Viscoelastic properties and changes in pasting characteristics of trifoliate yam (Dioscorea dumetorum) starch after harvest

Emmanuel Ohene Afoakwa, University of Strathclyde
Samuel Sefa-Dedeh, University of Ghana

Abstract

Studies were conducted on the viscoelastic properties, as well as the changes in pasting characteristics, of trifoliate yam, Dioscorea dumetorum, starch during post-harvest hardening of the tubers. A 3x4 factorial experiment with blanching treatment time (0, 15 and 30 s) and storage time (0, 12, 24 and 36 h) as the respective variables was performed. The samples were evaluated for pasting temperature, viscosity at 95 _C, viscosity at 95 _C-Hold, viscosity at 50 _C and viscosity at 50 _C-Hold, as well as their changes during storage of the tubers, to determine the starch behaviour of the D. dumetorum tubers during the hardening phenomenon and how blanching affects the process during storage. No significant differences (P40.05) in the viscoelastic properties were observed between the means obtained for pasting temperature, viscosity at 95 _C, viscosity at 95 _C-Hold, viscosity at 50 _C and viscosity at 50 _C-Hold in the white and yellow cultivars studied. Storage caused decreases in all the Brabender Viscoamylograph indices measured. Pasting temperature decreased from 80.4 to 66.6 _C whilst peak viscosity decreased from 30 to 18 BU during the storage period. Viscosities at 95 _C and 95 _C-Hold also declined, respectively, from 30 to 20 BU and 450 to 330 BU within 36 h after harvest. Similarly, viscosities at 50 _C and 50 _C-Hold decreased, respectively, from 450 to 265 BU and 480 to 300 BU during storage of the tubers. Blanching, however, increased the pasting characteristics of the stored tubers. The viscoelastic properties of the two cultivars of D. dumetorum tubers studied were similar. However, the hardening phenomenon causes slight decreases in the pasting characteristics of the tubers after harvest.