Investigation of Nutrient and Anti-nutrient Composition of Dioscorea cayenensis-D.rotundata complex
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Date
2011-03
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Addis Abeba University
Abstract
Dioscorea species (Yams) rank as the world’s fourth most important tuber crop in economic
terms and make a significant contribution to diets in some rural areas of Ethiopia where Ethiopia
is one of the major producers in East Africa. However, there is insufficient study on their
nutritional value and anti-nutritional composition. This study was designed to evaluate the
proximate, mineral and anti nutritional composition of yam tubers (Dioscorea cayenensis-
rotundata complex) collected from Sheko wereda, Bench Maji zone, South Nations, Nationalities
and people’s Regional state. Effect of household processing methods namely boiling and frying
on composition of Dioscorea was also investigated. To determine the proximate, mineral and anti
nutritional composition chemical analysis were conducted using standard procedures. Data were
analyzed using SPSS (SPSS Software for windows release 16.0; SPSS Inc., Chicago, IL, USA).
In raw yam tubers, moisture was high 69.56 ± 0.2% for the yellow and 73.44±0.5% for the white
tubers. Crude protein content was 1.85±0.04% for the yellow and 2.03±0.03% for the white
tuber while ash was highest (4.10±0.01%) in the yellow 4.62±0.01% in the white tuber. Crude
fat was low in both tubers 0.35±0.01% for the yellow and 0.18±0.01% for the white tuber while
total carbohydrate was high in both tubers 20.95±0.1% and 19±0.06% for the yellow and white
tubers respectively. The fiber contents were 3.19+
0.05% for the yellow and 2.68+0.03% for the white tubers. Calcium and potassium were the major minerals found in both tubers. calcium
contents of 52.55+
0.01 and 60.52 +0.01 and potassium contents of 53.33+0.33 and 45.73+0.01
were found for the yellow and white tubers respectively. Phytate, tannin and oxalate contents
were 38.2+0.002, 22.2+
0.001 and 0.006+0.001 for the yellow tuber and 34.8+0.002, 28.8+0.001
and 0.006+
0.001 for the yellow tuber. There were no significant difference (p>0.05) in the
proximate, mimeral, phytate, tannin and oxalate contents of the raw tubers of the yellow and
white varities. Boiling and frying significantly reduced (P<0.05) the level of phytate, tannins and
oxalate in both tubers.
Both tubers are found to be a good source of crude fiber, carbohydrate and minerals. The anti
nutritional factors (phytate and oxalate) found in both the investigated tubers were lower than
previous reports. Both boiling and frying seem to be best for the removal / inactivation of anti-
nutritional factors. In terms of energy, if consumed at 350g per day, none would meet the FAO
recommended values. The investigated samples can not be consumed as the sole source of
energy to humans. In order to derive full nutritional potential from the yellow and white yam,
they should be consumed together with protein-and fat-giving foods.
Description
Keywords
D.cayenensis-D.rotundata complex, proximate composition, anti-nutritional factors