88C-1 |
The effect of porosity on glass transition measurement |
K. A. ROSS1, O. H. Campanella, and M. R. Okos. (1) Agricultural and Biological Engineering, Purdue University, 1146 ABE, West Lafayette, IN 47907-1146 Texture is considered a key quality parameter determining the acceptability of many porous foods. Dynamic mechanical thermal analysis (DMTA) is commonly employed in food science research as a means of characterizing the textural properties of food materials through measurement of glass transition (Tg). However the effect of porosity and different sample preparation techniques on Tg measurement have not been investigated. The objectives of this study were to compare Tg measurements of identical materials varying only with porosity and to examine the effect of sample preparation technique on Tg measurements. Both starch based extrudates and synthetic polymers with different porosities (i.e. different bulk densities) were tested with DMTA. For comparison, representative samples from the porous specimens were obtained and subjected to one of three methods of Tg determination: 1) ground into a powder and compressed into tablets for testing with DMTA, 2) ground into a powder and tested by differential scanning calorimetry (DSC), and 3) ground into a powder and tested by controlled strain rheometry. Porosity was observed to affect the measurement of the glass transition using DMTA. The extrudate samples containing the lowest porosity exhibited a Tg range 23 C lower than the extrudate samples with the highest porosity. Also, the polymer samples with the lowest porosity showed a Tg range 20 C lower than the polymer samples with the highest porosity. The tablets (no pores) did not show any significant difference in Tg as measured by DMTA nor did the ground samples (no pores) measured by DSC and rheometry. This study shows that porosity affects Tg measurement. Care should be taken when reporting Tg values as porosity may introduce an artifact in Tg measurements using DMTA.
Session 88C, Food Engineering: Physical and Chemical Properties
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