Comparative Study on the Properties of Yam (Dioscorea Rotundata) Varieties in Ghana: A Case Study in Asante Mampong

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Four local varieties of Dioscorea rotundata namely Pona, Labreko, Asobayere and Muchumudu were compared by analyzing for their organoleptic, physicochemical and functional properties to ascertain whether these varieties have unique characteristics for particular food products. A survey was initially conducted in Asante Mampong (a yam farming community) and results revealed a high preference for Labreko in terms of eating quality (mealiness, taste and softness). This was confirmed in a sensory analysis test which revealed high scores for mealiness and taste for Labreko; hence Labreko may be promoted for export and local consumption. Significant differences existed in moisture, ash and carbohydrates. Muchumudu had the highest moisture content (74.43%) and may be used for mashed products such as yam pottage. Asobayere had the lowest moisture content (58.91%) and may be exploited for export because of its potential high keeping quality. Carbohydrate contents ranged from 34.24% (Asobayere) to 14.78% (Muchumudu). Mineral analysis showed that Pona was relatively high in iron (4.45 mg/100 g). High calcium (91.60 mg/100 g) and phosphorus (114.50 mg/100 g) contents were recorded in Muchumudu, which is reflective of its high ash content (3.46%). Thus, Muchumudu may be a good source of calcium and phosphorus for growing children. Asobayere had the highest starch yield (20.89%) and may be exploited for starch production. Flours and starches from the yam varieties showed similar trends in amylose contents, swelling power, water binding capacity and some pasting properties. For the starches, amylose content ranged from 27.48 to 31.55%; swelling power ranged from 10.57 to 12.48; solubility index ranged from 8.52 to 9.32% and water binding capacity ranged from 175.25 to 182.69%. There were significant differences (P<0.05) in the pasting properties of the starch samples. The pasting temperature ranged from 75.10 (Asobayere) to 77.30°C (Muchumudu). Labreko and Asobayere may also be used for foods that require shorter processing time such as instant foods because of their low pasting temperatures. The peak viscosity ranged from 614 (Pona) to 726 BU (Asobayere). Asobayere may thus be used for foods that require thick and cohesive paste, gel strength and elasticity. The final viscosity ranged from 385 (Pona) to 817 BU (Muchumudu). The breakdown viscosity ranged from 25 (Muchumudu) to 385 BU (Asobayere). Muchumudu may be used in products that require low viscosity and paste stability at low temperatures. Pasting properties of the flours also followed a similar trend. The results of the study show that Labreko, Asobayere and Muchumudu have unique characteristics which can be used as a basis for their promotion to increase the range of options for consumers on the local and export markets.
A thesis submitted to the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree Master of Science Faculty of Biosciences, College of Science