GLASS-TRANSITION TEMPERATURES DETERMINED USING A TEMPERATURE-CYCLING DIFFERENTIAL SCANNING CALORIMETER

Glass transition temperatures, T-g, of polystyrene, polyvinylpyrrolido ne, polydextrose, gelatin, corn flakes, pasta, and aqueous glucose/gly cine solutions were determined using a differential scanning calorimet er which cycled the temperature while the net temperature increased at a constant rate. Operating conditions of the modulated differential s canning calorimeter(TM) (MDSC(TM)) for optimizing the endothermic base line shift associated with the glass transition were a scan rate of 5 degrees C/min with an amplitude of +/- 1 degrees C over a modulation p eriod of 60 or 100 sec. The MDSC successfully separated the glass tran sition from other irreversible thermal changes in simple food ingredie nts. While the MDSC did not distinctly determine T-g of complex food s ystems at low moisture contents, glass transitions were observed for s olutions and food systems at higher moisture contents. T-g values from MDSC were reproducible and similar to those from standard DSC.