Food hydrocolloids are sold as powders so they must be dissolved before use
. In modem manufacturing practice, rapid dissolution can be an important sp
ecification. However, quantifying dissolution kinetics is a problem, becaus
e when lumps form the process becomes irreproducible, partly because lumps
tend to stick to the stirrer. This paper presents a simple method for deter
mining the dissolution kinetics of soluble polymer powders which solves the
se problems. The dissolution kinetics were followed using a modified rotati
onal viscometer. The key modification is that when the powder is added, the
re is a vortex below the axis of the rotor, so that the powder cannot stick
to it. The amount of hydrocolloid dissolved is followed via the torque on
the viscometer. Measurements were performed under both dispersing and non-d
ispersing conditions. Under dispersing conditions each powder grain dissolv
es individually, and it is shown that the dissolution rate is proportional
to the amount of powder surface. Under non-dispersing conditions, grains ca
n stick together, forming lumps. The reproducibility of the method under bo
th conditions is demonstrated using pectin. It was used to quantify the emp
irical observation that reducing the powder grain size increases the dissol
ution rate, but it also greatly increases lump formation. (C) 1999 Elsevier
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