Phytic digestion

Several microbial species (in particular fungi) produce phytases (EC 3.1.3.8). The incorporation of suitable, microbially derived phytases in the diet can confer the ability to digest phytic acid on the recipient animals. This would have a threefold beneficial effect the anti-nutritional properties of phytic acid would be destroyed a lesser requirement for feed supplementation with inorganic phosphorous wottld exist and reduced phosphate levels would be present in the faeces. Several trials have confirmed that the inclusion of phytase in animal feed promotes at least some of these effects. However, the enzyme is not yet used in many cormtries. This may be explained, in part, by the fact that most microbial species only produce low levels of phytase activity which, obviously, has an effect on the cost of the finished product. It seems likely that widespread utilization of phytase within the industry will only be made possible by the production of this enzyme from recombinant sottrces, and at least two major enzyme companies are marketing such an enzyme for a nttmber of years now. 

Little agreement has been reached as to which dietary components or which food processes physiologially affect mineral availability. Many plant foods contain phytic acid, oxalic acid or other dietary fiber components that can be shown to chelate minerals. The effect of these dietary substances upon the final bioavailability of the mineral in question will depend upon the digestibility of the chelate (106). 

Phytic acid Widespread Cucurbita pepo 4- Starch digestion, sequesters... 

These associations may well form more tightly-bound complexes during the drying of the soy protein. The exclusion of water from the protein-phytic acid-zinc associations could lead to thermodynamically stable complexes that ate resistant to complete proteolytic digestion in the gastrointestinal tract. Short peptides or amino acid residues bound to zinc and phytic acid then would be poorly absorbed. For further discussion see Erdman et al. 

However, tamarind seeds have low levels of phytic acid comparable that of lima bean (Egbe and Akinyele, 1990, cited in 4)). Phytic acid decreases bioavailability of certain minerals and may interfere with the ntihzation of proteins dne to the formation of phytate-protein and phytate-mineial-protein complexes and also inhibits the digestive enzymes (Reddy et al, 1982, cited in 4)). The phytate conld, however, be snbstantially eliminated by processing methods snch as soaking and antoclaving (Reddy et al, 1982, cited in 4)). 

In conclusion, the insoluble fraction, which is by far the main part of cereal dietary fiber, does not bind measurable amounts of ash after digestion with proteolytic and amylolytic enzymes under conditions similar to those in the human gastrointestinal tract. All the binding capacity seems to be due to the small soluble fraction in which the polysaccharides but also most of the phytic acid is recovered. 

Xylanase is also used in animal feeds, along with several other enzymes to enhance digestibility and maximize nutritional and caloric yield, including man-nanase, alpha-galactosidase, and phytase. Phytase releases absorbable inorganic phosphate from phytic acid, one of the main storage forms of phosphorus in... 

The fact that phytic acid P is not completely available to the body, even in absence of calcium in the diet, was established by Lowe and Steenbock (1936). Increased Ca in the diet depresses phytic acid digestion considerably in the rat. Harrison and Mellanby (1939) observed that the mineralization of bones in puppies suffered as the result of the addition of phytic acid to the diet, and the explanation that phytic acid depresses the... 

Mellanby (1950), who also saw differences in phytic acid digestion in his puppies, discusses various possible explanations of the observed effect. One is that vitamin D should increase phytase secretion into the intestines. Another is that vitamin D acts on the phytic acid via calcium. 

To the authors of this review the second h3rpothesis offers a reasonable explanation of the effect observed. It is well known that, other conditions being equal, extra calcium in the diet depresses phytic acid digestion in man (Cruickshank et al., 1945), in rats (Lowe and Steenbock, 1936), and in puppies (Mellanby, 1949, 1950). In vitamin D deficiency the absorption of calcium is decreased. More calcium will be present in the intestinal content and will counteract the phytic acid digestion, partly by an inhibitory action on the phytase and partly by precipitating more phytic acid. 

A method of study suggests itself. Animals should be fed a diet free of calcium in the periods of exploration of phytic acid digestion. The rat, which has measurable quantities of phytase in the mucous membrane of the small intestine but in which the phytic acid digestion is still incomplete, is clearly the animal to be used. 

Sievwiight, C.A. Shipe, W.F. (1986). Effect of Storage Conditions and Chemical Treatments on Firmness, In Vitro Protein Digestibility, Condensed Tannins, Phytic Add And Divalent Cations of Cooked Black Beans (Phaseolus vulgaris). Journal of Food Science, Vol. 51, No.4, pp. 982-987. 

The addition of phytic acid to white flour markedly reduced the absorption of these minerals in short-term studies. With prolonged ingestion, the body can adapt to a high phytate intake apparently as a result of the action of enzymes which release the phosphate from soluble phytates. Phytases may be derived from the food, the digestive secretions or the intestinal bacteria. 

Controversy has been raging for many years as to whether, from the nutritional point of view, white or brown bread is better. Brown bread made from high extraction flour contains more protein, calcium, iron, B vitamins and fibre than white bread but its nutrients tend to be less well digested and absorbed. The case for white bread is based on its more attractive appearance, finer texture, better baking and keeping qualities and also its lower content of fibre and phytic acid which are responsible for the poorer utilization of nutrients. In Britain, where bread is only one of many articles of diet, nutritional differences between wholemeal and fortified white flours are of little practical significance. However, such differences could become important if bread ever became the single staple food. 

Jongbloed AW, Mroz Z, Kemme PA (1992) The effect of supplementary Aspergillus iger phytase in diets for pigs on concentration and apparent digestibility of dry matter, total phosphorus and phytic acid in different sections of the alimentary tract. J Anim Sci 70 1168... 

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