36D-33 |
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F. ALTAY, Biological Systems Engineering, Univ. of Wisconsin-Madison, 460 Henry Mall, 220 Agricultural Engineering Building, Madison, WI 53706-1533, S. Gunasekaran, Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, 460 Henry Mall, 220 Agricultural Engineering Bldg., Madison, WI 53706-1533, and S. Kasapis, Dept. of Food Science and Nutrition, Sultan Qaboos Univ., College of Agriculture, P.O. Box 34, Al-Khod, 123, Oman. Gelatin is used in the presence of sucrose and glucose syrup in confectionery products. To understand the effect of ingredient concentration on the viscoelastic characteristics of gel matrices at low temperatures, the dynamic rheological parameters of storage modulus (G') and loss modulus (G”) were used. The objectives of this study were to determine the Williams, Landel, and Ferry constants for gelatin gels in a high sugar environment and to apply the free-volume theory by constructing master curves using time-temperature superposition principles. Gel samples were made by mixing different amounts of gelatin (7 and 10%) and sugar mixtures (70 and 73%, containing 1:1 ratio of sucrose and glucose syrup), while maintaining the water level the same for both systems. The values of G' and G” were measured using a dynamic rheometer with a parallel plate (4 cm diameter, 1 mm gap) in the temperature range of 60 oC to -20 oC at 1 rad/s and 1% strain. To perform frequency-sweep tests in the range of 0.1-100 rad/s, cooling runs from 60 oC to -20 oC were interrupted at constant temperature intervals. The WLF constants, C1 0 and C2 0, were calculated as 8.52 and 78.54 for the mixture containing 7% gelatin whereas they were found to be 11.16 and 90.33 for the 10% gelatin system, respectively. The results suggest that increasing gelatin concentration lowered the free volume of the system at the same water and total solids content. The outcome of this study may be used to predict viscoelastic characteristics of gelatin gels with high sugar concentration at the glass transition region.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |