Effect of phytate level in whole wheat flour on mineral bioavailability in rats
Abstract
The bioavailability of calcium (Ca), iron (Fe), zinc (Zn) and selenium (Se) from whole wheat flour containing varying levels of phytic acid was determined in rats. Wheat was grown hydroponically in nutrient solution containing 6 and 31 ppm phosphorus (P) to produce varying levels of phytic acid in the kernel. The wheat was intrinsically labeled with $\sp{45}$Ca, $\sp{59}$Fe, $\sp{65}$Zn and $\sp{75}$Se by stem injection during growth. The relative order of efficiency of isotope incorporation into grain was $\sp{65}$Zn (57.65%) $>\ \sp{75}$Se (37.55%) $>\ \sp{59}$Fe (27.26%) $>\ \sp{45}$Ca (8.53%). Intrinsically labeled whole wheat flour containing low (0.08%), intermediate (0.67%), medium (1.64%) or high (1.83%) levels of phytate was added to test meals and fed to groups of ten male Sprague Dawley rats. There was no significant difference in $\sp{45}$Ca absorption in rats consuming the low or medium phytate test meals, as determined by femur $\sp{45}$Ca retention. However, rats consuming the high levels of phytate showed about 8% less absorption of $\sp{45}$Ca. Bioavailability of Fe, Zn and Se was determined by whole-body retention of $\sp{59}$Fe, $\sp{65}$Zn and $\sp{75}$Se. The decrease in iron absorption among treatment groups by increasing levels of endogenous phytate was statistically significant. Increasing concentration of phytate in whole wheat flour had a significant effect on zinc absorption. The bioavailability of $\sp{65}$Zn to rats from intermediate (91.55 $\pm$ 3.0), medium (89.36 $\pm$ 1.7) and high (88.91 $\pm$ 1.6) phytate wheat flour was significantly lower than that from low (94.55 $\pm$ 1.8) phytate flour. However, there was no significant difference in $\sp{65}$Zn absorption between groups consuming medium and high phytate flour. Absorption of $\sp{75}$Se in rats from medium (81.52 $\pm$ 2.0) and high (81.08 $\pm$ 1.8) phytate wheat flour was significantly lower than that from low (84.49 $\pm$ 1.8) phytate flour. Groups fed medium and high phytate flour showed no significant difference in $\sp{75}$Se absorption. In conclusion, bioavailability of Fe, Zn, Ca and Se was decreased by increasing the endogenous phytate from intrinsically labeled whole wheat flour. The extent of inhibitory effects of phytate on the mineral bioavailability depends on the amount of total phytate present in diet and type of mineral. Absorption of Ca, Fe, Zn and Se from whole wheat flour is very high regardless of the phytate concentration in the flour in the rat model, due to the low mineral density in wheat compared to animal derived food products. (Abstract shortened by UMI.)
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition|Livestock
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