Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.Vitamin A deficiency (VAD) is a major public health problem in developing countries, including South Africa. The potential of provitamin A-biofortified maize for use as a complementary strategy to alleviate vitamin A deficiency in developing countries, where maize is the dominant staple food, is currently a subject of research. Although the nutritional composition of white maize is thought to be similar to that of biofortified maize, apart from the differences in provitamin A carotenoid content, the comparative nutritional composition of the two maize types seems not to have been subjected to a comprehensive scientific study. When setting the target level of provitamin A in the provitamin A-biofortified maize, it is important to consider the potential effect of processing on the final provitamin A carotenoid content of the biofortified food products, as the provitamin A carotenoids levels may decrease on processing. Furthermore, the yellow/orange provitamin A-biofortified maize may not be widely accepted by African consumers who are vulnerable to VAD, and are traditional consumers of white maize.
This study firstly aimed to evaluate the nutritional composition, including provitamin A composition, and grain quality of provitamin A-biofortified maize varieties, compared to white maize. The second aim was to assess the effect of processing (milling and cooking) on the retention of provitamin A carotenoids and other nutrients in popular South African maize food products prepared with provitamin A-biofortified maize. Thirdly, the study aimed to assess the acceptability of maize food products prepared with provitamin A-biofortified maize by consumers of different age and gender in rural KwaZulu-Natal, South Africa.
The grains of the provitamin A-biofortified maize varieties and grain of a white maize variety (control) were analysed for their nutritional composition using standard or referenced methods. The carotenoid content of the grains was analysed by High-Performance Liquid Chromatography (HPLC) and mass spectroscopy. The provitamin A carotenoids β-cryptoxanthin, and trans and cis isomers of β-carotene, and other unidentified cis isomers of β-carotene were detected in varying levels in the provitamin A-biofortified maize varieties. The total provitamin A content in the biofortified maize varieties ranged from 7.3-8.3 μg/g dry weight (DW), with total β-carotene ranging from 3.5-3.6 μg/g DW, and β-cryptoxanthin from 3.7-4.8 μg/g DW, whilst no carotenoids were detected in the white maize variety. Results of the evaluation of the content of other nutrients showed that, when compared with the white maize variety, the provitamin A-biofortified maize varieties had higher levels of starch, fat and protein but were lower in iron.
The zinc and phosphorus levels in the white maize and the biofortified maize were comparable. The biofortified maize varieties were better sources of most of the essential amino acids relative to the white maize, but, similar to the white maize, they were deficient in histidine and lysine, indicating that further improvement is required. Selected quality attributes (grain density, susceptibility of kernels to cracking, milling quality and resistance of the kernels to fungal infection) of grains of 32 provitamin A-biofortified maize varieties and a white variety (control) were assessed. Overall, the quality of the grains of the provitamin A-biofortified maize varieties were found to be superior to that of the white maize grain, although the biofortified maize grains showed less resistance to fungi, including mycotoxin-producing types. This indicates that the trait of grain resistance to infection by fungi should also be incorporated in the provitamin A-biofortified maize varieties during breeding.
To assess the retention of provitamin A carotenoids and other nutrients in maize food products, three selected provitamin A-biofortified maize varieties and the control (white maize variety) were milled into mealie meal and samp. The milled products were cooked into three products: phutu and thin porridge (from the mealie meal) and cooked samp. Nutrient retention during processing was determined. Milling resulted in either an increase or slight decrease in the provitamin A carotenoid levels, but there was no major decrease in the total provitamin A level. Most of the other nutrients were well retained during milling, but there were substantial losses of fibre, fat and minerals. Provitamin A carotenoid levels decreased on cooking. In phutu 96.6 ± 20.3% β-cryptoxanthin and 95.5 ± 13.6% of the β-carotene was retained after cooking. In thin porridge 65.8 ± 4.6% β-cryptoxanthin and 74.7 ± 3.0% β-carotene; and in samp 91.9 ± 12.0% β-cryptoxanthin and 100.1 ± 8.8% of the β-carotene was retained after cooking, respectively. Provitamin A retention seemed to be influenced by both maize variety and food form, indicating that suitable varieties and food forms should be found. There was generally a high retention of the other nutrients in all the three cooked products, except for the substantial losses of fat in thin porridge and iron and phosphorus in cooked samp. These findings indicate that an optimal delivery of provitamin A to the consumer can be achieved by processing provitamin A-biofortified maize into foods that have a good retention of provitamin A carotenoids, such as phutu and samp. These food products would be recommended in areas where VAD is prevalent.
In order to assess consumer acceptability of provitamin A-biofortified maize, a total of 212 subjects aged 3-55 years from Mkhambathini Municipality, in KwaZulu-Natal province, South Africa, participated in the sensory evaluation of phutu, thin porridge and cooked samp prepared with provitamin A-biofortified maize varieties and a white variety (control). Preference for yellow maize food products was negatively associated with an increase in the age of the subjects. Overall, preschool children preferred yellow maize to white maize food products: phutu (81% vs. 19%), thin porridge (75% vs. 25%) and samp (73% vs. 27%). In contrast, primary school children preferred white maize to yellow maize food products: phutu (55% vs. 45%), thin porridge (63% vs. 38%) and samp (52% vs. 48%). Similarly, secondary school children and adults also displayed a similar preference for white maize food products. There was no association between gender and preference for maize variety. Focus group discussions revealed that participants had a negative attitude towards biofortified maize due to its colour, taste, smell and texture. However, the participants expressed a willingness to consume biofortified maize if it was cheaper than white maize and was readily available in local grocery stores. These findings indicate that there is a potential to promote the consumption of provitamin A-biofortified maize and its food products in this part of South Africa, thereby contributing to a reduction in the incidence of VAD.
This study has shown that provitamin A-biofortified maize has a good potential to be used as an additional strategy to alleviate VAD in poor communities of South Africa, including similar environments in sub-Saharan Africa. However, the study has revealed that there are still challenges to be overcome in order to achieve the target provitamin A content of 15 μg/g in provitamin A-biofortified maize, set by HarvestPlus, an international challenge program. This may also explain why provitamin A-biofortified maize varieties with this level of provitamin A have been scarcely reported in the literature. Thus, more research is required to achieve the target provitamin A level in maize by conventional breeding. The results of this study indicate that besides provitamin A, the biofortified maize is also a good source of other nutrients including starch, fat, protein and zinc. However, improving the consumer acceptability of the provitamin A-biofortified maize remains a challenge, due to the negative attitudes towards the yellow/orange maize by African consumers. On the other hand, the results of this study indicate that there is an opportunity to promote the consumption of provitamin A-biofortified maize food products by preschool children, a finding which has not been previously reported in the literature. Nutrition education on the benefits of provitamin A-biofortified maize, as well as improved marketing are recommended, in this part of South Africa and also in similar environments in other sub-Saharan countries
