On Viscograms and Viscography, With Special Reference to Rice Flour

ABSTRACT Brabender viscograms are usually determined at an arbitrarily fixed starch (or flour) slurry concentration and the resulting peak viscosity (P), breakdown (BD) and setback (SB) values are used as criteria for starch characterization. However, the use of this technique in rice quality research has not been fruitful. A critical review of some of the literature on viscography uncovered a number of fallacies in the above technique. It was revealed that even in a given sample, the magnitude of BD and SB varied drastically with the peak viscosity obtained, which in turn varied exponentially with the slurry concentration. In several samples of rice flour studied, it was found that not only the magnitudes of BD and SB but even the algebraic sign of SB depended on the slurry concentration chosen. Clearly, viscogram parameters of different samples can be properly compared not at a fixed slurry concentration but only at a fixed peak viscosity. Values of a few ratios at a fixed P value, particularly that of relative breakdown (BD r = BD/(BD + SB)), could effectively differentiate between starch and rice types.