The effect of starch microstructure on glass transition, gelatinization, and the elevation of the gelatinization temperature by saccharides

The microstructure of ungelatinized starch and non-uniform distribution of water was examined as the source of enigmatic behavior of starch during thermodynamic transitions, such as glass transition, starch gelatinization, physical aging, and the elevation of the starch gelatinization temperature by saccharides.; Modulated differential scanning calorimetry (MDSC) was used in an attempt to separate the glass transition from the starch gelatinization temperature. Amplitude, oscillation period and heating rate for the MDSC analysis were optimized to insure equilibrium heat transfer between the DSC and the sample. The optimized conditions for the MDSC analysis did not show a glass transition before gelatinization. This does not preclude the existence of a glass transition immediately preceding gelatinization, only that it is not measurable with the MDSC methods used.; Physical aging phenomenon was also examined by equilibration of starch at specific relative humidities in a dynamic vapor sorption instrument (DVS) with subsequent analysis using standard and MSDC. No evidence was found to attribute physical aging to the V_h conformation comparing ungelatinized versus gelatinized corn or wheat starches or among mutant corn starch varieties (high amylose, native, and waxy). The lack of definite conclusions was attributed to the irreproducibility and high variability in the data.; The elevation of the starch gelatinization temperature in wheat starch and water solutions by saccharides was examined using standard DSC and the data was correlated with hydration information for saccharides from the literature. The hydration characteristics and how a saccharide stabilizes the structure of water were highly correlated to the elevation effect. Regression of molecular weight with the elevated starch gelatinization temperature for a total of 26 mono-, di-, and oligosaccharides did not produce strong correlations, indicating that molecular weight is not a good predictor of the elevation effect.; The microstructure of starch and non-uniform distribution of water within starch granules affect how starch granules interact with water which in turn governs the magnitude, energy, and temperature of subsequent thermodynamic transitions.