COMPLEX MELTING OF SEMICRYSTALLINE CHICORY (CICHORIUM-INTYBUS L) ROOTINULIN

When concentrated solutions (30-45% by weight) of inulin (degree of po lymerization 2-66, number average degree of polymerization 12) are coo led at 1 degrees C/min or 0.25 degrees C/min from 96 degrees C to 20 d egrees C, suspensions of semi-crystalline material in water are formed . A thermal nucleation process was detected by optical microscopy: the 8-like shaped crystallites resulting from primary nucleation at highe r temperature are larger than those resulting from secondary nucleatio n at lower temperature. Differential scanning calorimetry (DSC) thermo grams display melting profiles with three to four partly overlapping e ndotherms that vary as a function of concentration, cooling rate durin g crystallization and storage time at 25 degrees C of the crystallite suspension. Recrystallization during melting was observed. The wide-an gle X-ray scattering patterns of the samples at 25 degrees C correspon d to those of the hydrated crystal polymorph. The structural changes d uring melting indicated the existence of a single crystal polymorph th roughout melting. A periodicity of 95 Angstrom, arising from alternati ng regions of different electron density, is detected in the small ang le X-ray scattering patterns at 25 degrees C. The stepwise increase of the long period upon heating is related to the existence of two types of lamellar stacks: one with a higher long period, resulting from the primary nucleation and thus crystallized at high temperature, and a s econd one with a smaller long period, formed by crystallization at low er temperature. The lamellae formed at low temperature melt at a lower temperature than those formed at high temperature, explaining the exi stence of the two DSC-endotherms. (C) 1998 Elsevier Science Ltd. All r ights reserved.