Gelatinization and retrogradation of thermoplastic starch characterized using modulated temperature differential scanning calorimetry
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Starches with varying amylose content, one hydroxypropylated high amylose starch and two thermoplastic starches (pre-gelatinized and with V type crystals) were gelatinized in the presence of added water. Gelatinization was characterized using wide-angle X-ray scattering and modulated temperature differential scanning calorimetry (mT-DSC) with a heat-cool temperature profile. The gelatinization endotherms were recorded in total heat capacity curves that were resolved into storage (reversing) and loss heat capacities, and non-reversing heat capacity curve. The endotherms were mainly of non-reversing nature, with a small contribution from the reversing component. Starch melting is a plasticizer-assisted disruption of crystals and other structures such as starch–lipid complexes and granules. Reversibility was limited since the native amylopectin crystals are rarely recrystallized and starch–lipid complexes do not reform. Recrystallization is predominantly due to subsequent slow formation of V type amylose crystals, with some B type due to recrystallization of amylopectin.
KeywordsBiopolymer Amylose Polymorphism Melting Crystallization Wide-angle X-ray scattering
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