Bioaccessibility and tissue distribution of carotenoids and vitamin D from fortified foods
Novel approaches to food fortification are being developed in order to meet dietary gaps in micronutrient intake. The efficacy of food fortification relies on bioavailability of the nutrient, i.e. the nutrient must be released from the food matrix during digestion, absorbed at the intestinal epithelial surface, and delivered to target tissues for biological activity and/or storage. Underlying the investigation of bioavailability is the need for analytical methods to determine carotenoid and vitamin D concentrations in foods and tissues. The bioaccessibility and tissue distribution of carotenoids and vitamin D were investigated from three distinct food systems. Provitamin A carotenoid levels of sorghum are being enhanced through transgenic approaches in the Africa Biofortified Sorghum project, yet bioavailability of carotenoids has not been considered. Bioaccessibility of provitamin A carotenoids were assessed from 18 biofortified and wild-type sorghum varieties by in vitro digestion. The most promising biofortified variety was identified, and contained 4-8x more bioaccessible β-carotene equivalents than wild-type sorghum. Human breast milk is a primary source of bioactive carotenoids including lutein and zeaxanthin, which may protect the developing infant retina from light-induced damage. To develop additional insights into carotenoid profiles across lactation stage and country, human milk was analyzed from twenty donors in China, Mexico, and the USA at 2, 4, 13, and 26 weeks postpartum. Bioaccessibility and intestinal absorption of breast milk from 1-6 months postpartum and 9 prototypes of lutein-fortified infant formula were assessed by a coupled in vitro digestion/ Caco-2 human intestinal cell model. Bioaccessibility of lutein was not different between human milk (29±2%) and infant formula (36±4%), or between types of lutein-fortified formula. However, accumulation efficiency of lutein by Caco-2 from human milk was over 4x greater from human milk than infant formula and increasingly efficient at low levels of lutein. Sample preparation and LC-MS/MS methodology was developed in order to assess the tissue distribution of vitamin D and 25-hydroxyvitamin D from select soft tissues. 25-hydroxyvitamin D concentrations were ~1 ng/g from both vitamin D forms in muscle, liver, and adipose tissue. Total vitamin D concentration in adipose tissue reflected serum 25-hydroxyvitamin concentration, suggesting that potential differences in tissue accumulation did not cause the disparity in bioavailability. To isolate digestive processes from further metabolism, vitamin D bioaccessibility from fortified breads and bovine milks was assessed by in vitro digestion. Vitamin D bioaccessibility was lower from bread fortified with vitamin D2 enriched yeast than from crystalline vitamin D2 fortified breads and from bovine milks. Microscopy and solvent extraction of breads further suggests that vitamin D was not released from intact yeast cells. Together, these studies strongly indicate that increasing the carotenoid or vitamin D content of foods is not sufficient for effective fortification. Carotenoid and vitamin D bioaccessibility and absorption are a function of the food matrix these nutrients are placed into. Bioavailability is not only influenced by macronutrients such as lipid to aid in micellarization, but also the microenvironment that may physically trap or chemically associate with the nutrient, as well as biological factors that may potentiate intestinal absorption. While similar observations have been made before for other food systems, these data highlight the necessity of bioavailability assessment from any novel approach to fat-soluble micronutrient fortification. (Abstract shortened by UMI.)
Weaver, Purdue University.
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