Phytate wheat

Phytate, Wheat Bran, and Bioavailability of Dietary Iron... 

Agte V V and Joshi S R (1997), Effect of traditional food processing on phytate degradation in wheat and millets , J Agric Food Chem, 45,1659-1661. 

Two metabolic balance studies were conducted using healthy adult men to study the effect of phytate on bioavailability of dietary calcium. Dietary treatments were each 15 days in duration. In the first study, a mean daily calcium balance of 208+58 (SD) mg was observed when 2.0 g of phytate from 36 g of whole wheat bran was consumed daily with 1100 mg of calcium, phytate/calcium molar ratio 0.11. Calcium balance was 184+87 mg when 36 g of dephytinized bran was consumed with the same intake of calcium, phytate/calcium molar ratio 0.01. In the second study, calcium intake was 740 mg/day. 

Two metabolic balance studies conducted in our laboratory have yielded information relative to the effect of phytate and dietary fiber on calcium bioavailabilty. In the first study, a relatively high intake of dietary fiber was consumed with a 10-fold difference in phytate intake from wheat bran. In the second study three levels of phytate were consumed with a low amount of dephytinized bran as the principal dietary fiber source. The two higher phytate levels in the latter study were attained using sodium phytate. 

The diet treatments were level of phytate intake, either 0.2 or 2.0 g/day. Each level was consumed for 15 days, three consecutive repeats of the 5-day menu cycle. To provide 2.0 g/day of phytic acid, 36 g of wheat bran was baked into 6 muffins and two muffins were eaten each meal. Dephytinized bran was prepared by incubating the bran in water and allowing the endogenous phytase to hydrolyze the phytate, then the entire incubation mixture was freeze-dried (4) and 36 g baked into 6 muffins. Thus, the intake of all nutrients and neutral detergent fiber was the same for both phytate intakes. Five subjects consumed the whole bran muffins for 15 days followed by the dephytinized bran muffins for 15 days and the other 5 subjects in the reverse order. Brilliant blue dye was given at breakfast on the first day of each collection period to aid in demarcation of stools. Stool composites were made for days 1-5, 6-15, 16-20 and 21-30 and urine composites for days 6-15, and 21-30. Daily food composites were made, homogenized, freeze-dried and then analyzed to determine mineral nutrient intakes. 

The brown or whole meal bread diets employed by previous investigators were often variable in calcium and phytate intakes, not only between individuals, but by the same individual subjected to different diet treatments. Nevertheless an estimate of the molar ratio of phytate/calcium in the brown or whole meal bread diets used by McCance and Widdowson (UO), Walker et al. (11) and Reinhold et al. (2, 12) is 0.25 or greater. These investigators observed either negative or less positive calcium balance and apparent absorption when the brown bread diets were consumed compared to white bread diets with phytate/calcium molar ratios less than 0.05. Our results support their findings. Reinhold et al. (2) and McCance and Widdowson (33) used sodium phytate in some studies as well as whole wheat bread and observed similar results. 

Our studies do not resolve the question of phytate vs fiber for the effect of wheat bran on dietary calcium bioavailability. Phytate level clearly affected apparent absorption of calcium in HS-II in the presence of an amount of the water insoluble fraction of dephytinized bran equivalent to 12 g of untreated bran and the phytate supplied as sodium phytate. An additional trial using untreated bran and the same amount of fiber as the water insoluble fraction with sodium phytate could resolve the question of fiber vs phytate. In HS-I, the balances were positive when a relatively large amount of bran, 36 g/day, was consumed. Calcium intakes were possibly higher than most men consume, but under the dietary conditions imposed for 15 days, the phytate and fiber of 36 g of bran did not express an adverse effect on calcium balance. 

Wheat bran has been the fiber source most commonly used to study effects of dietary fiber on calcium absorption in controlled laboratory studies. However, wheat bran and other forms of fiber as they occur in food products present several disadvantages in terms of definition and by concurrently altering intakes of other substances or materials known or suspected of having an adverse effect on the bioavailability of calcium such as phytates and oxalates (5,13,17,22-28). Several studies have been conducted which have sought to separate or compare the effects of phytate and fiber... 

Hallberg, L. (1987). Wheat fiber, phytates and iron absorption. Scand. J. Gastroenterol. Suppl. 129, 73-79. 

Inhibitory effect of wheat fibre extract on calcium absorption in Caco-2 cells evidence for a role of associated phytate rather than fibre per se. Eur J Nutr 2000 39(1) 12-17. 

Other workers (115-124 for example) have also centered their efforts on the role of phytic acid on zinc and iron bioavailabiliy from both soy and wheat products. It has been suggested (120) that the phytate-to-zinc molar ratio could be used to predict zinc bioavailability in high-phytate foods. Several groups (115, 117), including ours (113), 1 least partially supporT this hypothesis. However, recent work from our laboratory (112) involving soy protein of similar phytate-to-zinc molar ratios clearly demonstrates that zinc bioavailability is also altered by food processing. In this study, zinc from neutralized soy concentrates and isolates was shown to be less available to the rat than was the corresponding acid-precipitated products. This is unfortunate as alkaline conditions are commonly utilized for soy and other plant proteins to obtain beneficial functional properties. 

Zinc Deficiency. A nutritional problem associated with consumption of large amounts of whole wheat products is the unavailability of dietary zinc, first observed in a patient with immature development and dwarfism in southern Iran (17). The patient showed marked improvement when placed on a well-balanced, nutritious diet for a year. In 1962, similar patients were observed in Egyptian villages. A deficiency of zinc was identified as the primary reason for the development of this condition. This deficiency of zinc results from the binding of that metal by the phytates present in whole wheat (18). Even when an excess of zinc is present in the diet, if conditions are right, that zinc may be complexed with the phytate and thus rendered unavailable to the body (see Mineral nutrients). Thus, a zinc deficiency may develop when its dietary level appears adequate but the diet contains large amounts of a food, such as whole wheat, that is high in phytates. 

Bioavailability of nutrients may be influenced beneficially or adversely by pelleting. For example, the availability of phytate phosphorus in grains was found to be increased by steam-pelleting (Bayley et al., 1975). On the other hand, there may be destruction of heat-labile nutrients and components, such as phytase enzyme in wheat or vitamin A. 

Phytate has been studied extensively with regard to mineral (mostly Zn and Ca) status of animals, and it has been shown to reduce whole-body Mn retention in rats (12). Phytate, however, is not present in the neutral detergent fiber or in the ash component of feedstuffs. Therefore, phytate does not appear to be responsible for the reduction of Mn uptake in chicks fed corn, soybean meal, wheat bran or fish meal (9). That phytate negatively impacts Mn nutriture also disagrees with the research of Reinhold et aK (13), who reported that fiber, and not phytate, was the pTTmary factor determining bioavailability of divalent mineral elements in breads. 

Wheat bran and whole wheat cereals quantitatively contain high amounts of manganese and are often listed as particularly valuable sources of manganese. However, zinc also is contained in appreciable amounts in wheat bran and whole wheat products but is poorly absorbed by the human from these sources. This has been attributed to either the phytate or the fiber contents of these products or a combination of these two dietary factors. These same factors may also affect the absorption of manganese. 

As shown on Table III, the subjects fed 20 g of hemicellulose from purified psyllium fiber excreted significantly more manganese in the feces than when they were fed bread without the hemicellulose supplement. Unlike wheat bran, purified psyllium fiber (sold commercially as a bulk laxative) contains no manganese or phytates hence, any change in fecal manganese excretion when psyllium fiber is added to human diets can probably be credited to the mixture of hemicellulose comprising this product. 

This association is greatest at the isoelectric point of the protein and being readily dissociated at pH s above or below the isoelectric point ( iJ.) Phytate association in cereal grains is less well defined but is contained in significant concentrations both in the bran and germ (12). There appears to be at least one ferric ion associated in the otherwise soluble phytate complex in wheat bran (13). Phytate in sesame seed appears to be the most unique and least soluble of all seeds. In this case magnesium appears to be the predominant cation (9 ) ... 

The effect on zinc balance of a 10-fold difference in dietary molar ratio of phytate/zinc was tested in a metabolic balance study with 10 adult men. The mean zinc balance was 2.7 mg per day vrtien the dietary molar ratio of phytate/zinc was about 12 and 2.0 mg per day when the ratio was about 1. Menus consisted of foods commonly consumed in the United States. The mean daily intake of zinc was 17 mg and of neutral detergent fiber 16 g. The molar ratios of phytate/zinc were attained by using 36 g per day of whole or dephytinized wheat bran. Analysis of hospital and self-chosen diets Indicate that the majority of the United States population consume diets with molar ratios of phytate/zinc less than 10, but which provide less than the recommended dietary allowance of zinc. The balance results are discussed in relation to magnitude of the zinc intake, the type of food consumed and the role of adaptive responses in maintaining adequate zinc nutriture. 

We conducted a human metabolic balance study to test the concept of dietary phytate/zinc molar ratio as a predictor of zinc bioavailability to humans. Using unaltered or enzymatically dephytinlzed wheat bran with ordinary foods we attained phytate zinc molar ratios of about 1 and 12 with relatively high intakes of dietary fiber in the menus and found no difference in zinc balance. Retrospectively, the result may be qualified on the basis of the magnitude of the zinc Intake and possible adaptive or homestatic responses over the period of the study. A second study was then conducted and a wider range of phytate/zinc molar ratio was provided than in the first study. We will briefly outline the first study, give a progress report on the second study and, with some information on phytate intakes obtained by our laboratory, discuss the nutritional implication. 

The molar ratio of phytate/zlnc of some mid-eastern diets was estimated to be 20 ( ), but only small amounts of meat were generally available. Sandstrom et al. obtained results that indicate absorption of zinc from a meal may be appreciably Influenced by the type of protein in the meal (, ). Our menus provided protein from meat in most of the meals which may have affected bioutilization of the dietary zinc. In one comparison Sandstrom et al. found that whole wheat bread decreased percentage absorption, but the absolute amount of zinc absorbed was greater because total zinc in the whole wheat bread meal was greater. 

Added and naturally-occurring phytates may affect zinc absorption differently although Morris and Ellis (13) report that phy-tate in wheat bran affects zinc utilization in rats in nearly the same manner as does phytate added at a similar phytate zinc molar ratio. One can arrive at a similar conclusion in examining the data in Table VI where cookie B containing added phytate compared well with cookie C which contained naturally-occurring phytate. 

In this study, [2-3H]MI or scyllo-[randomly positioned-3H]inositol ([R-3H]SI) was injected into hollow peduncles of post-anthesis developing wheat spikes. There was rapid translocation and accumulation of 3H in developing kernels. In the case of [2-3H]MI, 50-60% of the 3H from MI was found in cell wall polysaccharides that were recovered from the stem-region of the injection. That portion translocated to kernels was recovered in cell wall polysaccharides, phytate, galactinol, and MI. In the case of [R-3H]SI, most of the 3H was translocated to kernels where it accumulated as [R-3H]SI and O-a-galactosyl-SI. No 3H from [R-3H]SI was found in cell wall polysaccharides or phytate (Sasaki and Loewus, 1980). 

Table I. MBssbauer Spectrad Parameters of Wheat Seeds, Wheat bran, and Ferric Phytates ...

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