61A-45 |
Water mobility in cassava and potato starches studied by solid-state 2H NMR |
P. CHATAKANONDA1, L. C. Dickinson2, and P. Chinachoti1. (1) Department of Food Science, University of Massachusetts, Amherst, MA 01003, (2) Department of Polymer Science and Engineering, Amherst, MA 01003 Water plays an important role in starch functionality during processing such as heating and freezing. Therefore, water mobility in starch can provide information in fundamental understanding of water dynamics in starch granules. To investigate changes in 2H water mobility in cassava and potato starch during hydration. Cassava (commercial, rainy and drought crops) and potato starch samples were equilibrated over saturated salt solutions (containing D2O) of known water activity (ranging from 0.03-0.97 aw) at 25 oC for 7-10 days to allow equilibration before the NMR analyses. Mobility of water in cassava and potato starches was determined by solid-state NMR as a function of D2O content ranging from 0 to 42% (dry basis). Measurements of relative mobility were based on relative area and line-shape analysis. As D2O content increased from 0%, the signal started to show at 5%, and significantly increased after 10% (accompanied by a line narrowing) indicating an increase in mobile fraction of D2O. Above saturation level (~20% D2O), no more signal change was observed as excess water contributed to extra-granular water. The increase in T2 relaxation times suggested that the molecular mobility reached a fast exchange regime. The same trends were observed in all samples. However, only potato starch showed a pake pattern (a splitting of about 1 kHz) above 24% D2O. This pake pattern may come from anisotropic motion of water. Further investigation will be discussed. Cassava and potato starches represented similar hydration behavior, but their different peak patterns above the water saturation level were observed by 2H solid state NMR. This could greatly influence the functionality of these two starches during processing.
Session 61A, Carbohydrate
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