Phytic acid soybean

Minor Constituents. All four oilseeds contain minor constituents that affect the use of the defatted seeds, especially in feeds and foods. Percentages of phytic acid [83-86-3] (3), for example, are soybean, 1.0—1.5 (30) cottonseed kernels, 2.2—3.8 (25) peanut kernels, 0.8 (25) and sunflower, 1.6-1.7 (31). 

Contamination of soybeans with Aspergillus flavus is found in approximately 50% of commercial samples. Fortunately, the incidence of aflatoxin from this route is quite low. Moisture at [he time of maturity, development of the seed in a closed pod, and binding of zinc by phytic acid are suggested as reasons for resistance of soybeans to aflatoxin production... 

Soybean meal is generally low in minerals and vitamins (except choline and folic acid). About two-thirds of the P in soybeans is bound as phytate and is mostly unavailable to animals. This compound also chelates mineral elements including Ca, magnesium, potassium, iron and zinc, rendering them unavailable to poultry. Therefore, it is important that diets based on soybean meal contain adequate amounts of these trace minerals. Another approach to the phytate problem is to add phytase, a phytic acid degrading enzyme, to the feed to release phytin-bound P. A benefit of this approach is that less P needs to be added to the diet, reducing excess P loading into the environment. 

The ash content of soybeans is relatively high, close to 5 percent. The ash and major mineral levels in soybeans are listed in Table 5-7. Potassium and phosphorus are the elements present in greatest abundance. About 70 to 80 percent of the phosphorus in soybeans is present in the form of phytic acid, the phosphoric acid ester of inositol (Figure 5-5). Phytin is the calcium-magnesium-potassium salt of inositol hexaphosphoric acid or phytic acid. The phytates are important because of their effect on protein solubility and because they may interfere with absorption of calcium from the diet. Phytic acid is present in many foods of plant origin. 

Phytate. Phytic acid is an organic polyphosphate found widely in plants, particularly cereals, nuts and legumes. It has been shown to complex with various divalent cations in the gastrointestinal tract and thus reduce mineral bioavailability (33,44,52). Davis et al. (53) reported that feeding a diet based on isolated soybean... 

Hegeman, C.E., Good, L.L., and Grabau, E.A., 2001, Expression of D-myoinositol-3-phosphate synthase in soybean. Implications for phytic acid biosynthesis. Plant Physiol. 125 1941-1948. 

Hitz, W.D., Carlson, T.J., Kerr, P.S., and Sebastian, S.A., 2002, Biochemical and molecular characterization of a mutation that confers a decreased raffinose saccharide and phytic acid phenotype on soybean seeds. Plant Physiol. 128 650-660. 

Both the glycolipids and the phospholipids of corn have lower percentages of linolenic acid (18 3) and are more saturated than those in the soybean. In general, cmde corn and soybean lecithins are equal in linoleic acid (18 2) content, but lino-leic acid in corn varies from 42% to 70% depending on the variety of corn. Phytic acid, 88% of which is in the com germ, is extracted as part of the lecithin fraction (32, 37). Elimination of phytic acid in com is desirable because it binds zinc, magnesium, and calcium. 

Considerable research has identified several potential health benefits associated with increased soy consumption, and soybeans, which contain trypsin inhibitors such as phytic acid, saponins, and phytoestrogens, are now looked upon for potential health benefits. 

Phytate is the calcium, magnesium or potassium salt of phytic acid, which is inositol hexaphosphoric acid (Fig. 10.9). More than half of the total phosphorus in soybeans is in the form of phytic acid (Liu, 2004a). Because of its chelating power, phytic acid makes many essential minerals in soybeans or in diets unavailable for absorption and utilization for both human and domestic animals thus phytic acid is known as an anti-nutritional factor. 

Anderson, R.L. WJ. Wolf. Compositional changes in trypsin inhibitors, phytic acid, saponins, and isoflavones related to soybean processing,/. Nutr. 1995, 125, 581S—588S. 

Lolas, G.M. N. Palamidas P. Markakis. The phytic acid—Total phosphorus relationship in barley, oats, soybeans and wheats. Cereal Chem. 1976, 53, 867-871. 

Toda, K. K. Takahashi T. One K. Kitamura Y. Nakamura. Variation in the phytic acid content of soybeans and its effect on consistency of tofii made from soybean varieties with high protein content. / Sci. FoodAgric. 2006, 86, 212—219. 

Although A. flavus will grow on almost any natural or processed substrate, aflatoxin occurs naturally primarily in corn, peanuts, cottonseed, grain sorghum, tree nuts, millet, copra, and figs (34). Substrate factors must be involved in contamination, since it is limited to a relatively small number of agricultural commodities. The restricted access of zinc has been proposed as an explanation for the inability of A. flavus to elaborate aflatoxin in soybeans (35). The availability of zinc for aflatoxin biosynthesis appears to be blocked by the presence of phytic acid in soybeans (36). 

Phytic Acid. Recent reviews (67,68,69) summarized the literature covering the relationship between phytic acid and mineral bioavailability in soy protein products. The formation of phytate-proteln-mineral complexes (particularly zinc chelates in flours, concentrates, and Isolates prepared from mature soybeans) may be responsible for reduced mineral availability. However, the iron in Fe-labeled mature soybeans is more available to iron-deficient rats than the iron in green-immature soybeans, even though mature soybeans contain three times more phytic acid (70). The factor(s) responsible for this difference in bioavallablllty has not been identified. 

Seed germination decreases phytate and Increases phytase activity (Table X). A 22% decrease in phytic acid occurs during 5 days of soybean germination (62). Phytase activity in soybeans Increased 227% compared to an Increase of 907-3756% in peas. 

Zhou JR, Fordyce CJ, Raboy V, et al. 1992. Reduction of phytic acid in soybean products improves zinc bioavailability in rats. J Nutr 122(12) 2466-2473. 

Phytic acid and camosine (histidine-containing dipeptide), obtained from cereal and meat by-products, are effective inhibitors of hpid oxidation by several mechanisms, including metal inactivation and free radical quenching. Uric acid obtained from the decomposition of adenosine triphosphate in muscle also inhibits lipid oxidation by the same mechanisms. However, the importance of uric acid as an endogenous antioxidant in muscle foods is not clear. Various protein concentrates from soybeans, cottonseed and peanuts inhibit hpid oxidation in muscle foods. In addition to their iron binding activity, these crade extracts contain complex polyphenolic flavonoids that have potent antioxidant activity. 

Additional detail concerning the composition of the egg white biotin-fortified diet and the method for analysis of the zinc content of the diets is supplied in a recent publication by Leucke and Fraker (1979). Diets containing phytic acid or soybean protein contaminated with phytic acid should be avoided since the amount of zinc available for absorption is unknown and phytic acid can chelate metals other than zinc. 

---