Dietary approaches aimed at combating vitamin A deficiency (VAD) through consumption of provitamin A carotenoids, in the form of biofortified foods, are becoming increasingly popular because of their assumed efficacy in addressing this challenge. This is on the premise that, regular consumption of biofortified staple foods, would contribute significantly to the vitamin A body stores of vitamin A deficient individuals. However, recent studies have demonstrated that content alone, cannot be relied upon completely as processing, food preparation and meal composition have been reported to have a greater effect on nutrient bioaccessibility and eventual delivery for intestinal absorption. In this study, the role of food processing and preparation (baking, boiling and composite meal preparation) methods in modulating the bioaccessibility and potential bioavailability of dietary carotenoids following simulated in vitro gastro-intestinal digestion was investigated. Test foods prepared from biofortified orange-fleshed sweet potato (OFSP) and maize foods, with varying degrees of caloric content, were subjected to both static and semi-dynamic digestions models for bioaccessibility and efficiency of micellarisation assessement. The resulting chyme was then exposed to differentiated Caco-2 cells and murine intestinal tissue to assess the potential bioavailability of dietary carotenoids using HPLC and LCS-MS analytical procedures. From the test foods analysed, processing led to a significant reduction in the contents of all the dietary carotenoids (P < 0.05) except for the β-carotene isomers, 13-cis-β-carotene and 9-cis-β-carotene. This is possibly due to trans-cis-isomerisation and potential degradation of the carotenoids. When different digestion models were compared, the efficiency of micellarisation, and therefore bioaccessibility for all-trans-β-carotene was significantly greater among the provitamin A carotenoids using the semi-dynamic (66.0 ± 2.0%) compared to the static method (58.0 ± 5.0%) (P < 0.05). Similarly, the micellarisation efficiency was greatest for lutein when assessed with the semi-dynamic method (75.3 ± 6.2%) compared to the static method (60.2 ± 7.1%) (P < 0.05). On the relationship between caloric density and bioaccessibility, addition of 5% vegetable oil to the OFSP (LIPID+OFSP) led to a two-fold increase in the bioaccessibility of both carotenoids (25 to 49%) for all-trans-β-carotene and 30 to 57% for β-cryptoxanthin. However, further addition of 5% protein (LIPID+OFSP+PROTEIN) led not only to an increase in the caloric density but also delayed delivery to the intestinal phase and thus reduction in the bioaccessibility in both carotenoids. Results of this study thus demonstrate how modification of food composition, through addition of moderate lipid and protein, in biofortified food material can improve the bioaccessibility and subsequent bioavailability of dietary carotenoids therefore reduce vitamin A deficiency in target populations. To validate these findings, carefully controlled human studies are needed using isotopic tracer methods to identify how meal composition modulates stability, digestion and bioavailability of dietary carotenoids in the body. This data can then be used by policy implementers to design and promote locally accepted meals, with the right energy composition, aimed at reducing the prevalence of vitamin A deficiency in afflicted populations.
