Date of Award
Master of Science
Food Science and Technology
S.L. Melton, J.R. Mount
This study was conducted to achieve the following objectives: (1) to determine the physical and sensory attributes of the doughs prepared from cassava in which soybean flour was substituted for different amounts of cassava flour; (2) to determine the optimum level of soybean flour that can be substituted for cassava in the doughs; and (3) to evaluate the nutritional value of different mixtures of cassava and soybean flours.
The cassava flour had a protein content of 2.095%, and the commercial defatted soybean flour had a protein content of 53.78% on an air-dried weight basis.
The hydrocyanic acid content of the cassava flour was 5.58 mg of acid/100 g of the flour on the air-dried weight basis. At this level of the acid, a human adult male weighing 50 kg will have to eat about 500 g of the flour mixture to reach the lethal dose of 50-60 mg of hydrocyanic acid. Also, addition of soybean flour to cassava flour has a diluting effect on the acid. Therefore, all mixtures containing soybean flour had less than 5.58 mg of hydrocyanic acid/100 g of flour.
Samples of dough prepared from the different mixtures of cassava and soybean flours were softer than samples prepared from cassava flour alone (control). In order to standardize the consistency of doughs prepared from mixtures of cassava and soybean flours to that of dough prepared as the control, the amount of water added was reduced from that used to prepare a control dough. The following amounts of water were added to 80 g of mixtures containing the different percentages of soybean flour: 250 ml for 0% soybean flour (control); 242.5 ml for 5% soybean flour; 240.5 ml for 10% soybean flour; 233.0 ml for 15%^ soybean flour, and 227.8 ml for 20% soybean flour.
Soybean flour caused cassava dough to darken and become more red and more yellow. At the 20% soybean flour level, the dough was unacceptable to the panel, partly due to yellow color.
A panel of ten students from Tanzania, Kenya, Zambia, Nigeria, and Ghana evaluated the samples of dough for appearance, texture, and eating quality. Considering the three variables tested by the panel, the dough containing 1556 soybean flour was the most acceptable. At his level of soybean flour, the dough was preferred to the control dough. At the 20% level of soybean flour, scores for appearance and eating quality were lower than those of the control dough (see Appendix B). At the 20% level of soybean flour, appearance and taste were unacceptable to the panel, but the texture was acceptable. The dough with 15% soybean flour was scored above 5.0 (like moderately) for appearance, texture, and eating quality. The control sample dough was scored 4.93 for appearance, 2.60 for texture, and 3.63 for eating quality.
Doughs of all the mixtures were deficient in all amino acids but more so for the sulfur-containing amino acids. The dough with 1% soybean flour (most preferred by the panel) provided approximately 30% of the levels of amino acids specified in the FAQ Provisional Pattern.
The protein efficiency ratio (PER) of the cassava-soybean flour mixture (10.56% protein but calculated at 10% protein) was 1.55 with casein serving as the reference t protein (adjusted PER for casein = 2.5). The unadjusted PER value for casein was 2.91.
The rats fed flour mixtures containing 0% and 5% soy bean flour lost weight during the experimental period. During the same period, the mixture containing 10% soybean flour did not cause any weight gain. The 15% and 20% soybean flour mixtures supported weight gain.
This study shows that 15% soybean flour can be added to cassava flour without adversely affecting acceptability of the dough. At this level of soybean flour, the dough was darker, slightly more yellow, and slightly more red than the control dough. Appearance, texture, and eating quality of the dough were acceptable.
The protein content of the cassava flour was increased from 2.09 to 9.95 by adding 15% soybean flour. The amino acid levels of this mixture were below the levels recommended by FAO.
The energy content of the mixture containing 13% soybean flour is sufficient to meet the needs of a "reference" man and a "reference" woman.
Preparing cassava flour for food by sieving, as practiced by East Africans, lowers the protein content of the flour. About 21% of the nitrogen in the cassava meal was non-protein nitrogen.
Temalilwa, Claver R., "Cassava (Manihot esculenta Crantz) flour fortification with soybean flour. " Master's Thesis, University of Tennessee, 1980.