Overview of the study

This study makes use of the stable isotope tracer technique.

1) Seeds from the biofortified strain of YM were first cultivated in deuterated heavy water (2H2O) so that the β-carotene produced will also be deuterated (2H-BC) - having deuterium atoms in them.

2) When subjects consume this maize, 2H-BC will be converted correspondingly into 2H-retinol in their bodies.
  
3) As 2H-retinol and 2H-BC are both heavier than their unlabelled counterparts, they can be traced and collected from the blood samples of the subjects.

4) Conversion factor is calculated by comparing the amount of 2H-BC consumed and the amount of 2H-retinol found in the blood.

Production of intrinsically-labelled yellow maize 

The biofortified strain of YM (DEexp × CI7) was grown hydroponically in a special nutrient solution containing minerals and deuterated heavy water (2H2O). After about 45 days, the matured maize ears were collected, dried and the maize kernels were removed.

Hydroponics is the technique of growing plants in mineral solutions instead of soil.

Production of intrinsically-labelled yellow maize dose 

In total, 874 g of the YM kernels were collected and ground into YM flour. About 145 g were used in High Performance Liquid Chromatography (HPLC) analysis to determine the concentration of the various carotenoids within (lutein, zeaxanthin, β-cryptoxanthin, β-carotene) before and after cooking. [Table 1 and Fig.2].

The remaining 729 g of YM flour  was cooked together with water into sadza, traditional Zimbabwean yellow maize thick porridge. Together, 2401 g of sadza was prepared.

Zimbabwean white maize sadza

Volunteers and study design

8 Zimbabwean men (mix of ethnicities) aged between 40 and 70, non-smoking and who have not been taking any Vitamin A or β-carotene supplements in the past month, volunteered to participate in the study.

The 8 men were instructed to abstain from Vitamin A or β-carotene rich foods for 2 weeks before the study. On day #1 of the study, 10mL of blood was drawn from each subject. They were then fed according to Table A. 

10mL of blood was then drawn 3,6,9,11 and 13 hours after the biofortified YM sadza dose and also on days #2,3,4,5,6 and 7. Everyday, low Vitamin A or β-carotene meals were offered to the subjects.

On day #8 of the study, 10mL of blood was again drawn from each subject. This time, the subjects were fed according to Table B.


10mL of blood was then drawn 3,6,9,11 and 13 hours after the 13C10 retinyl acetate dose and also on days #9, 10, 11, 13,15,19,22,29 and 36. Everyday, low Vitamin A or β-carotene meals were offered to the subjects.

Study design

***13C10 retinyl acetate served as a positive control for this study. Once in circulation,13C10 retinyl acetate would be converted to 13C10 retinol. If 13C10 retinol is found in the subjects' blood samples, this means that the body is indeed producing retinol normally, and that any 2H-retinol present would have been derived from 2H-BC itself. 

300g dose biofortified yellow maize sadza

20g butter

0.5g corn oil

= ~1.2mg β-carotene

Table A

300g dose white maize sadza

20g butter

1mg 13C10-retinyl acetate

0.5g corn oil

Table B