Evaluation of Zinc Bioavailability in Humans from Foliar Zinc Biofortified Wheat and from Intrinsic vs. Extrinsic Zn Labels in Biofortified Wheat

Abstract

Objectives: Zinc biofortification may be a sustainable way to improve Zn status, but questions remain on Zn bioavailability. We produced a novel biofortified wheat by Zn foliar application, and a separate wheat cultivar was intrinsically labeled with a Zn stable isotope. Goals were: a) To compare fractional and total Zn absorption (FAZ-TAZ) from chapattis prepared with biofortified, regular and postharvest fortified wheat; b) Compare the absorption of intrinsically and extrinsically Zn labels from biofortified wheat. Methods: Chapattis were prepared from flours with 100% and 80% extraction rates (ER). Meals were administered to 2 women's groups (N=44) in randomized order. Bioavailability was measured with double isotopic urinary technique with stable isotopes; four-day urines were collected and isotopic enrichment measured. Results: Foliar Zn application resulted in an increase of 45.6% of grain Zn. The control and biofortified wheat contained 25±0.12 ppm and 46±1.37 ppm Zn and 0.830±0.04 g/100 g and 0.807 ±0.03 g/100 g PA. The Zn:PA molar ratio for the unfortified, fortified and biofortified meals were 36, 63, 63 (100% ER) and 40, 67, 67 (80% ER). Mean total Zn in the intrinsically labeled wheat was 19.9±1.6 ppm. FAZ-TAZ data from the absorption studies are being analyzed. Conclusions: Foliar application increased Zn concentration without significantly changing PA concentration, and extraction rate is a determinant of the Zn:PA ratio. Assessment of FAZ-TAZ will provide: a) Data on the potential of foliar zinc biofortified wheat, and b) proof that the double isotope technique used to assess absorption of extrinsic Zn labels in biofortified wheat is valid.