Molecular behavior of water in a flour-water baked model system

The molecular behavior of water in complex food systems, via bonding and solvation reactions with low molecular weight solutes or high molecular weight macromolecules, is intimately linked with both the palatability and storage stability of those systems. Due to the difficulty in interpreting data derived from multicomponent finished food products, water behavior in a baked flour-water "matzo" model system was studied. Water behavior was assessed from high resolution [1H] nuclear magnetic resonance (NMR) spin-spin relaxation studies and differential scanning calorimetric (DSC) measurements of unfreezable water content. The unfreezable water capacity of "matzo" model crackers, as measured by DSC, ranged from ca. 24-30% (w/w). These results were corroborated by NMR data. Only one exponent (less than 0.46 msec greater than) is required to fit spin-echo evolution curves below a total moisture content of ca. 20% (w/w), whereas two exponents (less than 0.46 greater than and 1.6 msec) are observed when the moisture content exceeds 20% (w/w). Expert sensory texture assessments parallel unfreezable (= total) water contents between 2.9% (w/w) and 20.1% (w/w). This relationship may be explained by the known tendency for water to plasticize biological polymers, e.g. wheat starch and proteins, and to render these macromolecules incrementally more mobile with increasing water concentration. The similarities (if any) between water of plasticization, immobile water, and "bound" water are discussed, in terms of theoretical physicochemical "states" of water and the various techniques utilized to assess (define) those "states."