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Phosphorus and Mineral Concentrations in Whole Grain and Milled Low Phytic Acid (lpa) 1-1 Rice

¹USDA-ARS, Dale Bumpers National Rice Research Center, P.O. Box 1090, Stuttgart, AR 72160. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 1-870-672-9300 (Ext. 227). Fax 1-870-673-7581. E-mail address: rbryant@spa.ars.usda.gov ³USDA-ARS, Small Grains and Potato Germplasm Research Facility, Aberdeen, ID 83210. ⁴Current address: BASF Corporation, Research Triangle Park, NC 27709.

Phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate) is the most abundant form of phosphorus (P) in cereal grains and is important to grain nutritional quality. In mature rice (Oryza sativa L.) grains, the bulk of phytic acid P is found in the germ and aleurone layer, deposited primarily as a mixed K/Mg salt. Phosphorus components and minerals were measured in whole grain produced by either the rice (Oryza sativa L.) cv. Kaybonnet (the nonmutant control) or the low phytic acid 1-1 (lpa1-1) mutant, and in these grains when milled to different degrees (10, 12, 17, 20, 22, and 25%, w/w). Phytic acid P is reduced by 42–45% in lpa1-1 whole grain as compared with Kaybonnet, but these whole grains had similar levels of total P, Ca, Fe, K, Mg, Mn, and Zn. In both genotypes, the concentration of phytic acid P, total P, Ca, Fe, K, Mg, and Mn in the milled products was reduced by 60–90%, as compared with whole grain. However, a trend was observed for higher (25–40%) total P, K, and Mg concentrations in lpa1-1 milled products as compared with Kaybonnet milled products. The reduction in whole grain phytic acid P in rice lpa1-1 is accompanied by a 5- to 10-fold increase in grain inorganic P, and this increase was observed in both whole grain and milled products. Phytic acid P was also reduced by 45% in bran obtained from lpa1-1 grain, and this was accompanied by a 10-fold increase in inorganic P. Milling had no apparent effect on Zn concentration. Therefore, while the block in the accumulation of phytic acid in lpa1-1 seed has little effect on whole grain total P and mineral concentration, it greatly alters the chemistry of these seed constituents, and to a lesser but detectable extent, alters their distribution between germ, central endosperm, and aleurone. These studies suggest that development of a low phytate rice might improve the nutritional quality of whole grain, milled rice and the bran produced during milling.