by feeding as the only unsupplemented protein source milled and heat-treated seeds of Adansonia digitata (Bombacaceae) and Prosopis africana, Lonchocarpus sericeus, Enterolobium cyclocarpium, Sesbania pachycarpa and Pterocarpus osun (Leguminosae) in comparison to casein fortified with methionine (control). Diets containing P. africana and L. sericeus seeds caused poor feed intake and weight loss in rats and were excluded from the nitrogen-balance test. Among the seed samples, S. pachycarpa followed by A. digitata showed the most advantageous nutritional quality [amino acid composition, digestibility, BV and net protein utilization (NPU)]. True digestibility was 82.9 and 74.5 vs. 98.5, BV was 64.6 and 70.0 vs. 90.4, and NPU was 53.5 and 52.1 vs. 89.0 for S. pachycarpa and A. digitata vs. casein (control), respectively. In terms of PDCAAS, lysine was the first limiting amino acid for S. pachycarpa (88%) and for A. digitata (58%). The PDCAAS of all essential amino acids was below 100% for E. cyclocarpium (e.g., cysteine + methionine: 37%) and for P. africana (e.g., threonine: 46%, except valine and a very high content of cysteine and methionine). In conclusion, all seeds tested in the rat balance trial were of inferior quality compared to casein. Before these tropical seeds could be used as food components or feed supplements, safety studies and proper processing to remove antinutritional factors and possible toxic constituents were required.

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.

One important aspect of the safety assessment of genetically engineered crops destined for food and feed uses is the characterization of the consumed portion of the crop. One crop currently under development, glyphosate-tolerant soybeans (GTS), was modified by the addition of a glyphosate-tolerance gene to a commercial soybean cultivar. The composition of seeds and selected processing fractions from two GTS lines, designated 40-3-2 and 61-67-1, was compared with that of the parental soybean cultivar, A5403. Nutrients measured in the soybean seeds included macronutrients by proximate analyses (protein, fat, fiber, ash, carbohydrates), amino acids and fatty acids. Antinutrients measured in either the seed or toasted meal were trypsin inhibitor, lectins, isoflavones, stachyose, raffinose and phytate. Proximate analyses were also performed on batches of defatted toasted meal, defatted nontoasted meal, protein isolate, and protein concentrate prepared from GTS and control soybean seeds. In addition, refined, bleached, deodorized oil was made, along with crude soybean lecithin, from GTS and control soybeans. The analytical results demonstrated the GTS lines are equivalent to the parental, conventional soybean cultivar.

Phytate is an inhibitor of iron absorption that can be removed before the intestinal site of absorption by microbial phytase, thereby increasing iron absorption from a meal. The effects of two kinds of dietary phytase, cereal phytase and microbial phytase from Aspergillus niger, on iron absorption were investigated. Iron absorption was measured from single meals containing white wheat rolls supplemented with wheat bran with or without phytase activity (expt. 1) and phytase-deactivated wheat bran with or without addition of microbial phytase from A. niger (expt. 2). Each experiment had 10 subjects and two different radio iron tracers: 55Fe and 59Fe were used for comparison of the absorption from the test meals in each experiment. No differences in iron absorption were found between meals containing wheat brain with or without phytase activity. Addition of microbial phytase to the meal containing phytase-deactivated wheat bran increased iron absorption from 14.3 +/- 2.6% to 26.1 +/- 3.8% (P < 0.0001). Two pH optima, one at pH 2.0 and one at pH 6.0, were found for A. niger phytase at 37 degrees C, but activity occurred at all pH values between 1.0 and 7.5. The results suggest that effective and complete degradation of phytate occurred in the stomach when A. niger phytase was given with the meal. This may be explained by high activity of microbial phytase at physiological pH conditions of the stomach, whereas wheat phytase has a different pH optimum.

Soybeans are high in protein but also contain a number of minor constituents traditionally considered to be antinutritional factors. These include trypsin inhibitors, phytic acid, saponins and isoflavones. These compounds are now thought to have beneficial biological effects in the diet, such as lowering blood cholesterol or preventing cancer. Soybean processing changes the content of these minor constituents in various ways. This review discusses the changes in content of trypsin inhibitors, phytic acid, saponins and isoflavones as soybeans are processed into the conventional protein ingredients, flours, concentrates and isolates, as well as some of the traditional Oriental soybean foods.

These studies were conducted to determine if supplementation of a corn-soybean meal diet with 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] would increase the utilization of natural phytate phosphorus by broiler chickens. Two experiments were conducted to evaluate the effect of dietary 1,25-(OH)2D3 in the presence and absence of supplemental phytase and at several dietary levels of inorganic phosphorus supplementation. The criteria measured in these studies were weight gain, gain:feed ratio, bone ash, rickets due to phosphorus deficiency, plasma calcium and phosphorus and retention of calcium, phosphorus and phytate phosphorus. In the first experiment, the types and amounts of fecal inositol phosphates were determined by HPLC, and the total fecal phytate was determined by the classic FeCl3 precipitation technique. In the first experiment, the addition of 1,25-(OH)2D3 to the diet in the presence of dietary phytase resulted in greater 9-d weight and bone ash and lower incidence of rickets; the retention of total fecal phytate and phytate phosphorus was greater than in controls. The second experiment was a complete 2 x 2 x 2 factorial design [phosphorus levels x phytase x 1,25-(OH)2D3]. The addition of 1,25-(OH)2D3 alone to the diet resulted in greater 9-d weight and bone ash, lower incidence of rickets, and greater retention of total calcium and phosphorus and phytate phosphorus. The highest retention of phytate phosphorus (79.4%) was obtained when both phytase and 1,25-(OH)2D3 were present in the diet. The possible mode of action and importance of these results in many areas of nutrition and environmental science are discussed.

The inhibitory effect of phytic acid in soybean products on zinc bioavailability was evaluated in two experiments in rats. In Experiment 1, soybean flours containing different natural phytic acid levels produced by sand culture techniques that limited phosphorus during growth of the soybean plants were formulated into diets. The rats fed a higher phytic acid level diet had lower food intake, depressed weight gain, and lower tibia zinc gain (P < 0.05). A negative, linear relationship between tibia zinc gain and dietary phytic acid level was found. In Experiment 2, two commercially produced soybean isolates containing either normal phytic acid level or a reduced level were formulated into diets. Slope ratio analysis revealed that relative zinc bioavailability from phytic acid-containing soybean isolate-based diets was significantly reduced (P < 0.05) compared with control diets. Reduced phytic acid soybean isolate-containing diets resulted in a significant increase of zinc bioavailability compared with normal phytic acid diets (P < 0.01). These results coupled with other reports indicate that phytic acid is the primary inhibitory factor in soybean products that results in reduced zinc bioavailability and that phytate reduction in soybean protein increases zinc bioavailability.

To investigate the digestion of phytate in the stomach and small intestine in humans, studies were performed in subjects with established ileostomy. A recently developed high performance liquid chromatography method made it possible to analyze phytate and its degradation products in food and digesta. The digestibility of phytate in raw bran and extruded bran was investigated in seven ileostomy patients. Each subject was studied for two 4-d periods while consuming a constant low fiber diet with the addition of either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. During passage through the subject's stomach and small intestine 58%, on average, of the phytate in unprocessed bran was hydrolyzed to inositol penta-, tetra- and triphosphates. When bran was subjected to extrusion cooking, 25% of the inositol hexaphosphate was hydrolyzed to penta- and tetraphosphate and the phytase activity ceased. Essentially no phytate digestion occurred when the ileostomy subjects consumed the extruded product. The reduced digestibility might be due to the lost phytase activity or to formation of indigestible phytate complexes during extrusion cooking.

The purpose of this study was to investigate whether dietary phytase is involved in the hydrolysis of phytate in the stomach and small intestine of humans. The digestibility of phytase-deactivated wheat bran was studied on eight occasions and untreated wheat bran on two occasions in healthy ileostomates. Five subjects were studied for two 4-d periods and one subject on two occasions for two 4-d periods while fed a constant low fiber diet. The low fiber diet was supplemented with 16 g/d wheat bran in the second period. Three other subjects fed a low fiber diet were studied for 10 consecutive days, bran being added to the diet on d 5, 6 and 7. Inositol hexaphosphate and its degradation products were analyzed with a recently developed HPLC method. On average, 95% of the ingested phytate from phytase-deactivated wheat bran and 40% of the ingested phytate from untreated wheat bran were recovered in ileostomy contents. These results differ from those of a previous analysis using an iron precipitation method. Mucosal phytase and alakaline phosphatase, if present in the human small intestine, do not seem to play a significant role in phytate digestion in humans, whereas the dietary phytase may be an important factor for phytate hydrolysis. Iron precipitation methods are not adequate for determinations of phytate digestion.

Zinc availability from a series of foods was determined using 65Zn-labeled test meals fed to rats. Zinc availability relative to zinc chloride depended on the amount of the zinc source in the test meal. Zinc availability from several foods was similar to that from zinc chloride when tested in smaller amounts, but enhanced when fed in larger amounts. The range of zinc availability was similar for foods of plant and animal origin. Rats retained significantly more zinc from pork, chicken, peanut butter, egg or milk than from rice, beef, soybean flour or navy beans. Foods with intermediate zinc availability were sweet corn, whole wheat bread, cheese and oysters. Several food characteristics were examined for possible relationships with zinc availability, including the solubility or molecular size of zinc compounds after an in vitro enzymatic digestion and the contents of phytic acid, minerals, amino acids, carbohydrate and fatty acids relative to the zinc content of the food. Protein and several amino acids predicted about half of the variance in zinc availability. Following in vitro enzymatic digestion, neither zinc solubility nor the partitioning of zinc between low and high molecular weight substances was a strong predictor of zinc availability.

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.

Experiments were carried out to determine the effects of endogenous phytic acid in soybean seeds (Glycine max, var. "Amsoy") on the bioavailability of 59Fe to iron-depleted rats. Soybean plants were grown in nutrient solutions labeled with 59Fe supplied at either 0.4 or 1.0 ppm iron in solution. Immature and mature soybean seeds were harvested and fed to male rats as a single dose. The phytic acid content of the immature and mature seeds averaged 0.61 and 1.71% dry weight, respectively. Varying the nutrient solution iron concentration in the mature soybean seeds. When the 59Fe-labeled seeds were fed to iron-deficient rats, 59Fe from the mature seeds was more available than that from immature seeds even though the mature seeds contained approximately three times as much phytic acid. Autoclaving the mature seeds did not affect the absorption of 59Fe by rats from the seeds. Immature soybean seeds contained much more insoluble 59Fe than did mature soybean seeds. It was concluded that the directly correlated to the phytate content of the seeds; also immature soybean seeds apparently contain a factor or factors (other than phytic acid) that depresses iron availability.

Male rats were used to assess the availability of zinc in soybean seeds (Glycine max, var. 'Amsoy') as affected by maturity of seed, dietary protein source, and exogenous dietary sodium phytate. Seeds were harvested from either 84- (immature) or 120-day-old (mature) plants grown in 65Zn-labeled nutrient solutions that contained either 0.066 or 0.262 ppm zinc as zinc sulfate. Increased zinc supply to plants increased the zinc content of seeds; immature seeds had higher concentrations of zinc than mature seeds. Phytic acid concentration averaged about 0.6 and 1.7% dry weight in immature and mature seeds, respectively. Seeds of each type were incorporated into meals fed to zinc-depleted rats. In experiment 1, rats fed mature, high-phytate seeds absorbed about 60% of the 65Zn in the seeds, whereas rats fed immature, low-phytate seeds absorbed about 89% of the 65Zn (P less than 0.05). In experiment 2, the source of dietary protein (egg albumen or soy protein) did not markedly affect 65Zn absorption by rats fed mature soybean seeds. In experiment 3, dietary sodium phytate (1.76% of diet as phytic acid) depressed (P less than 0.05) 65Zn absorption by about 16 and 44% from mature soybean seeds and zinc sulfate, respectively. Zinc in soybean seeds apparently was as readily available to rats as that reported for other legume and cereal seeds. Moreover, the nutritional quality of soybean seeds with respect to zinc apparently can be increased by increasing zinc supplies to plants.

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.

Low-phytate wheat bran was produced by enzymatic hydrolysis and extraction. Rat bioassay methods were utilized to determine bioavailability of iron and zinc in the low-phytate brans and to study the effect of dietary phytate/zinc molar ratio on zinc bioavailability when the phytate source was bran. Endogenous phytase activity hydrolyzed 80-100% of the phytate when wheat bran was incubated in water overnight. The relative biological values of the iron in raw bran and phytate-free bran were 98 and 113, respectively, compared to 100 for ferrous ammonium sulfate in a hemoglobin repletion assay. Low-phytate brans with phytate/zinc molar ratios of 8 or less were equivalent to zinc sulfate as dietary sources of zinc for growth of rats. Rats fed diets that contained wheat bran with zinc sulfate added to reduce the dietary phytate/zinc molar ratio from 40 or 50 to 20 grew at the same rate as rats fed a phytate-free diet, but femur zinc values were lower than those in the reference group. Gel filtration chromatography of extracts of raw and low-phytate brans suggested that zinc might be associated with phytate in wheat bran.