EXAMINATION OF STARCH-WATER AND CELLULOSE-WATER INTERACTIONS WITH NEAR-INFRARED (NIR) DIFFUSE REFLECTANCE SPECTROSCOPY

Starch-water and cellulose-water interactions were examined with NIR diffuse reflectance spectroscopy. Samples of native potato, wheat, and corn starches and microcrystalline cellulose (MCC) were equilibrated to water activities (a(w)) ranging from 0.11 to 0.94 a(w). A modified B.E.T. model was applied to the water vapor sorption isotherm (T = 25-degrees-C) data. NIR spectra (1000 to 2640 nm) revealed no abrupt changes in molecular structure. However, as has been suggested in the literature, there appear to be two species of non-freezable water whose relative quantities change as a(w) varies. It is hypothesized that the first species represents water within the monolayer, and the second species represents multilayer water. NIR spectra of starch suggests that some multilayer water is present before the monolayer is completed. Spectra of MCC corroborate the existence of two species of highly associated water. The isotherm model was highly successful in describing sorption behavior over the a(w) range examined.