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T. LABUZA, Department of Food Science & Nutrition, University of Minnesota, 136 ABLMS, St Paul, Minneapolis, MN 55108

The work supported by the Marcel Loncin Prize was focused on the application of glass transition state principles to practical problems involved in the processing and storage of carbohydrate based food systems. Of critical importance is the obtaining of the glass transition temperature (Tg) as a function of moisture content of the system in the form of a semi-empirical state diagram. Current researchers have used a variety of methods and have usually not done replicates. Thus a number of methods were used (DSC,DMA, DMTA, NMR) for several carbohydrate polymers or processed cereal products. It was found that each method gives a different curve and that the difference in Tg of replicates can be large. This suggests that food systems are fairly heterogeneous and that each method is measuring a slightly different regime, thus in a sense there is no one Tg value at any given moisture content and any correlation of a physical phenomenon directly to a single Tg curve may be fortuitous. The main thrust of this study was to chose one cookie system and try to determine if there was a one to one correlation between the loss of sensory crispness and the Tg vs. moisture curve in spite of the first findings. To do this a new experimental sensory design test and training was developed. Our results showed such a correlation exists but it is tenuous given the variability in Tg measurement. Of importance is that the brittle/ductile transition curve can also explain sensory crispness. In a second study we determined the influence of moisture on popping volume of popcorn. Popped volume more than doubled as the aw of the corn increased from 0.11 to 0.75, then decreased. Although Tg only slightly changed up to 0.75 aw and dropped at0.8, there was a significant change in the D Cp over this range especially for the pericarp. How these influence the large change in popped volume will be speculated on. Progress on other Tg related studies will be reviewed including a cotton candy state diagram comparison between trehalose and sucrose and the measurement of the change in reactant diffusivity as influenced by non-water plasticizers (glycols) with respect to the state diagram.