Abstract
A variety of phase transitions occurring in food ingredients during heating were observed with plastic fat and fat emulsion, hydrogels of agar and gelatin, egg white, yolk and their mixture, and aqueous suspensions of potato, rice and corn starches. Measurements were also made to obtain informations on the modulus of instantaneous elasticity of all the samples as a function of temperature in a range from about 30°C to 90°C. In the course of heating, the increasing curves of temperature in fats and hydrogels descended pronouncedly by endothermic behaviour due to their melting or gel-sol transition. The elasticity of these samples also decreased abruptly at around the temperature of transitions described above. A rough shape in the increasing curves of temperature was observed in the egg components.This may have been due to the response from the thermal coagulation ingredients in eggs in a wide range of temperature. The elasticity of yolk and of the whole mixture of egg components was higher than that of egg white above 65°C. Gelatinization of starches in an aqueous medium during heating did not react apparently to the increasing curve of temperature, while such a smooth curve for each starch sample conformed to the exponential equation reported. This may also have been brought about by an extent of starch gelatinization over a wide range of temperature. The gelatinized rice and corn starch samples indicated a maximum value of elasticity at around 80°C corresponding to the disappearance of a crystal region in each type of starch granule.
