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Effect of full-fat soya bean flour on the quality and acceptabiIity of fermented cassava flour

Festus A. Numfor and L. Noubi


In an attempt to improve the nutritional value of fermented cassava flour, studies were carried out to determine the effect of the addition of full-fat soya bean flour on its quality and acceptability. The results showed that protein, total lipids, phosphorus, iron, ash content, and gross energy increased with increased proportion of soya bean flour. The viscosity of gels of the composite flour decreased with decreased proportion of cassava flour. At a 10% level of substitution of cassava with full-fat soya bean flour, there was no noticeable difference in the organoleptic qualities of the composite product and that obtained from pure cassava flour alone. At this level, the protein content was about 7%. Eighty-four percent of participants rated the product good to excellent in an acceptability test of fufu (a dough made from cassava flour) made from 10% soyasubstituted flour in west and east provinces of Cameroon.


Protein malnutrition is a major public health problem in some parts of Cameroon [1]. Diets in these parts are predominantly starchy, the major food crops being roots and tubers [2]. From 24% to 88% of the daily calories of populations in these regions are said to be derived from cassava alone.

In Cameroon cassava is traditionally processed into a wide range of products, one of the most important of which is a fermented flour called couscous or kumkum. The flour is usually made into a hot water dough ( (fufu) and eaten with soup, which, depending on the family income, may or may not supplement the low protein content of fufu. Unfortunately, the majority of people in these zones cannot afford this supplementation, which in most cases is in the form of expensive animal proteins.

Cultivation of the soya bean (Glycine max) is gaining ground in Cameroon. Soya bean has a high protein content and is not very expensive. Therefore it has been proposed as an ideal source for protein supplementation of starchy foods [3]. Extensive cultivation and use of this crop are being promoted by Projet Soja, a rural development organization.

Two principal methods are available for increasing the protein content of fermented cassava products. First, through controlled fermentation, microflora could be made to grow in large numbers in the mash [4-6]. The method. however, involves advanced techniques that cannot be performed easily by the people in the target areas. Furthermore, cassava products enriched by this method have thus far been destined only for animal feed, due to the high risks involved in microbial manipulations.

The second method involves adding protein to the deficient food from external sources in such a way as not to alter significantly the organoleptic qualities of the original food [3, 7]. This method has an advantage over the first because of the open choice of protein sources, its simplicity for use by groups with low technological capabilities, and its relative cheapness. In our case, soya beans were chosen because other plant protein sources are traditional in the diets of the people. Also, they were chosen to fulfill one of the national objectives of integrating the use of this new and important crop into the diets of the people of Cameroon.

FIG. 1. Flow diagram for preparing cassava-soya bean come posite flour

Materials and methods

Soya bean (variety SJ 299) supplied by Projet Soja, UCCAO, Bafoussam, and local njombe cassava were used. Full-fat soya bean flour, fermented case save flour, and their composites were prepared as shown in figure 1 [8].

Cassava flour was substituted with the full-fat soya bean flour at 0%, 5%, 10%, 15%, and 20% levels. After thorough mixing, samples were withdrawn for chemical, rheological, and acceptability tests. Proximate analyses using standard laboratory methods were carried out at the Nutrition Centre, Yaounde. Crude protein (N x 6.25) was determined by the micro-Kjeldahl method [9]. and total ash was determined by ashing for 12 hours at 550°C. Total lipids were estimated by petroleum ether extraction. The Gallenkamp bomb calorimeter was used to determine gross energy. Phosphorus and iron contents were determined by atomic absorption spectrophotometry [9]. Starch content was estimated as the difference on a dry weight basis.

Viscosity studies using a Brabender amylograph (C.W. Brabender Instruments Inc., South Hackensack, NJ, USA) were performed at the International Institute of Tropical Agriculture, Ibadan, Nigeria. Fifty grams of the flour or its composite was placed in the bowl of the instrument, 450 ml of water at room temperature was added, and the apparatus was switched on. The, pasting performance of the flour was automatically recorded on the graduated sheet of the amylogram.

Doughs (fufu) were prepared using each of the five composite flours and rated on a 10-point hedonic scale by a trained laboratory panel for texture, colour, taste, and overall acceptability (data not included). The 90% cassava-10% soya bean dough scored highest, and hence its flour was selected for subsequent consumer acceptability test. The product was packed in 1-kg lots in translucent composite polythene bags.

Random samples of 55 and 41 households in the western and eastern provinces of Cameroon, respectively, were used for the acceptability test. Each participant was given a packet of the enriched flour and one of cassava flour alone. A questionnaire accompanied each sample. Instructions were given to the participants to prepare the fufu the usual way, taste it, and then respond to the questionnaire.

Results and discussion

Table 1 shows the results of the proximate analysis of the flours. The protein content of the composite flour increased with increasing proportion of fullfat soya bean flour. At 10% substitution, the level at which the organoleptic qualities of the composite fufu did not differ noticeably from those of the case save flour alone, the protein content was about 7%, compared with about I % for the cassava flour alone. There was also a corresponding increase in most of the other elements with increase in soya bean content. Amylographic studies (table 2) showed that the Brabender viscosity of the composite flour decreased with increase in the proportion of full-fat soya bean flour. However, when 100% soya bean flour was used, only a baseline (18 Brabender units) was obtained in the amylogram, suggesting that the decrease in viscosity of the composite flour was due more to the decrease in the proportion of cassava flour than to the increase in the proportion of soya bean flour. This is explained by the fact that in preparing the full-fat soya bean flour, the available starch is gelatinized by heating. Subsequent heating by the amylograph had very little effect on its swelling capacity. At 10% substitution, there was no noticeable difference between the viscosity at this level and that of 100% cassava flour. Elasticity is a characteristic quality of fufu. The laboratory panel also did not find an appreciable difference between the texture of 10% soy-substituted fufu and that from cassava flour alone. Flour at 10% level of substitution was therefore retained for acceptability tests.

TABLE 1. Composition per 100 g dry weight of cassava-full-fat soya bean flour


Composition of flour (%) Protein(g) Lipids


Starch(g) Ash


Gross energy(mg) Phosphorus




Cassava Soya bean
100 0 1.1 0.2 98 1.1 398 68 6.8
95 5 5.3 2.3 91 1.4 404 103 6.9
90 10 7.5 3.9 86 1.9 408 147 7.8
85 15 10.1 4.4 83 2.4 407 153 9.8
0 100 41.0 23.1 30 5.9 458 516 9.9

TABLE 2. Readings from amylograms showing pasting performance of cassava-soya bean composite flour


Composition of flour(%) Maximum viscosity

(Brabender units)

Pasting temperature(°C)

Cassava Soya bean Initial Maximum
100 0 960 43.5 60 75
95 5 950 42.0 63.0
90 10 870 39.0 63 75
85 15 660 43.5 64.5
80 20 565 42 0 61.5
0 100 18 90 -

TABLE 3. Results of acceptability test of cassava-soya bean composite flour in Western and Eastern provinces of Cameroon

Question Number of responses



West East West East
General appreciation          
very poor 0 0 0 0


poor 3 0 6 0


passable 3 5 6 0


good 14 5 26 12


very good 25 10 46 24


excellent 7 20 13 49


abstention 3 1 6 33 4
easy to prepare 47 33 86 81


difficult to prepare 6 4 11 10


neither easy nor difficult 2 4 4 10


Most appealing factor          
taste 29 19 52 46


flavour 4 3 7 7


colour 3 3 5 7


protein 17 8 30 20


texture 3 8 6 20


Compare with usual fufu          
better taste 22 18 40 44


easier to prepare 17 11 31 27


richer 15 11 27 27


not good at all 1 1 2 2


a. May not add to 100% due to rounding.

The product was rated good to excellent by about 84% of the respondents (table 3). The participants also noted that the composite flour was easier to prepare than cassava flour alone. The decrease in viscosity of the paste was thought to have accounted for this. The participants also commented that fufu prepared from the composite flour was not as white as that from cassava flour alone, probably due to the characteristic yellow pigment in the soya bean flour and browning reactions during processing.


The study showed that adding some full-fat soya bean flour to fermented cassava flour will result in considerable improvement in the flour's protein content and other nutritional elements, such as iron, phosphorus, and gross energy. The adoption and use of this composite flour by populations in which cassava fufu is a staple food will likely contribute to reducing the prevalent protein malnutrition.

Further studies are necessary to determine the full impact of the consumption of such a composite flour on the nutrition status of its consumers, the shelf-life of the product, the economics of large-scale production, and marketing strategies.


Financial support for this study was provided by Projet Soja, UCCAO Bafoussam, Cameroon.


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