The Role of Antioxidants in Enhancing the Vitamin A Value of Plant Foods in Child Nutrition.
Abstract: Vitamin A
deficiency is a public health problem among children aged 6-36 months old in Zimbabwe.
The children are vitamin A deficient partly because the complementary diets are starchy
white gruels, devoid of vitamin A or provitamin A carotenoids. Green leafy vegetables of
Brassica oleracea family such as kale are rich in provitamin A carotenoids. Despite the
widespread consumption ... read moreof kale, it is not a common complementary food. A kale
complementary food cooked with peanut butter is not only nutrient and energy dense, but
may also increase the bioavailability of &beta-carotene. Kale is consumed as relish
to staple maize porridge. Therefore, it is important to also optimize the vitamin A
value of maize based complementary foods. Our previous studies show that
&alpha-tocopherol, an antioxidant found abundantly in maize promotes the exclusive
central cleavage of &beta-carotene by the BCMO1 enzyme to vitamin A. However, the
genetic variation of vitamin E and antioxidants in biofortified yellow maize and their
effects on BCMO1 enzyme is unknown. Currently, there is also a lack of information on
the genetic characterization of carotenoids in Brassica oleracea green vegetables
consumed in Zimbabwe, and human studies showing their vitamin A value. The primary
objective of this thesis was to demonstrate that kale and biofortified maize can improve
the vitamin A value of complementary foods in Zimbabwe. The following studies were
pursued to address the primary objective. The first study determined the genetic
variation of carotenoids, vitamin E and phenolic compounds in biofortified maize. HPLC
analysis of 20 genotypes of biofortified maize showed &beta-cryptoxanthin and
&beta-carotene as the main provitamin A carotenoids. Biofortified maize was also
high in vitamin E, γ-oryzanol, ferulic acid and p-coumaric acid. Our study showed
that genotype was a significant determinant of provitamin A carotenoids and vitamin E
variation in maize (p<0.01). The second study characterized carotenoid profiles of
brassica oleracea var. acephala vegetables varieties commonly consumed in Zimbabwe. HPLC
analysis showed significant differences in the lutein and &beta-carotene contents
among the six brassica oleracea vegetables varieties (p<0.05). Our study showed that
the Zimbabwean brassica oleracea var. acephala vegetables are a very good source of
provitamin A carotenoids. Our third study determined the effect of antioxidants on the
enzymatic cleavage of &beta-carotene in vitro. Extracts of kale and biofortified
maize were incubated with rat intestinal mucosal homogenate for an hour at 37°C.
This study showed that vitamin E and γ-oryzanol promote central cleavage of
&beta-carotene to form vitamin A. The fourth study determined the effect of peanut
butter on the bioconversion of deuterium labeled kale [2H9] &beta-carotene to
vitamin A. Preschool children were randomly assigned to ingest 1 mg [13C10] retinyl
acetate reference dose and 50 g cooked kale (1.5 mg &beta-carotene) with either 33 g
peanut butter (PBG) or 16 g lard (LG) on d1. Serum samples were analyzed by NCI-GC/MS
for the enrichments of labeled [2H] retinol from kale [2H9] &beta-carotene and
[13C10] retinol from reference dose. The area under the curve (AUCs) of molar retinol
enrichments at days 1, 2, 3, 6, 15, and 21 after the labeled doses showed the calculated
conversion factors of kale &beta-carotene to vitamin A to be 13.4 ± 3.1 and
11.0 ± 3.9 to 1 by weight for LG and PBG respectively. This showed that kale is a
good source of vitamin A. In summary, our research studies showed that kale and
biofortified maize can improve the vitamin A value of complementary diets of children
aged 6-59 months who are vulnerable to vitamin A
Thesis (Ph.D.)--Tufts University, 2014.
Submitted to the Dept. of Biochemical and Molecular Nutrition.
Advisor: Guangwen Tang.
Committee: Odilia Bermudez, Kyung-Jin Yeum, and Andrew Siwela.
Keywords: Nutrition, Chemistry, and Food science.read less
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