Molecular Characterization around a Glassy Transition of Starch Using 1H Cross-Relaxation Nuclear Magnetic Resonance

The aim of this work was to characterize the glassy-rubbery transition in starch gels using molecular (NMR) techniques. Proton cross-relaxation ( 1 H CR) NMR spectra of gelatinized starch (∼50% mc) were obtained by cooling stepwise from 20 to -30 °C. A significant line broadening was observed in the CR spectra between 0 and -10 °C. Deconvolution of the spectra into its component curves (broad and narrow) yielded a peak amplitude, width at half-height, and peak area for each curve. Between 0 and -10 °C (temperatures around Tg), a significant line width change in the broad component (rigid solid) was apparent. These observed qualitative changes may be evidence of a glassy-rubbery transition at a molecular (short-range) level which are strengthened by a similar transition temperature range found previously with 13 C CP-MAS and DMA tan δ(T) measurements. However, the increase in the relative quantity of rigid protons observed by 1 H CR NMR spectra could also be attributed to ice. The 1 H 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.