Quantitative Determination of Bound Water By NMR

Abstract

SUMMARY— A Nuclear Magnetic Resonance (NMR) instrument was used to measure the amount of liquid water in a complex colloidal system over a broad temperature range. The bound water content, defined as that which remained liquid at 0°F (−18°C), was 0.29±0.01 g water per g dry solid in case of a wheat flour dough. This value was independent of total moisture content for doughs of the same flour with moisture contents greater than 24.6%. NMR signals indicated that most of this water remained liquid at −58°F (−50°C). This method gives a direct reading of bound water and is nondestructive of sample.

Supercooling in Overwintering Azalea Flower Buds

“…Kuntz and coworkers (10) have used this property to study liquid water in frozen protein solutions. Toledo (30) and Sussman (28) Two series of tests using this procedure were performed: freezing-thawing analysis of whole buds and excised primordia and a cooling rate study on whole buds.…”

Frost and Chilling Injury to Growing Plants

“…Some progress in measurement of bound water appears to be possible, utilizing nuclear magnetic resonance (NMR) spectroscopy. Toledo et al (1968) were able to measure the bound water content of wheat flour dough with good precision, for a given temperature, such as -18°C, regardless of total water content. Considerable progress has already been made in defining protein hydration characteristics at freezing temperatures.…”

“…There is little doubt that biochemical systems contain liquid water at subfreezing temperatures, and that the amount of this bound water (Fig. 2) decreases with temperature (Levitt, 1956;Toledo et al, 1968) and/or with molecular denaturation (Pichel, 1965). Table III) at the ice-water interface under equilibrium conditions.…”

Bound and free water relationships in soy proteins as measured by differential scanning calorimetry

“…The same reasoning as has been applied to the bound water measurements of Kuntz et al (1969) and Toledo et al (1968), applies to Hansen's (1976Hansen's ( ,1978 measurements on soy protein products and ovalbumin. His NMR measurements of • bound water were also based on the assumption that unfreez able (bound) water retains a high degree of mobility.…”

“…Structural heat capacity is attributed to the breakdown of an associated water structure (Berendsen, 1967). Toledo et al (1968) measured bound water in essentially the same way as did Kuntz et al (1969). The wide-line NMR instrument was adjusted so that only water with a high degree of mobility produced a signal.…”