Bound Water Defined and Determined at Constant Temperature by Wide‐line NMR

SUMMARY The purpose of this work was to study the NMR properties of bound water (BW) in wheat flour, corn starch and egg white at room temperature end to develop a method for quantitative determination of BW in a material and its maximum BW capacity. Each sample was studied over the 5 to 85% moisture range, using a wide‐line NMR Spectrometer. At the lowest radiofrequency attenuation, hydrogen nuclei from free water gave a negligible signal but the hydrogen from BW gave a strong signal, giving rise to a new definition for BW and a new method for its quantitative determination, both at room temperature. Within a given set of instrument parameters, the hydrogen nuclei from BW showed NMR properties independent of dry matter. Therefore, a “universal” NMR calibration constant per unit weight BW could be derived for these food products. The weight of bound water per unit weight of dry matter increased with increasing total moisture content to a maximum, called Bound Water Capacity, which was independent of total moisture content but varied with the product.