The effect of mechanical deformation on the movement of water in foods.
This study has shown the importance of relating NMR spectroscopic information on the water in model food structures to the mechanical properties of those structures. Analysis of the NMR relaxation data can be used to examine the distribution of water domain sizes, and this has been related to the mechanical properties of the samples. A novel NMR probe-head has been designed, which allows both the NMR and the mechanical data to be simultaneously measured during compression of the sample. This probe-head allows compressive stress/strain data to be obtained directly from the NMR sample, allowing changes in the distribution of the water to be directly correlated to changes in mechanical properties.
Gel Characteristics—Waterbinding Properties of Blood Plasma Gels and Methodological Aspects on the Waterbinding of Gel Systems
A methodological study on the waterbinding properties of protein gels was made, where two tests were evaluated. Only one of them, the “net test,” was found useful for work on protein gels. The moisture loss of blood plasma gels was then studied as a function of heating temperature, heating time, pH, protein concentration, and sodium chloride concentration. It was finally demonstrated that a change in the gel structure may affect waterbinding and texture characteristics differently, and these properties should therefore be treated separately when evaluating protein gels. It was, e.g., shown that blood plasma gels became firmer with increasing heating temperature from 72 – 92°C, whereas the waterbinding properties became poorer at temperatures above 77°C and had an optimum at 75 – 77°C.
MEASUREMENT OF GEL WATER‐BINDING CAPACITY BY CAPILLARY SUCTION POTENTIAL
A new simple method has been developed which may be applicable in the measurement of the water-binding capacity (WBC) of moist foods and gels which easily deform under pressure. This study was designed to establish the procedure conditions using gels. The material to be measured is placed in a special cup, layered with filter paper of a predetermined moisture content and held at 6°C for 72 hr. From the change in moisture content of the filter paper after equilibration, the suction potential in N/m2 of the measured material is read off a standard curve. This curve was prepared by measuring the water lost from filter paper in a standard soil test cell as a function of applied pressure. On this basis, the suction pressure as a function of moisture content can be determined at very high water contents.