Physicochemical and Pasting Characteristics of Water Yam (D. alata) in Comparison with Pona (D. rotundata) from Ghana

The physicochemical and pasting characteristics of 18 varieties of Dioscorea alata (an underutilized yam species) were determined in comparison to pona, (a local and most preferred Dioscorea rontundata variety in Ghana) to contribute to knowledge base of D. alata for product diversification and further improvement. Tubers were randomly selected and moisture content determined before processing the remaining to flour for physicochemical and pasting characteristics. The results showed that test varieties had significantly (p<0.05) higher moisture and protein contents, higher peak time and pasting temperature but lower dry matter and starch content, lower swelling power and pasting viscosities in comparison with pona. Peak viscosity ranged from 74.80 to 284.60 RVU, trough (66.85 to 258.65 RVU), and breakdown (19.50 to 311.50 RVU). Peak time and pasting temperatures were 5.15 - 7.00 min and 83.60-90.10oC respectively. Pona had 291.17 RVU as peak viscosity, 186.17 RVU troughs, 105.00 RVU breakdown and 422.75 RVU final viscosity. Others were: setback (236.58 RVU), peak time (4.73 min) and pasting temperatures (79.88oC). The physicochemical properties in conjunction with the pasting properties of the test varieties suggest the presence of strong bonding forces within their starch granules. Pastes from test varieties were relatively more stable when cooked hence will have a lower tendency to undergo retrogradation during freeze/thaw cycles than the reference variety. The study has shown significant variations among D. alata varieties and between the D. alata and pona. This could lead to selection and improvement of D. alata varieties for specific food applications to stimulate their production and utilization.