Bioavailable Grain Zinc In Wheat Varieties Of Pakistan And Strategies For Biofortification

Wheat grains are an important source of minerals and calorie intake especially for human population living in the rural areas of developing countries.Under the widespread zinc (Zn) deficiency in soils and humans, biofortification of wheat grains grown on Zn deficient soils of Pakistan was hypothesized as a possible solution to human Zn deficiency.The research project comprised of six separate experiments focusing on four major issues: i) estimating Zn bioavailability in grains of wheat varieties of Pakistan; ii) evaluating the relationship of grain Zn concentration with soil Zn status; iii) optimizing rate and application methods of Zn to biofortify wheat grains; and iv) determining the effect of grain milling and flour extraction on Zn bioavailability. The bioavailability of Zn from the grains of selected wheat varieties was low as indicated by high phytate to Zn molar ratio ([phytate]:[Zn]) and low trivariate model of Zn absorption based estimated Zn bioavailability. Currently-cultivated varieties had higher grain yields and lower concentration and bioavailability of Zn than obsolete varieties of Punjab (Pakistan). Much of this variation was related to an increased grain weight in new varieties.Nutrient indexing of Zn in wheat crop and associated soils of cotton-wheat rotation zone of Punjab (Pakistan) indicated widespread soil Zn deficiency and a high risk of human Zn deficiency for the human population of the area. About 75% of surface and all the subsurface soil samples were deficient in plant available Zn resulting in a low grain Zn concentration (20�4 μg g−1). In another study, application of Zn significantly increased grain yield, grain Zn concentration and estimated Zn bioavailability while significantly decreased grain phytate concentration and [phytate]:[Zn] ratio in wheat grains.The levels of human requisite Zn concentration and estimated Zn bioavailability in wheat grains were estimated to be achieved at the soil Zn rates required for maximum grain yield (about 9 mg Zn kg−1 soil). Various Zn application methods, alone and in combinations, were evaluated in study 5.Soil Zn application increased grain yield up to 29%, grain Zn concentration up to 95% and estimated Zn bioavailability up to 74%. Foliar Zn application during grain development stage also greatly increased grain Zn concentration especially at lower soil Zn rates ( 50 μg g−1) and estimated Zn bioavailability (>3 mg Zn per 300 g flour) in wheat grains to levels generally desired for improved human nutrition.In the last study, Zn bioavailability from control and biofortified wheat grains was estimated in various grain milling fractions and flours of different extraction rates.Zinc and phytate concentrations and Zn bioavailability were significantly greater in bran compared to other grain milling fractions.There were severe losses in concentration and bioavailability of Zn from both control and biofortified wheat flour at lower flour extraction rates.Moreover, Zn bioavailability was remarkably higher in the biofortified wheat flour as compared to control and commercially available flours.Therefore, biofortified whole-grain flour was suggested for human consumption.As a whole, the project indentified the potential of wheat grown in Pakistan to supply optimum Zn for human nutrition by giving due importance to grain yield under optimum Zn application by suitable methods.