Phase change in amylose-water mixtures as seen by Fourier transform infrared

The phase content of amylose-water mixtures (0.7/0.3 w/w) has been analysed by transmission Fourier transform infrared (FTIR) spectroscopy in the 1175 -950 cm(-1) region. Spectra are obtained under three different conditions: in) as a function of temperature (T) from 25 to 97 degreesC; (b) at room te mperature (RT), after slou cycles of T: and (ci at RT after quenching. T-ma x, the maximum temperature in the cycle, ranges from 50 to 120 degreesC. Th e quality of the seven-bund spectra allows for an unambiguous determination of each band area. Unexpectedly, slow cooling after different T-max brings about wide changes in the spectra while quenching does nor. Two jumps in t he absorbance are found: one at 70 degreesC and the other above 105 degrees C. Previous work on slow calorimetry of amylose-water mixtures suggests tha t these temperatures correspond to the beginning and the end of the same ph ysical phenomena that takes place slowly between these two temprtatures-nam ely the dissolution of the strained network phase. The spectra have two dis tinct regions, the low warenumber region (1078-950 cm(-1)) and the high war enumber region (1175-1078 cm(-1)). A distinct gain in the integrated absorb ance of the 1175-1078 cm(-1) region at the expanse of that of the 1078-950 cm(-1) region when T-max increases is interpreted as a change from strained to unstrained environments. A nonequilibrium state between the chains is a strained environment. In light of the C-13 NMR evaluation of the change of molecular order with T, the observed changes of the ir spectra could corre spond to a transformation of a network of double helices into freer chains, possibly single helices. The present in-depth analysis of equilibrium or n ear equilibrium stales by FTIR can serve to understand, through in situ spe ctra. molecular mechanisms during the gelation/crystallization of amylose a nd other gel-forming polymers. (C) 2001 John Wiley & Sons, Inc.