Molecular characterization around a glassy transition of starch using H-1 cross-relaxation nuclear magnetic resonance

The aim of this work was to characterize the glassy-rubbery transition in s tarch gels using molecular (NMR) techniques. Proton cross-relaxation (H-1 C R) NMR spectra of gelatinized starch (similar to 50% mc) were obtained by c ooling stepwise from 20 to -30 degreesC. A significant line broadening was observed in the CR spectra between 0 and -10 degreesC. Deconvolution of the spectra into it's component curves (broad and narrow) yielded a peak ampli tude, width at half-height, and peak area for each curve. Between 0 and -10 degreesC (temperatures around T-g), a significant line width change in the broad component (rigid solid) was apparent. These observed qualitative cha nges may be evidence of a glassy-rubbery transition at a molecular (short-r ange) level which are strengthened by a similar transition temperature rang e found previously with C-13 CP-MAS and DMA tan delta>(*) over bar * (T) me asurements. However the increase in the relative quantity of rigid;protons observed by H-1 CR NMR spectra could also be attributed to ice. The H-1 CR NMR method showed its potential application for probing solid components in gels using a simple and economical NMR spectrometer, without the need for a solid-state instrument.