Starch in rubbery and glassy states by FTIR spectroscopy

The organization of various starch samples varying in molecular structure, organization and moisture content was studied by ATR-FTIR spectroscopy. The comparison of the infrared spectra showed that band intensities in the 1065–870 cm−1 region can be explained by their mobility related to the glass transition, Tg, which occurs at room temperature in the 15–21% water content range. Spectra analyzed using principal component analysis showed main structure/moisture changes for the 1000/1022 cm−1 intensity ratio. The helix organization at a short order range was weakly moisture dependant below Tg, whereas the signal became increasingly water dependant with the crystalline/amorphous ratio above Tg. This result is in agreement with the model of liquid crystal structure and mesophase variation: water allows the self-assembly of amylopectin helices leading to layered organized structure.