The glass transition and the sub-T-g endotherm of amorphous and native potato starch at low moisture content

The glass transition temperature (T-g) of amorphous and native potato starch with 16% moisture was investigated by means of DSC. The glass transition in amorphous potato starch could be observed in a rescan of native potato starch, after heating to 210 degrees C and quenching. The T-g-onset was 40 degrees C, in agreement with literature data. The T-g of native potato starch is partly obscured by a so-called sub-T-g endotherm. It was demonstrated by means of aging experiments that this endotherm is related to enthalpy relaxation rather than to carbohydrate-water interactions. After erasing the thermal history of the sample by a short treatment at 90 degrees C, a distinct glass transition with an onset at 80 degrees C was observed. This was confirmed by additional aging and annealing experiments. (C) 1997 Elsevier Science Ltd.