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Résumé :
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The retrogradation and physical ageing of model starch systems with respect to their glass transition temperatures T-g have been investigated by Fourier transform infrared spectroscopy and solid state NMR spectroscopy. Diffuse reflectance Fourier transform infrared (DRIFT) spectra demonstrate the commencing retrogradation of starch materials stored above their T-g by changes in peak lineshapes and intensities in the characteristic area between 995 cm(-1) and 1020 cm(-1). Solid state NMR proton relaxation times in the rotating frame (proton T-1 rho) show a characteristic course in relation to the storage conditions (time, humidity), for a which a distinction is made between physical ageing which occurs below the T-g, and recrystallisation (retrogradation) which takes place above T-g. The proton T-1 rho's of materials 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 further water absorption and then increase due to recrystallisation (retrogradation).
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