Ageing of starch based systems as observed with FT-IR and solid state NMR spectroscopy

The retrogradation and physical ageing of model starch systems with respect to their glass transition temperatures T-g have been investigated by Fouri er transform infrared spectroscopy and solid state NMR spectroscopy. Diffus e reflectance Fourier transform infrared (DRIFT) spectra demonstrate the co mmencing retrogradation of starch materials stored above their T-g by chang es in peak lineshapes and intensities in the characteristic area between 99 5 cm(-1) and 1020 cm(-1). Solid state NMR proton relaxation times in the ro tating frame (proton T-1 rho) show a characteristic course in relation to t he storage conditions (time, humidity), for a which a distinction is made b etween physical ageing which occurs below the T-g, and recrystallisation (r etrogradation) which takes place above T-g. The proton T-1 rho's of materia ls stored below T-g increase asymptotically in time due to physical ageing, whereas the proton T-1 rho's of materials stored above T-g increase until a moisture content is reached that rises them above T-g, decrease due to fu rther water absorption and then increase due to recrystallisation (retrogra dation).