10-3 |
Elevation of wheat starch gelatinization temperature by saccharides of equivalent molecular weight |
T. M. PAESCHKE and S. J. Schmidt. Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, 769 Laurel Ave., Des Plaines, IL 60016 Substitution of alternative saccharides for sucrose such as fructose and corn syrup in baked goods for economic reasons alters the gelatinization temperature of wheat starch. In general, increasing molecular weight of saccharides increases the gelatinization temperature, but saccharides of equivalent molecular weight can elevate the starch gelatinization temperature to different extents. Clearly the elevation effect is not a function of molecular weight alone. We propose that conformation in solution and hydration properties of particular saccharides in water contribute to the elevation effect in addition to molecular weight effects. Our objective was to correlate hydration and conformation in solution data (literature values) for saccharides of equivalent molecular weight in solution with the measured gelatinization temperature of model wheat starch:saccharide:water solutions Three pentoses, five hexoses, and five disaccharides with equivalent molecular weights were mixed in ratios of 1:1:1 and 1:1:2 wheat starch:water:saccharide. The midpoint gelatinization temperatures were determined using a TA Instruments 2920 DSC, scanning at 10°C/minute from 20°C to 120°C. The elevation of starch gelatinization temperature in general followed the order of pentoses< hexoses< disaccharides. Midpoint gelatinization temperatures for starch:water:saccharide solutions were correlated with literature data for hydration numbers, dynamic hydration numbers, number of equatorial hydroxyl groups, and limiting diffusion coefficients. These properties all describe how water interacts with individual saccharides in solution and were found to correlate linearly with the gelatinization temperature. Correlation coefficients of 0.93 to 0.97 and 0.73 to 0.87 were obtained for the 1:1:1 and 1:1:2 starch:saccharide:water mixtures respectively. These results indicate that the elevation of gelatinization temperature by saccharides is not solely a function of molecular weight. Molecular conformation in solution and the interaction between saccharides and water also directly influence the elevation effect. Knowledge of the hydration characteristics of a particular saccharide provides predictive information on the elevation of the starch gelatinization temperature.
Session 10, Carbohydrate: General
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