It was observed, through differential scanning
calorimetry, that glycerol behaves as an “antiplasticiser”
as it hinders the gelatinisation process
rather than assisting it. It is proposed that in starchglycerol
mixtures, the hydrophilic nature of glycerol
interferes with the moisture uptake of starch, and
hence diminishes the effective moisture contents of
the starch available to aid gelatinisation. This
hypothesis was tested through sorption studies
comparing the rate of moisture absorption of starch,
glycerol and mixtures thereof. The Peleg model
was fitted to the sorption data to predict the effective
amount of water available to the starch in starchwater-glycerol
mixtures.
It was shown that the gelatinisation temperature of
the starch-glycerol-water mixtures was equivalent to
that of starch-water mixtures with the calculated
effective moisture content. Thus it was shown that
the gelatinisation temperature of starch-glycerolwater
mixtures can be predicted based on sorption
behaviour of the ingredients.
The method presented here may be applicable to a
wider range of starch mixtures. This method may
also be used to control the gelatinisation process,
by compensating for the hygroscopic nature of the
various ingredients by altering the total moisture
added.