Effects of Hydrostatic Pressure-Treatment and Allylisothiocyanate Addition on Quality of Grated Yam Soup

For the purpose of development of grated yam (Dioscorea opposita Thunb.) soup with high viscosity and low survival fraction of bacteria, effects of hydrostatic pressure-treatment and addition of allylisothiocyanate (AIT) on the quality of grated yam soup were examined. 1) The viscosity of grated yam dropped with hot water treatments (over 80°C) remarkably. The survival fraction of bacteria did not decrease with hot water treatments of the temperature (under 70°C) that the viscosity of grated yam did not drop. 2) The more AIT that was added, the higher the effect of decrease of bacteria became. The effect of decrease of bacteria was confirmed at AIT 0.005ml/100g. There change of color of the grated yam soup with the addition of AIT under 0.02ml/100g. 3) On the condition of hydrostatic pressure-treatment, the effect of decrease with 700 MPa pressure condition was higher than that with 400 MPa pressure condition. By combining hydrostatic pressure-treatment and the addition of AIT, the survival fraction of bacteria was reduced even more. 4) There was only a slight change of viscosity of grated yam soup with hydrostatic pressure-treatments. However, with 700 MPa pressure condition at 50°C, the viscosity of grated yam soup was reduced. The change of b (yellow) value of color was confirmed with 700 MPa pressure condition. With 700 MPa pressure condition at 20°C or 50°C, b value decreased slightly.