Bioavailable Grain Zinc in Bread Wheat Varieties of Pakistan.

Human zinc deficiency in developing countries like Pakistan is identified as a fifth major cause of diseases and deaths. In poor countries, the cost effective and sustainable approach to combat human zinc deficiency is enriching staple food grains with zinc. However, all the grain zinc is not available for human absorption due to certain antinutrients, major being phyate, in food. Trivariate model of zinc absorption in humans predicts the bioavailable zinc in food based on its phytate and zinc contents. In the present study, 51 bread wheat varieties, representative of local and foreign pool being used for genotype development, were sown at Wheat Research Institute, Faisalabad (Pakistan) during 2008–09. The main objectives of the study were: (i) to determine the variation in phytate and zinc concentrations in whole grains; (ii) to estimate the bioavailable zinc in grains by using trivariate model of zinc absorption; and (iii) to examine the interrelationship of bioavailable zinc with year of variety release. Average gain zinc in the varieties was 27.6 mg zinc kg-1 DW and ranged from 23.3 to 32.6 mg zinc kg-1 DW. Phytate in grains ranged from 7.2 to 11.0 mg g-1 DW resulting in a change in phytate:zinc molar ratio ranging from 25 to 44. However, there was a significant positive relationship (r = 0.32, n = 51) between the grain zinc and phytate concentrations. The bioavailable grain zinc ranged 1.52 to 2.05 mg zinc 300 g-1 wheat flour, indicating that only 19.2 to 24.5% of grain zinc is actually bioavailable. Bioavailable grain zinc significantly depended on the area of variety origin. Average bioavailable grain zinc in wheat varieties of Punjab province was lower than rest of the varieties from Pakistan. However, it was non-significantly higher than average of foreign wheat varieties. There was a significant negative correlation (r = -0.39, n = 32) between the grain zinc and year of variety release in Punjab province. Significant lower bioavailable grain zinc in currently cultivated varieties can be correlated to dilution effect due to higher yields. Therefore, an effective breeding program with optimized agronomic approaches is the urgent need for restoring and improving the bioavailable grain zinc in bread wheat for Pakistan.