Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/14/2011
Publication Date: 3/21/2011
Citation: Lonnerdal, B., Mendoza, C., Brown, K., Rutger, J.N., Raboy, V. 2011. Zinc absorption from low phytic acid genotypes of maize (Zea mays L.), barley (Hordeum vulgare L.) and rice (Oryza sativa L.) assessed in a suckling rat pup model. Journal of Agricultural and Food Chemistry. 59:4755-4762. Interpretive Summary: Seed-derived dietary phytic acid can contribute to zinc deficiency in human populations that rely on cereals and legumes as their primary foods. One possible approach to enhancing zinc nutrition would be to breed crops with reduced phytic acid. A relatively rapid method to test for the nutritional availability of zinc in foods is to use suckling rat pups as experimental models. Rat pups were fed diets prepared using lines of maize, barley and rice that have normal levels of phytic acid, and lines of each species with phytic acid levels genetically reduced by 50% to 90%. All low phytic acid lines had levels of zinc similar to their normal control lines. Zinc absorption was 30% to 50% higher in rat pups that consumed low phytic acid cereals as compared with pups consuming normal phytic acid grains. This illustrates the potential of low phytic acid cereal grains in enhancing mineral nutritional health of populations that rely on cereals and legumes as staple foods. This study also represents the first nutritional evaluation of a low phytic acid rice.
Technical Abstract: Phytic acid (PA) is an inhibitor of zinc (Zn) absorption. Because dietary PA is a major causative factor for low Zn bioavailability from most diets, a reduction in the PA content of staple diets is likely to improve Zn nutrition in populations of risk of Zn deficiency. Reducing the PA content of maize, barley and rice by selecting and breeding low PA (lpa) seed genotypes might increase Zn absorption. Suckling rat pups (14 days old, n=6-8/treatment) were fasted for 6 h and intubated with suspensions of maize, barley or rice radiolabeled with 65Zn. Several genotypes of each cereal containing reduced PA concentrations were tested. Test solutions were prepared and radiolabeled overnight (all genotypes) or immediately prior to intubation (barley genotypes). Pups were killed 6 h post-intubation, tissues removed and counted in a gamma counter. Zn absorption was low from wild-type (WT) genotypes of maize (21%, 33%) and rice (26%), and PA reduction resulted in significantly higher Zn absorption, 47-52 % and 35-52%, respectively. When the WT barley solutions were prepared immediately before intubation, Zn absorption was significantly lower (63%, 78%) than from the lpa cultivars (92 %, 96 %). Zn absorption from WT barley incubated overnight was high (86-91 %) and phytate reduction did not improve Zn absorption (84-90 %), which is likely due to endogenous phytase activity. These results in indicate that reducing the PA content of maize, barley and rice enhanced Zn absorption and is likely to improve Zn nutrition of populations consuming these staple foods. Endogenous phytase activity of some cereals needs to be taken into account when designing experiments evaluating Zn bioavailability, but can also be utilized to improve Zn absorption from such cereals.