The Effects of Preparation Conditions on the Physical Properties and Microstructure of Gomatofu

Abstract

The effects of mixing rates (60, 150, 250, 350 rpm) and the cooking times (15, 25, 35, 45 min) on the physical properties of gomatofu (sesame tofu) were studied by using a rheometer and a scanning electron microscope (SEM). Gomatofu was prepared using two different kinds of cooking methods: the usual system A (simmering) and B (hot-water-dropping into cookpot to hold a constant quantity during cooking) were employed. A creep curve for the gomatofu could be analyzed by using a 4-element model. Hardness and elasticity of Hookean and Voigt body (E0, Ei) of the (A) sample cooked for 25 min decreased with mixing time for all of the samples under various mixing rates, and after 25 min of cooking increased with cooking time because of weight loss. Adhesiveness and viscosity of the Newtonian and the Voigt bodies (ŋN, ŋi) of the sample mixed at 60 rpm increased with cooking time, while both of the samples mixed at 250 rpm and 350 rpm decreased with cooking time. Hardness, adhesiveness and gumminess of the (B) sample for all mixing rates decreased exponentially with an increase of cooking time, but cohesiveness did not change in all of the cooking times. Adhesiveness showed different changes among mixing rates. SEM observations revealed that the sample cooked with a mixing rate of 60 rpm for 15 min did not have a honeycomb structure, while the sample cooked with the mixing rate of 250 rpm for 25 min had uniform-sized cells and a honeycomb structure. It is assumed that gomatofu is a phase separated model which has networks consisting of Kuzu starch and sesame protein. © 1995, Japanese Society for Food Science and Technology. All rights reserved.