Density and viscosity of cold flour pastes of cassava ( Manihot esculenta Grantz), sweet potato ( Ipomoea batatas L. Lam) and white yam ( Dioscorea rotundata Poir) tubers as affected by concentration and particle size

Abstract

The effect of tuber type, paste concentration and flour particle size on the density and viscosity of cold pastes were investigated. The first set of samples were pastes of 5%–50% (w/w, db) of 180 μm flour particles. The second were 10% (w/w, db) pastes of varying size (75–500 μm) of flour particles. Results showed that both the density and viscosity of sweet potato (SP) were highest and significantly different ( P<0.05) from those of cassava (CS) and white yam (WY). The density and viscosity correlated directly ( r>0.95) and significantly ( P r <0.005) with concentration and inversely ( r<−0.75) and significantly ( P r ≥0.005) with particle size. Analysis of variance (ANOVA) indicated that the influence of tuber type was significant ( P<0.01). The density and viscosity for the 40% paste were not significantly different from those of 35% and 45% pastes ( P<0.05). The viscosity and density of the 75 μm sample were significantly higher than those of any sample with larger particle size. These observations showed that tuber type, concentration and particle size are all crucial factors determining the density and viscosity of tuber flour pastes. The experiment has shown that when high concentrations of SP flour with ≤180 μm particle size are incorporated in foods, large changes in viscosity and density would be obtained.