Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2007
Publication Date: May 7, 2007
Citation: Liu, K., Peterson, K.L., Raboy, V. 2007. Comparison of the Phosphorus and Mineral Concentrations in Bran and Abraded Kernel Fractions of a Normal Barley (Hordeum vulgare) Cultivar versus Four Low Phytic Acid (lpa) Isolines. Journal of Agricultural and Food Chemistry. 55:4453-4460. Interpretive Summary: Cereal grains form a significant portion of the food supply for humans and many other animals, as they are a major source of carbohydrates, proteins and lipids. A less widely recognized class of nutrients is the group of minerals, which has major nutritional significance for human and animals. Deficiencies in elements, such as Ca, Fe, Mn, Zn, can lead to a variety of medical problems from anemia to osteoporosis. One important factor affecting mineral bioavailability of grains for food and feed is the presence of phytic acid. It consists of 65-80% of the total phosphorus (P) in cereal grains, and interacts with certain minerals to reduce their availability to human and non-ruminant animals and contributes to increased P discharge into environments. Most phytic acid is stored as salts that are concentrated in the germ and aleurone layers. Although milling helps remove most phytic acid, the process also removes minerals and other nutrients concentrated in the bran fraction, thus reduce the nutritional value of the remaining kernel. One strategy to solve the problem is to develop crops that are lower in seed phytic acid content as compared with conventional cultivars. In this study, we compared the contents of various types of phosphorus and minerals in sequentially abraded bran fractions and corresponding kernels of four low phytic acid isolines having varying levels of phytic acid reduction with a normal barley cultivar, using a laboratory abrading method developed in out lab. This was to test our hypothesis that reducing the ability of grains to synthesize and accumulate phytic acid might alter both the amount and distribution of P and minerals in grain tissues. The significance of this study includes 1) it showed that there is no difference in mineral concentrations and distribution patterns between conventional barley variety and low phytic acid mutants. 2) It demonstrated that there is no direct role of localization of phytic acid synthesis in mineral distribution within a barley seed and that LPA breeding does not lead to reduction in mineral contents in barley seeds. 3) It helped clarify controversy on the subject within scientific community and provided direct evidence to justify LPA breeding programs.
Technical Abstract: Phytic acid consists of 65-80% of the total phosphorus (P) in cereal grains. Its salts are concentrated in the germ and aleurone layers, which are typically removed during milling. We hypothesize that concentrations of different types of P and minerals in milled products will be greatly altered in low phytic acid (lpa) barleys. Seeds of cv. Harrington (Control) and 4 lpa isolines, lpa1-1, 1pa2-1, lpa3-1, and M955, were abraded by a laboratory method into 5 surface layer and 4 remaining kernel fractions. Results show that phytic acid in the 4 lpa lines ranged from 75% to 5% of the Control. The decrease in phytic acid P concentration was matched almost equally by an increase in inorganic P, so that the rest of P (the sum of all P-containing compounds other than phytic acid P and inorganic P) and total P levels remained relatively unchanged among the five genotypes. These trends were also observed for the processed fractions. The major mineral elements in barley seeds were P, K, Mg, S, and Ca, while minor ones were Fe, Zn, Mn, Cu, and Ba. All types of P and other minerals measured were generally concentrated in the outer layers of the grain. Although there were substantial differences in mineral contents of bran fractions among genotypes, the level of phytic acid P had little effect on mineral contents in whole or abraded kernels. One major exception was Fe, which had the highest level in all tissues of M955 genotype. The above findings were all confirmed by analyzing another set of barley samples grown in a different environment. Thus, in general, breeding lpa barleys does not lead to reduced mineral contents in whole grains or elevated mineral levels in milled products.