Trait Stacking Simultaneously Enhances Mineral and Provitamin a Carotenoid Bioaccessibility in Biofortified Sorghum bicolor

OBJECTIVES: Vitamin A, iron, and zinc deficiencies represent major dietary inadequacies in Sub-Saharan Africa and disproportionately affect women and children. Biotechnology strategies have been tested to individually improve carotenoid or mineral content and/or bioaccessibility in relevant cereal crops such as sorghum (Sorghum bicolor). However, approaches combining carotenoid and mineral enhancement in the same event have not been thoroughly evaluated. This work evaluated genetically engineered sorghum events that simultaneously enhanced provitamin A carotenoid accumulation and reduced the mineral limiting antinutrient phytate. METHODS: Two sorghum transformation constructs containing HGGT, to increase vitamin E accumulation and stabilize provitamin A carotenoids during grain storage, CRTI, to increase provitamin A biosynthesis, PSY1 or CRTB, to increase flux through the carotenoid pathway, and PhyA, to decrease phytate, were engineered to produce transgenic events. These sorghum events were processed into model porridges and evaluated for carotenoid and mineral content as well as bioaccessibility. RESULTS: All transgenic events produced markedly higher amounts of carotenoids compared to corresponding null segregants and wild-type control (Tx430). A steeping step prior to porridge production to pre-activate phytase drastically reduced phytate content, altered the profile of inositol phosphate conversion products, and reduced molar ratios of phytate to iron and zinc; preventing the chelation of minerals by phytate and enhancing their bioaccessibility. The subsequent release of minerals did not affect micellarization efficiency and the bioaccessible fraction of provitamin A carotenoids were over 2300% greater in transgenic events compared to corresponding null segregants and wild-type controls; providing 53.7% of a 4–8-year-old child's vitamin A estimated average requirement in a standard 200 g serving of porridge. CONCLUSIONS: These data suggest that a combination of strategies to enhance micronutrient content and bioaccessibility are feasible and warrant further assessment in human studies. FUNDING SOURCES: This work was supported in part by the U.S. Department of Agriculture, Agricultural Research Service as well as the Bill and Melinda Gates Foundation.