Yellow maize with high β-carotene is an effective source of vitamin A in healthy Zimbabwean men

Abstract

Background: The bioconversion efficiency of yellow maize β-carotene to retinol in humans is unknown.

Objective: The objective of this study was to determine the vitamin A value of yellow maize β-carotene in humans.

Design: High β-carotene-containing yellow maize was grown in a hydroponic medium with 23 atom% (2)H(2)O during grain development. Yellow maize β-carotene showed the highest abundance of enrichment as [(2)H(9)]β-carotene. Eight healthy Zimbabwean men volunteered for the study. On day 1 after a fasting blood draw, subjects consumed 300 g yellow maize porridge containing 1.2 mg β-carotene, 20 g butter, and a 0.5-g corn oil capsule. On day 8, fasting blood was drawn, and subjects consumed 1 mg [(13)C(10)]retinyl acetate in a 0.5-g corn oil capsule and 300 g white maize porridge with 20 g butter. Thirty-six blood samples were collected from each subject over 36 d. Concentrations and enrichments of retinol and β-carotene in labeled doses and serum were determined with the use of HPLC, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry.

Results: The area under the curve (AUC) of retinol from 1.2 mg yellow maize β-carotene was 72.9 nmol · d, and the AUC of retinol from 1 mg retinyl acetate (13)C(10) was 161.1 nmol · d. The conversion factor of yellow maize β-carotene to retinol by weight was 3.2 ± 1.5 to 1.

Conclusion: In 8 healthy Zimbabwean men, 300 g cooked yellow maize containing 1.2 mg β-carotene that was consumed with 20.5 g fat showed the same vitamin A activity as 0.38 mg retinol and provided 40-50% of the adult vitamin A Recommended Dietary Allowance. This trial was registered at clinicaltrials.gov as NCT00636038.

Figures

FIGURE 1.

Experimental design for the Zimbabwe yellow maize study. Three time scales are used to show the study design. The upper scale shows the entire 36-d study and sampling period. The middle scale shows days 1–15, a period of more frequent blood draws. Each cell on the middle and lower scales represents a 24-h period. On the middle scale the black cells represent days 1 and 8, which were the days on which labeled doses were administered. The lowest scale represents blood sampling time points on days 1 and 8, respectively. The 0 time shows the first blood draw of the day, and all the other numbers show the times of subsequent blood draws (h) relative to the time of the first draw. The anchor symbol shows the oral dosing of the labeled tracers. The arrows indicate the times at which blood samples were collected. d, day in time; h, hour after labeled dose or after fasting blood sample.

FIGURE 2.

C30 column HPLC chromatogram of high–β-carotene yellow maize line DEexp × CI7 − F1 (seeds from Torbert Rocheford of Purdue University,West Lafayette, IN). Peaks identified by arrows are lutein, zeaxanthin, β-cryptoxanthin, 13 cis-β-carotene, all-trans-β-carotene, and 9 cis-β-carotene. β-C, β-carotene; AU, arbitrary units.

FIGURE 3.

Deuterium enrichment profiles of high–β-carotene yellow maize line DEexp × CI7 − F1 by liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (positive ion mode) for June (A) and October 2006 (B) harvests. Hydroponic labeling produces a range of isotopomers. The most abundant isotopomer of labeled β-carotene with 9 deuterium atoms is represented by a mass-to-charge ratio (m/z) of 546 (M+H++2H9). The first arrow on each profile points to the 537 peak, showing that the molecular mass of unlabeled β-carotene is 537 (M+H+). The second arrow on each profile points to peak 546 (M+H++2H9), showing the highest abundance of enrichment.

FIGURE 4.

Chromatography and spectrum of labeled all-trans-β-carotene in serum of a representative subject 48 h after a yellow maize dose made from yellow maize line DEexp × CI7 − F1. A: The arrow points to the ultraviolet-visible spectrum of all-trans-β-carotene in the circulation, corresponding to the peak of all-trans-β-carotene in B. B: The HPLC chromatogram for the serum extract. C: The small arrow points to the 537 (M+H+) peak, showing the molecular mass of endogenous β-carotene, and the second, longer arrow shows the β-carotene enrichment peak at 546 (M+H++2H9) from the dose of yellow maize β-carotene that was absorbed as intact β-carotene into the serum (collected 2 d after the yellow maize dose and analyzed by liquid chromatography– mass spectrometry with atmospheric pressure chemical ionization and the use of a positive ion mode). mAU, mini absorbance unit.

FIGURE 5.

Calculated labeled retinol in the circulation of a representative volunteer during the study period after consumption of labeled yellow maize β-carotene on day 1 and a reference dose of [13C10]retinyl acetate on day 8. The continuous line and solid-circle data points show the serum [2H]retinol response of a subject after consumption of [2H]yellow maize β-carotene on day 1 of the study. The dashed line and solid-triangle data points show serum [13C10] retinol after consumption of a labeled reference dose of [13C10]retinyl acetate on day 8 of the study. The retinol in circulation measured in nanomoles is shown on the y axis, and time in days is shown on the x axis.