Abstract

AbstractThe molecular mobility of water in corn starch powders (71 to 96% solids) was determined by deuterium (2H) and oxygen‐17 (17O) high‐field Nuclear Magnetic Resonance (NMR) spectroscopy, in deuterium (D2O) and oxygen‐17 enriched water (H217O), respectively. The NMR transverse relaxation rate (R2) was related to both the concentration and activity of water (aw). The concentration plot showed two regions of water mobility; trapped and monolayer water. The water activity plot showed two linear regions of water mobility; Region A, from 0.99 to 0.23 aw, and Region B, from 0.23 to 0.11 aw. The linear relationship in Region A between water mobility, as measured by R2 and water activity is hypothesized to be due to the hydrophobic nature of the starch granules which results in diffusion limited water motion. Relaxation rates for 2H and 17O at high aw were compared with one another and literature data.

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