EXAMINATION OF THE CRYSTALLINITY OF FOOD GELS BY X‐RAY DIFFRACTION

Abstract

ABSTRACTVarious concentrations of agar, carrageenan, and gelatin gels made by adsorption and desorption processes were examined for evidence of crystallinity by x‐ray diffraction methods in an attempt to correlate this with a measure of water binding. As an approach to quantify the degree of crystallinity, the diffraction photographs were also measured for the amount of adsorbed light using a general purpose densitometer, and for the amount of reflected light using a computerized digitizer and false coloring program. Only an amorphous phase was found in the unstressed desorption gels, indicating that the hypothesis of a high degree of oriented crystalline regions forming a capillary‐like matrix is not representative of the true nature of a dilute gel and thus water binding can be based on water‐water and water‐solute interactions alone. Adsorption gels of carrageenan did show a higher degree of crystallinity in the intermediate water activity range. It is suggested that the thermal and mechanical stress during preparation forced the helices to orient into a capillary network. Densitometer scans were unsuccessful in measuring the degree of order in the gel systems as compared to visual observation of the film.