Acceptability of Vegetable Fortified Ugali in Sub-Saharan Africa

Abstract

Corn flour-based porridge like dough, ugali, is the staple food of low-income population in sub-Saharan Africa. Lack of vitamin A, carotenoids, and dietary fibers brings about serious health issues to this population. In this study, vegetables including bok choy, broccoli, cabbage, carrot, Chinese onion stalk (C_onion), mushroom, are added during the cooking of ugali, as nutritional supplements. The freeze-dried powder of each vegetable was used for its long storage, stable nutrients, and similar particle size. Sub-Saharan African assessors were trained and sensory evaluated the six different vegetable fortified ugali with the plain, unfortified as the control on five attributes. The plain ugali was indistinguishable with the C_onion stalk fortified in color, with the carrot and C_onion stalk fortified in odor, with all vegetables (except broccoli and mushroom) fortified ugali in taste, with carrot and C_onion stalk fortified in granularity, and with cabbage, carrot, C_onion stalk fortified in viscosity. Preference ranking analysis showed that the C_onion stalk fortified ugali is even more favorably preferred than the plain, unfortified ugali, probably due to the umami components in C_onion that serve as the taste enhancer. This study indicates that Chinese onion stalk is a potential vegetable supplement to population in the sub-Saharan Africa.

1. Introduction

In several sub-Saharan African countries, corn, cassava and sorghum are common crops whose yields merely satisfy local demands [1]. These crops are often ground into powder, mixed with water, boiled to cooked, and served as the staple food in a number of sub-Saharan African countries (Figure 1). Ugali is a stiff, starchy porridge made from flour of various crops which is prepared by gradual mixing of the flour with boiling water. When the flour-boiling water mixture is allowed to simmer further, the starch-rich slurry transforms into a viscous porridge as a result of gelatinization of the starch [2]. Depending on the country, ugali is usually served with side dishes of stews containing various relish like fish, legume, cooked green leafy vegetables, beef, sour milk or other sources of protein [3,4]. Although the ugali itself is known to be extremely low in terms of nutrition content, it is the quality and quantity of these side dishes that can potentially improve their nutrition value [4]. However when ugali is served with relish which is also low in nutrition value as is the case in most rural areas in sub-Saharan African countries, then the combined meal still remains of low caloric and nutritional value [4].

There are many names of this food according to the countries, regions, even tribes. It is most widely called ugali, which is also named as bugali, gari, nshima, pap, etc. in different countries (

Table 1. Appellations of the same staple food in different African countries.

Appellation	Country
Bugali	Burundi, DR Congo, Rwanda
Chima	Mozambique
Isitshwala	Botswana
Gari	Gabon
Kaunga	Uganda
Mealie pap	Lesotho, South Africa
Mutuku	South Africa
Ngima	Kenya
Nkima	Kenya
Nshima	Malawi, Zambia
Nsima	Malawi, Zambia
Oshifima	Namibia
Pap	Namibia, South Africa
Papa	Lesotho, South Africa
Shima	Malawi
Ubugali	Rwanda
Ugali	Kenya, Malawi, Mozambique, Tanzania, Uganda
Upswa	Mozambique
Vhuswa	Venda
Xima	Mozambique

). Here we refer it to ugali as it is the name by which it first appeared in a nutritional study 33 years ago [5]. Normally, ugali is made with only white corn flour, but when the corn has a bad harvest, sorghum or cassava powder would be used instead to make ugali. Acting as the staple food for 250 million African people, if cassava is used in making ugali instead of corn, it seriously lacks zinc, iron, vitamin A and proteins [6,7], and contains cyanides that would cause nervous system damage to 5% African children after long term ingestion [8]. The low content of tryptophan and lysine in corn also renders insufficient protein in terms of nutrition need. Previous study revealed that after long-term ingestion of ugali as the only food, all the experimental rats displayed liver diseases to varying degrees [9]. These were mostly diffuse hepatic enlargement and extensive nodular cirrhosis caused by fat changes. In all, long term and sole intake of only ugali as the staple food introduces nutritional deficiency related health issues. One way to solve the undernutrition caused by intake of ugali as the sole staple food may commence with corn cultivation that trying to improve its nutrition content. Previous study shows that for the crops (mainly beans, rice, millet, cassava and corn) cultivated in South Asia, sub-Saharan Africa and Latin America, nutrition enhancement in minerals and carotene could apparently help suppress the symptom of iron and vitamin A deficiency for local people. Meanwhile, their physical, mental and cognitive abilities were significantly improved [10]. Promotion of vitamin A fortified sweet potato in Uganda and Mozambique showed that children and women in Uganda who consumed fortified sweet potato had a significant increase in vitamin A intake, while the Mozambican children also had a significant increase not only in vitamin A but also other vitamins [11,12]. However, it has proven to be a challenge to persuade the local people in some countries, especially the elderly to adopt these nutrition-enhanced crops when they are so used to either cultivating and/or consuming the old varieties that they are familiar with while they are unsure of the crop yield of the nutrition enhanced-varieties [13,14]. However, a recent study has reported much improved acceptability of these fortified varieties in a number of African countries [15].

Another way to solve the nutrients deficiency in the staple food ugali is to add vegetables or fruits in ugali. Forsido et al. had tried adding Ethiopia banana to this Africa staple food, finding that the content of calcium and dietary fiber increased, so it was considered to have the potential to be applied in preparing this staple food [16]. When one considers adding fruits and vegetables to ugali for nutritional value increasing purposes, vitamin A or pro-vitamin A (β-carotene and carotenoids) should be considered with high priority as aforementioned. Bok choy, carrots, and cabbage have been supplied in meals to improve the total-body vitamin A pool size [17]. Broccoli, the Chinese onion (C_onion, Allium schoenoprasum), and mushroom (Lentinus edodes) are not only rich in vitamin A or carotenoids but also may add favorable flavors to ugali [18,19,20]. Dietary fiber has been proven beneficial through nourishing the gut microbiota [21,22]. Three types of flour paste from white corn (maize) can be used for making ugali depending on the how the white corn is processed [23]. Whole maize flour is produced from milling the dry maize without removing bran and is hence rich in fiber. Dehulled flour involved dehulling and winnowing to remove the bran and then milling the rest to produce the flour. Fermented flour, which is the most common, involved soaking (partially fermenting the maize grits for a day or two), washing and sun drying the maize grits before milling. Potentially, nutrients of dietary fiber are lost during the dehulling and winnowing stage when bran is removed [24] Fortification of watermelon pulp to another maze based food Mageu was tried, however, fruit fortification does not supply dietary fiber as vegetables do [25]. Thus, addition of dietary fiber through vegetable fortification, such as the Chinese onion stalk, is beneficial for the sub-Saharan population [26]. In this study, we chose bok choy, broccoli, cabbage carrot, Chinse onion (the stalk, C_onion), mushroom as the supplementary vegetables, for their rich content in either vitamin A, carotenoids, dietary fiber or both (Figure 2).

Freeze drying of vegetables not only enhances storage stability, reduces transportation weight, maximally maintains micro-nutrients, but also enables grinding of vegetables to powders that allows fortification into ugali [27,28]. The present study mainly focused on the sensory acceptability of freeze-dried vegetable powder fortified ugali to population with ugali as the staple food, as an evaluation of the feasibility of promoting vegetable fortified ugali in sub-Saharan Africa.

2. Materials and Methods

2.1. Materials

White corn flour was purchased from the supermarket for international students at the west campus of China Agricultural University. The freeze-dried vegetable of bok choy (Brassica rapa subsp. chinensis), broccoli, cabbage, carrot, C_Onion, mushroom (Xianggu, Lentinus edodes) were purchased from Jiangsu QingGu Foods Co., Ltd. (Xinghua, Jiangsu Province, China).

2.2. Preparation of Vegetables Foritfied Ugali

The freeze-dried vegetable was ground to the same particle (100 mesh) size before use. The white corn flour of 100 g was added gradually to 200 mL of boiling water and kept stirring all the time. Based on the nutritional value of each vegetable, 20 g could meet the daily requirement of nutritional intake of vitamin A, carotenoids, and dietary fiber. For vegetable fortified ugali, 20 g of each vegetable power was added during the stirring of ugali cooking, respectively. Heating and stirring was stopped until the corn flour was thoroughly cooked, and each cooked ugali was chilled before applied to sensory evaluation.

2.3. Sensory Evaluation

Sensory analysis of ugali was principally the same as previously performed on soymilk and chickpea [29,30,31]. The evaluation was conducted under white light and standardized conditions at the China Agricultural University, and each assessor was assigned a consent form prior to taking part in the study. After reading the consent form, assessors were asked if they understood the purpose and objectives of this study, procedures for assessing the cooked ugali, confidentiality of respondents and data, and the right to withdraw. Signed consent forms were collected from the assessors for record keeping purposes. After exclusion of assessors who were allergic to the abovementioned vegetables, a total of 24 assessors (international students in China Agricultural University from sub-Saharan African countries, 16 males and 8 females, aged 24–42 years old) were selected. The culinary traditions for ugali consumption in these countries are similar.

A “questionnaire” was provided to each assessor and they were requested to fill their gender, age and nationality (optional). Assessors were allowed to test 8 ugali samples in two sessions, 4 samples in each session and there was a 10 min break between sessions. In one session, assessors were required to clean their mouth with drinking water before and after assessing each sample, and take a break for 10 s between two samples. In each session, one plain ugali sample (with no vegetable addition) and three other vegetable fortified samples were offered with random sample codes (271, 472, 374, and 881 for the first session, 574, 331, 798, and 358 for the second session) and the content of the sample information was kept unknown to assessors. The samples were presented in small, transparent plastic containers, marked with the corresponding code, served with a spoon and a cup of drinking water. For one ugali sample, assessors evaluated five attributes including: color, odor, taste, granularity and viscosity. Assessors used a nine-point hedonic scale (from −4 = disgusting, 0 = neutral, to 4 = yummy). Finally, assessors were asked to rank the samples in order of preference (1 = least preferred, 8 = most preferred). The questionnaire was collected and data was processed.

2.4. Data Analysis

Sensory evaluation data of five attributes for two repeats of plain ugali were combined, and sample differences on each attribute were analyzed with least significant difference (LSD) test at a significance level of α = 0.05 with SPSS Statistic 26.0 (IBM Corp., Armonk, NY, USA). The violin plots were plotted with the GraphPad Prism (version 8.0, GraphPad Software Inc, La Jolla, CA, USA).

For median caregiver sensory rating, data of five attributes were compared by non-parametric Friedman’s two-way analysis of variance by ranks (p < 0.05) [29].

For preference ranking analysis, the sum of the rank for each sample was calculated, and that of the two blank groups was averaged. The ranking data was analyzed by Friedman test at a significance level of α = 0.01 to evaluate significant differences among all samples [32]. The test statistic F is calculated in Equation (1) where R_i is the sum of ranks for sample i; n and K are the number of valid assessors and samples, respectively.

$$F = \frac{12}{nK\left(K+1\right)}·(R_1^2+R_2^2+\cdots +R_K^2)-3n\left(K+1\right)$$

(1)

The test statistic F exhibits an asymptotic Chi-square distribution with K−1 degrees of freedom. At the α significance level, there are significant differences among all samples if F ≥ ${\chi }_{K-1;\alpha }^2$, where ${\chi }_{K-1;\alpha }^2$ is the α quantile of the Chi-square distribution with K−1 degrees of freedom. The significant differences between ranking data of two samples were analyzed with LSD test with SPSS Statistic 26.0 at a significance level of α = 0.05.

3. Results

Generally, the sensory evaluation process can be divided into two steps. The assessors were allowed to observe and smell the ugali samples before they try to taste them. And the initial observation and smelling of the sample profoundly impact personal willingness to taste. Thus, sensory evaluation data are divided into pre-tasting and tasting part for discussion.

3.1. Pre-Tasting Senseory Evaluaiton of Differently Fortified Ugali

The plain, corn flour-based ugali exhibited a white color with tint yellow (Figure 3A, B). Addition of different freeze-dried vegetable powder apparently altered the color of ugali. Specifically, addition of bok choy, broccoli, and cabbage endowed ugali a green color, with decreasing extent. That is, bok choy endowed ugali a dark green color (Figure 3C), broccoli endowed ugali a green color (Figure 3D), and cabbage endowed ugali a light green color (Figure 3E). On the other hand, addition of carrot endowed ugali a pink color (Figure 3F), addition of Chinese onion stalk endowed ugali a tint yellow color (Figure 3G), while addition of mushroom endowed ugali a brown color (Figure 3H).

Sensory evaluation of the color by assessors discriminated the color of plain ugali with these fortified with bok choy, broccoli, cabbage, carrot, and mushroom (Figure 4A, p < 0.05), but not with ugali fortified with Chinese onion stalk. For ugali added with bok choy, broccoli and cabbage, there is no significant difference among them in presenting the green color. Interestingly, there is also no significant difference between ugali fortified with cabbage, carrot, and Chinese onion stalk. What’s more, ugali fortified with mushroom looks apparently less preferable by color from these fortified with cabbage, carrot, Chinese onion stalk, and the plain ugali (p < 0.05), but not with ugali fortified with bok choy or broccoli.

Sensory evaluation of the odor by the assessors discriminated the odor of plain ugali with these fortified with bok choy, broccoli, cabbage, and mushroom that showing less preferable hedonic scale (Figure 4B, p < 0.05), but not these fortified with carrot and Chinese onion stalk. Meanwhile, there is no significant difference between carrot fortified ugali and these fortified with bok choy, broccoli, cabbage, Chinese onion stalk and mushroom. On the other hand, Chinese onion stalk fortified ugali distinguished itself from every other sample (p < 0.05) except carrot fortified- and the plain ugali.

3.2. Tasting Sensory Evaluation of Differently Fortified Ugali

While the plain, corn flour based ugali has no special flavor, different vegetables addition gives different flavor to ugali that may or may not satisfy its consumers. The taste was sensory evaluated to examine the catering to the potential consumers of each vegetable fortified ugali. Among all the vegetable added ugali, only the broccoli and mushroom added ugali exhibited significant less favorable responses in taste than the plain ugali (Figure 5A, p < 0.05). Meanwhile, the taste is indistinguishable from broccoli added ugali and bok choy, cabbage, carrot, mushroom fortified ugali. And the taste of mushroom added ugali is indistinguishable from bok choy, broccoli, and cabbage added ugali.

Although all vegetable powders were ground to the same size, they were all larger than the fine corn flour particles used in this study. The differences in the vegetable textures may introduce a variable in the mouth feeling that influences consumer experience. The granularity was sensory evaluated to exam the acceptance to the potential consumers of each vegetable fortified ugali. Among them, bok choy, broccoli, cabbage, and mushroom added ugali is significantly less preferred from the plain ugali as assessors evaluated (Figure 5B, p < 0.05). And there is no distinguishable granularity difference between the plain, carrot and Chinese onion stalk added ugali.

Ugali itself is a half-solid, half-liquid, viscous, porridge like food. Fortification with different vegetables may impact its viscosity that influences consumer mouth feeling. The viscosity was sensory evaluated to exam the acceptance to potential consumers of each vegetable added ugali. The cabbage, carrot, and Chinese onion stalk fortified ugali exhibited no differences in the mouth viscosity compared with the plain ugali. While there is a significant sensible viscosity difference between the plain ugali and the bok choy, broccoli, and mushroom added ugali (Figure 5C, p < 0.05).

3.3. Caregive Acceptability and Preference Ranking of Differently Fortified Ugali

Caregiver evaluation of the five attributes of differently fortified ugali showed that all the sensory attributes, that may affect the acceptability of ugali, changed significantly with the addition of vegetables (Figure 6A). Using the plain ugali (blank) as a food vehicle, caregivers were able to detect differences between fortified ugali for color, odor, taste, granularity, and viscosity (p < 0.05). For all the attributes, ratings were undesirable for every fortified ugali, except Chinese anion stalk that is almost as identically desirable as the plain, unfortified ugali.

The preference ranking sequence of the seven flavors of ugali was: Chinese onion stalk-fortified, carrot fortified, cabbage fortified, blank (unfortified), broccoli fortified, bok choy fortified, and mushroom fortified (Figure 6A). However, except that the Chinese onion stalk-fortified ugali was significantly ranked higher than others (p < 0.05), ranking among other fortified ugali was not significant. Similar survey with a much larger population might resolve the differences between the preferences of different fortified ugali in the future.

4. Discussion

Five attributes of the plain and vegetable fortified ugali, color, odor, taste, granularity, and viscosity, were evaluated by assessors. Since people usually sensed color and odor before they further taste it, which includes taste, granularity and viscosity, we decided to discuss color and odor before taste, granularity and viscosity. Plain ugali exhibited a white, yet tint yellow color that easily distinguish it from any fortifications except Chinese onion stalk due to the light and similar color of the later. Bok choy, broccoli and cabbage all endowed ugali green color due to the chlorophyll in them with non-distinguishable extent to consumers. It seems that color alteration with tint colors does not distinguish themselves, as evidenced by the indistinguishable hedonic scale of ugali fortified with cabbage, carrot and Chinese onion stalk. Deep brown color, endowed by addition of bok choy, broccoli, and mushroom does not differentiate each other for consumers. Although the odor of carrot (endowed by the presence of linden ether) added ugali is the same to consumers as the plain ugali, the color between them tells the difference [33]. The odor of Chinese onion stalk (probably dipropyl disulfide and methyl propenyl disulfide) fortified ugali was statistically unidentifiable from that of plain ugali [34].

From the taste perspective, plain ugali and the Chinese onion stalk fortified one were unidentifiable from bok choy, cabbage, and carrot added ones. This is probably due to the rich flavor content in broccoli and mushroom that distinguished themselves [35,36]. Oral texture properties of ugali often limits the nutrition intake, especially in children, leading to protein-energy malnutrition [37]. The oral cavity sensation of granularity between the plain, carrot and Chinese onion stalk added ugali is the same to the potential consumers. This is probably due to the reason the highly rehydration process of freeze-dried carrot and onion stalk during ugali cooking that their texture differences between the plain ugali were eliminated [38]. The viscosity of plain ugali is indistinguishable from that of cabbage, carrot, and Chinese onion stalk fortified ugali. This is probably due to the absence of starch or second thickener in the fortified ugali system [39].

In summary, the Chinese onion stalk fortified ugali exhibited no significant sensory differences in color, odor, taste, granularity and viscosity compared with the plain, unfortified ugali for assessors. Both the caregiver evaluation and preferencing ranking indicates that assessors even preferred the Chinese onion stalk fortified ugali over the plain one. Another Allium vegetable, Allium hookeri, significantly increased its sourness, sweetness and umami taste after hot air-dry [40]. The overall preference of the freeze-dried Chinese onion stalk fortified ugali is thus highly likely due to the presence of sweetness and umami components in this vegetable, not serving to change the taste, but as a taste/flavor enhancer for the plain ugali [41,42,43].

This study is one of its kind in this area and will hopefully result in more studies with larger sample sizes investigating the possibility of improving the nutritional value of ugali through the use of vegetable pastes proposed in this study and more. However, although these vegetable pastes have been found to be a potential source of nutrition when added to ugali, one anticipated limitation to their use would be their availability in the different African countries where ugali is the staple meal. If already readily available in most if not all of these countries, then follow up in-country studies should be conducted to determine the acceptability of such mixtures by the actual local people. Although the side dishes commonly served with ugali in various countries might have some nutritional value, the results of this study show some promising results that in the areas where such high-nutritional value side dishes are not guaranteed, consumption of ugali fortified with the vegetable pastes reported in this paper could be an ideal option.

5. Conclusions

To increase the nutritional value of corn flour based ugali, specifically in vitamin A, carotenoids, and dietary fiber, freeze-dried powder of bok choy, broccoli, cabbage, carrot, Chinese onion stalk, and mushroom were added during ugali cooking. Fortification with these vegetables either changed the color, odor, or the taste, granularity, and viscosity that eventually lead to unfavorable assessor preferences. Except that the Chinese onion stalk fortified ugali cannot be distinguished from the plain, unfortified ugali while gained more favorable assessor preferences. This is probably due to the presence of umami components in the Chinese onion that serve as taste enhancer, thus renders this vegetable a promising candidate as vegetable supplement for the sub-Saharan Africa staple food. Meanwhile, on the basis of acceptance, bok choy, broccoli, cabbage and carrot variants had a comparable rating to that of plain ugali. Secondly, when the nutritional value was used as the basis, carrot, bok choy and onion stalk was found to considerably improve the micronutrient composition of ugali. Based on these findings, in addition to the Chinese onion stalk, bok choy and carrot options seem to be acceptable candidates for fortification which could be tested further in a follow up study involving a larger sample size.