Biofortification is a process that improves the nutrient content of crops through plant breeding or recombinant DNA technology (rDNA) [1
]. Biofortified crops could play a vital role in improving the nutritional status of vulnerable population groups, where supplementation, conventional fortification, or dietary diversity are limited or problematic to implement [1
]. HarvestPlus, a global Challenge Programme, aims to reduce micronutrient malnutrition by developing crops that are higher in vitamin A, iron, and zinc, and have selected seven crops for biofortification, namely: beans (Phaseolus vulgaris)
, maize (Zea mays
), pearl millet (Pennisetum glaucum
), wheat (Triticum aestivum)
, cassava (Manihot esculenta
), sweet potato (Ipomoea batatas
), and rice (Oryza sativa
). Of these crops, cassava, maize, and sweet potato have been selected for provitamin A (PVA)-biofortification [1
]. The current PVA breeding targets for maize and sweet potato are 15 µg/g and 32 µg/g, respectively [3
]. White maize and cream-fleshed sweet potato (CFSP) are two commonly grown and consumed food items in South Africa [5
], and, therefore, are ideal for PVA-biofortification [5
]. The two crops are deficient in PVA carotenoids, the precursors of vitamin A found in plants [6
]. This could partly explain the slow improvement in the vitamin A status of the South African population, especially children [8
Vitamin A is an essential micronutrient that has several physiological roles including immunity, vision, and protein synthesis [9
]. In South Africa, between 1994 and 2005, the number of children with vitamin A deficiency (VAD) increased from 33.3% to 63.6% [10
]. Although, the results from the SANHANES-1 study of 2012 showed a decrease in VAD prevalence, the prevalence of VAD is still high (43.6%) [8
]. Biofortification could be used as a complementary strategy to reduce VAD in vulnerable population groups. However, PVA-biofortified foods, especially maize, have been found less acceptable compared to their non-PVA-biofortified counterparts [12
]. This has been attributed to the unfamiliar sensory attributes imparted by carotenoid pigments present in PVA-biofortified foods [12
]. Consumer acceptability of PVA-biofortified foods could be improved by combining them with other commonly consumed food items (plant or animal food sources) as they could mask the undesirable sensory properties of the PVA-biofortified foods. The only published study that investigated the acceptance of combining PVA-biofortified foods reported improvement in consumer acceptability of PVA-maize porridge when it was combined with chicken stew [17
]. Unlike biofortified maize, orange-fleshed sweet potato (OFSP) is well accepted by consumers [18
], and, therefore, there are fewer challenges of consumer acceptability of foods containing OFSP.
Apart from increasing the PVA content of popular vitamin A-deficient traditional and indigenous plant-based dishes of KwaZulu-Natal (KZN), PVA-biofortified maize and OFSP are also likely to affect the concentration of other nutrients in the dishes. The study objective was to determine the effect of replacing white maize and CFSP with PVA-biofortified maize and OFSP on the nutritional composition of traditional dishes of KZN province of South Africa. Traditional dishes are food types that, over a long time, have been associated with specific population group/s residing in a defined geographic location, and consumption of the dishes is passed down through generations [23
]. The food types studied were phutu
(crumbly maize porridge) prepared with white maize meal and PVA-biofortified maize meal, served with either curried chicken, curried cabbage, or curried bambara groundnut, and, separately, boiled sweet potato (CFSP and OFSP).
Globally, about two billion people experience micronutrient deficiency, mainly because their diets are of very limited diversity [35
]. Undernutrition, particularly protein-energy malnutrition and micronutrient deficiencies, is more prevalent in developing regions, especially sub-Saharan Africa, where a significant proportion of the population groups are poor and food insecure [11
]. The poor communities cannot afford a nutritious, diversified diet; they rely heavily on monotonous diets of starchy staples, which are generally low in essential nutrients, including micronutrients and protein [38
]. Among the micronutrient deficiencies, VAD as well as iron and zinc deficiencies, are generally leading [41
]. This emphasises the need to provide an affordable alternative source of essential nutrients, such as vitamin A, zinc, iron, and protein. Biofortified staple crops, which are being developed such that they contain much higher concentrations of target nutrients, like vitamins and minerals, compared to the corresponding non-biofortified crops, if consumed regularly, would result in significant improvements in human health and nutrition [42
As is the case with most of the countries in the sub-Saharan African region, micronutrient deficiencies, especially VAD, are a significant problem in South Africa [8
]. The KZN province has the largest proportion of poor households in South Africa, and has been one of the poorest provinces in South Africa since 2011 [43
]. Many of these impoverished communities are unable to purchase foods that form a diversified diet, and end up consuming mainly starch-based food [36
]. A basic food basket comprising 28 items in South Africa costs about US$
50, which is unaffordable to most rural population groups [45
]. Poor households are at a high risk of malnutrition, as they cannot afford a diversified diet [46
]. Increasing the concentration of provitamin A in staple crops through biofortification is a promising strategy for contribution to combating VAD. The results of this study are encouraging, as they indicate that PVA-biofortified maize contained a much higher PVA carotenoid concentration compared to white maize (control), which is consistent with previous studies [48
It appears that, currently, there are no published data on the nutritional composition of composite dishes containing PVA-biofortified maize food products like phutu
. However, when either cabbage curry, chicken curry, or bambara groundnut curry were combined with PVA maize phutu
, the PVA carotenoid concentration of the composite dishes was higher than that of the corresponding composite dishes containing white maize (controls). The results indicate that composite dishes in which PVA-biofortified maize phutu
is combined with other commonly consumed food items would be suitable carriers of provitamin A for delivery to the target population groups, such as the poor, rural communities of KZN. In the current study, bambara groundnut was included in the dishes containing maize, because it could be used as an affordable protein source, which has the added advantage of thriving in the predominantly harsh agro-ecological conditions of most of the marginal rural areas of sub-Saharan African countries, including the rural areas of KZN [49
]. Previous consumer acceptability studies conducted on bambara groundnut showed promising results, but the studies investigated bambara groundnut food types different from that of the current study [50
]. In terms of nutritional composition, the composite dish consisting of PVA-biofortified phutu
and bambara groundnut curry shows a potential for improving the vitamin A and protein status of vulnerable population groups, but the acceptability of such dishes to the target population groups should be investigated, because bambara groundnut is not a familiar food item to the majority of South Africans [53
While it is important to note that PVA carotenoids must be converted into vitamin A, which then can be used by the human body [54
], a study conducted by Palmer et al. found that there were improved serum β-carotene levels in Zambian pre-school children that routinely consumed dishes prepared with biofortified maize [55
]. Other studies have found that the consumption of biofortified maize resulted in an effective conversion of PVA into vitamin A [56
]. These results reinforce the hypothesis that PVA biofortified maize could be used as a sustainable and effective complementary strategy to address VAD.
The PVA carotenoid concentration of OFSP was much higher than that of the CFSP, which, as expected, had a nutritionally insignificant PVA concentration. Regarding CFSP, the PVA values obtained in the current study agree with values reported in the literature [58
]. The high PVA carotenoid concentration of OFSP could contribute to reducing VAD in vulnerable population groups. Another strategy that could be investigated is combining OFSP with other commonly consumed food item/s to enhance the nutrient content of the dishes, including provitamin A as well as other micronutrients with a high prevalence of deficiency. However, this study did not investigate the nutritional composition of composite dishes in which the OFSP was combined with other commonly consumed food items, and, therefore, further investigations are required.
As stated earlier, mineral deficiencies, especially iron and zinc deficiencies, are a serious health problem in sub-Saharan African countries, including South Africa, but, unfortunately, they are often unnoticed and are not routinely treated. In the current study, the total mineral content (ash) of the individual curries (bambara groundnut, chicken, and cabbage curry, separately) was higher than that of PVA-biofortified phutu
, which implies that the mineral content would be increased if either of the three curries were combined with PVA maize phutu.
Yet again, chicken curry was the best option to improve the mineral content. Biofortified crops, if consumed in the correct quantities, could improve the micronutrient status of the affected communities [59
]. Unlike a study conducted by Pillay et al. which found that the concentration of iron lower in PVA-biofortified maize than the white maize [60
], the current study found no significant difference in iron concentration between white maize and PVA-biofortified maize. Furthermore, the results of the current study indicate that, regarding iron concentration in the composite dishes, there would be no benefit in replacing white phutu
with PVA-biofortified phutu
in the composite dishes, with respect to the iron and zinc concentration (Table 7
). However, curried chicken contains a higher iron content, thus implying that if it were consumed together with PVA-biofortified phutu
this could improve the iron intake of vulnerable populations. However, as mentioned earlier, chicken is unaffordable to many. Therefore, the more affordable combination, phutu
and bambara groundnut curry, could be an alternative to improve the protein and micronutrient content of human diets. However, it needs to be emphasised that there is an urgent need to test consumer acceptability of this composite dish as it is not commonly consumed, especially in South Africa. Further studies could also investigate the effect of combining iron biofortified beans with PVA biofortified phutu
, on the iron concentration.
Although fibre and total mineral concentrations were higher in OFSP than CFSP, the protein content of the OFSP was lower (Table 2
). The OFSP of this study was high in iron concentration but low in zinc concentration, compared to the CFSP (Table 8
). The results suggest that the OFSP could be used to improve the iron content of dishes in which sweet potato is a major ingredient, and, thereby, contribute to alleviation of iron deficiency among target communities. The OFSP could be composited with locally available, affordable food item/s rich in zinc, to simultaneously address zinc deficiency.
Although, the protein content of the OFSP of this study was lower than that of the CFSP, it was higher than the values reported by Sanoussi et al., who found that the protein content ranged from 2.03-4.19 g/100 g, DW in pale-dark orange sweet potato [61
]. The results of the current study and previous studies indicate that OFSP generally has a low protein content, and there is a need to develop the OFSP further to increase its protein content. Despite its low overall protein content, the concentration of the essential amino acid lysine was higher in OFSP than in the CFSP (Table 5
). The consumption of OFSP could contribute to improving the fibre and iron content in the diets of vulnerable individuals. It is noteworthy that the current study did not investigate the nutritional composition of composite dishes comprised of OFSP and other locally available, affordable other food item. Furthermore, consumer acceptability of OFSP should be investigated and, if necessary, improved to ensure that OFSP would be consumed by the target population groups.
This study investigated the effect of replacing white maize and CFSP with PVA-biofortified maize and OFSP on the nutritional composition of traditional dishes. With respect to the protein and lysine concentration, the results of the current study indicate that there would not be an advantage in replacing white maize with PVA-biofortified maize (Table 1
). This result is obviously because the protein content in white maize was not significantly different from PVA-biofortified maize. In contrast, Pillay et al. found that PVA-biofortified maize had a higher protein concentration than white maize [60
], whereas Oluba and Oredokun-Lache found that white maize had a significantly higher value than PVA-biofortified maize [62
]. The reason for the differences seen in protein concentration could be attributed to genetic and/or environmental factors. However, this study did not develop PVA-biofortified maize to improve the protein content, but focused on whether the PVA carotenoid and micronutrient content was increased. This was the reason why our results also indicated that PVA-biofortified maize had a similar lysine concentration to white maize (Table 3
The protein content of dishes containing PVA-biofortified maize could be increased by combining the biofortified maize with protein-rich food items. For example, in the current study, when PVA-maize was combined with chicken curry, the composite dish had a higher protein content compared to PVA-biofortified phutu
alone. This was expected, because, generally an animal food product such as chicken contains a higher protein content and quality than plant products; this is confirmed by the results of the current study where the curried chicken had a higher lysine content than all three plants products, PVA-biofortified phutu,
curried cabbage, and curried bambara groundnut. Thus, combining PVA phutu
with chicken curry would result in an improved protein content of the composite dish. However, the challenge is that chicken is not affordable to a large proportion of population groups in South Africa, especially those living in rural areas of KZN, where poverty and food insecurity are prevalent [43
]. Although the protein concentration of the two composite dishes PVA phutu
and cabbage curry, and PVA phutu
and bambara groundnut curry were not significantly different (Table 1
), the protein concentration of the composite dish containing bambara groundnut curry was higher numerically. It is well known that legume grains generally contain higher concentrations of protein than leafy vegetables. Furthermore, legumes contain adequate concentrations of lysine and tryptophan, whereas cereal grains contain an adequate concentration of methionine, but lysine and tryptophan are limiting [63
]. Combining maize with a food item that is higher in lysine and tryptophan would improve the protein quality of the diet [64
]. The deviation from this norm observed in this study could be attributed to the statistically small sample size. Therefore, it is still recommended that PVA phutu
is combined with bambara groundnut curry rather than cabbage curry to improve the lysine concentration, thus improving the overall protein quality of the composite dish. Composite dishes with an improved protein content would be highly beneficial, especially to individuals that suffer from protein-energy malnutrition. This condition is caused predominately by a deficiency in protein and energy and leads to several serious health conditions [64
]. Providing an affordable composite dish that combines PVA-biofortified phutu
and bambara groundnut would not only contribute to reducing VAD, but also malnutrition. The main challenge with incorporating bambara groundnut into the diet of vulnerable groups is that this legume is not a common food source in South African [53
]. It seems there are no published studies on consumer acceptability of composite dishes in which PVA phutu
is combined with other food items such as cabbage and bambara groundnut. Thus, further investigation of consumer acceptability of these composite dishes would be required.
The introduction of biofortified crops could provide nutritious, affordable food sources whose consumption would contribute significantly to improving the vitamin A status of the vulnerable population groups. The biofortified crops could be composited with underutilised nutrient-dense indigenous crops, such as bambara groundnut, to further fortify the dishes with essential nutrients and protein.
The present study indicates that replacing white maize with PVA-biofortified maize in all the three composite dishes studied resulted in an improved PVA carotenoid content. Although the PVA phutu and chicken curry is the ideal composite dish for improving the PVA carotenoid content and protein quality, the composite dish containing PVA phutu and bambara groundnut curry would be a more affordable alternative, as it also has a high PVA carotenoid content and would likely have both high protein quality and content, due to the complementary protein phenomenon. There was no significant difference in the iron and zinc concentration of all the three composite dishes containing PVA phutu. The results further indicate that bambara groundnut would be a suitable alternative food source for compositing with provitamin A (PVA)-biofortified maize to improve the nutritional value of the traditional dishes that normally contain white maize as the main ingredient. However, consumer acceptability of the composite dishes containing bambara groundnut should be investigated further as the legume is not familiar to most South Africans.
The orange-fleshed sweet potato (OFSP) had high PVA carotenoid, fibre and iron concentration and a lower protein concentration compared to the cream-fleshed sweet potato (CFSP). The OFSP has the potential for improving the vitamin A status of VAD-vulnerable population groups in South Africa, if consumed with another food item, especially a protein-rich food, such a composite dish, would contribute to combating both VAD and malnutrition.
Overall, the findings of the current study indicate that Provitamin A-biofortified phutu when combined with other foods, such as curried cabbage, chicken or bambara groundnut and OFSP have the potential to improve nutrient intake and dietary diversity of the rural population groups in KZN and other rural areas of South Africa. The proposed composite foods would be new to the target population groups, as such it is not known whether they would be acceptable to the consumers. Therefore, future studies should investigate the sensory acceptability and consumer perceptions of combining PVA-biofortified phutu with either cabbage, chicken and bambara groundnut and OFSP.