Macro- and Microscopic Observations on the Phase Tansitions Occurring in Food Ingredients during Heating

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1) Many of the food ingredients exhibit phase transitions accompanying with exo- orendothermic heat during cooking, A series of experimental studies were made to clarify the effectof such the phase transitions, on the increasing curve of temperature in foods under the definite condition of heating procedure so as to formuhze thermal conduction in the foodstuffs.2) As far as the macroscopic examinations are concerned, two different types >of measurements were made to obtain informations on the increasing temperature along by the one dimensional axis from the heating plane and on the changes in elasticity in oleo-systems, aqueous gels of agar and gelatin, aqueous suspensions of starch granules (provided from potato,rice and corn), and egg systems (egg yolk, white and their mixtures), so that it waspossible to examine the effect of oleo-phase melting, gel-sol transition, starch gelatinization, and thermal denaturation of proteins on the respective increasing curves of temperature. The res … More ults obtained suggested that the increasing curve of temperature is not influenced by the gelatinization of starch granules, while the curve goes down temporarily for the cases of melting in oleo-systems and sol transition in aqueous hydro-gels. Somewhat of a complex pattern was observed in the increasing curves of temperature in the egg systems because of the various thermo-sensitive components existing in egg. Consequently, two or more formulae are necessary for describing thermal conduction in the foodstuffs during heating. The changes in mechanical properties of the above systems appear rather simply when phase transitions occur in each ingredient, while each value of the elasticity was characterized by the phase components in the systems to be examined.3) In view of the microscopis examination on the phase transitions, an attempt was made to observe the gelatinization of potato starch, thermal denaturation of egg proteins and sol transition of aqueous agar gel using an optical microscope possessing a thermo-controlled sample-cell and a videoized visual system. Although it could be visualized swelling and gelatinization of starch granules, there were some difficulties for marking egg proteins and aqueous agar gel within the range of microscope. It is, therefore, necessary to continue improvements of the optical systems and the preparation techniques for visualizing phase transition with the various ingredients. Less