Yellow Maize with High Beta-Carotene Is An Effective Source of Vitamin A.

Maize is an important staple food crop that is grown throughout much of the developing world; this includes regions of Africa, where vitamin A malnutrition is prevalent. Maize does not typically contain high levels of pro-vitamin A carotenoids, such as β-carotene, but varieties containing high levels of this carotenoid are currently being developed by breeders.  In order to determine the vitamin A value (i.e., β-carotene conversion efficiency) of yellow maize directly in humans, a selected high β-carotene-containing maize line was intrinsically labeled with deuterium (a non-radioactive stable isotope of hydrogen), by growing plants in a nutrient solution containing 23% heavy water (deuterium oxide). The maize β-carotene was enriched with deuterium with the highest abundance isotopomer peak at M+9.  Eight healthy Zimbabwean men with a mean serum retinol concentration of 59.2 ± 17.l ug/dL, and mean body mass index (in kg/m²) of 22.4 ± 3.1 volunteered for the study. On day 1 after a fasting blood draw, subjects consumed 300 g of yellow maize porridge containing 1 mg β-carotene, 20 g of butter, and a 0.5 g oil capsule. On day 8, after a fasting blood was drawn, subjects consumed 1 mg [¹³C₁₀] retinyl acetate in oil capsule and 300 g of white maize porridge with 20 g of butter. Thirty-six blood samples were collected from each subject over 36 days. Concentrations and enrichments of retinol and β-carotene in dose and serum were determined using HPLC, GC/MS and LC/MS. By using the response to the dose of ¹³C-retinyl acetate as reference, the conversion efficiency of 1 mg yellow maize β-carotene was 3.7 ± 1.0 to 1 (mean ± SD) by weight. Thus, in eight healthy Zimbabwean men, 1 mg yellow maize β-carotene consumed with 20 g butter and 0.5 g oil capsule was shown to have the same vitamin A activity as 0.37 mg retinol. Results of these studies will be presented in the context of yellow maize's potential contribution to population-based vitamin A adequacy. This work was supported by funding from Nutricia Research Foundation, Netherlands, Pioneer Hi-Bred International, USA, and USDA-ARS through Coop. Agrs. 58-1950-9-001, 58-6250-0-008, and 58-1950-7-707.