||The characteristics of the currently available enzymes for rice-cooking are investigated. These properties included heat-resistance, abilities to cut amylose and to produce mono-, di-, tri-, and tetrasaccharides. The function of rice-cooking was also evaluated.
First, the ability of the enzyme to produce low-molecular-weight saccharides from starch was determined. Results indicated that the rice soaked in water for 15 minutes without addition of enzyme yielded mono- and disaccharides alone. However, the rice soaked in water in the presence of the enzyme yielded not only more amounts of mono- and disaccharides but also tri- and tetrasaccharides compared to that without enzyme. The increase of mono- and disaccharides enhanced the sweetness of rice. The production of tri- and tetra-saccharides resulted from the cleavage of starch by the enzyme. Therefore, the molecular weights of starch and the viscosity of rice should decrease. The enzyme for rice-cooking posses the following properties: (1) the enzyme activity increased with the increase of temperature in the range of 30~35°C, (2) Inactivation of the enzyme occurred at 60°C, (3) Increase of enzyme activity by ~10% when temperature increased by 10°C, (4) The linear correlation declined as the enzyme reaction was prolonged. Two enzymes, A and B, possessed different heat-resistance. Enzyme A lost 4.5~33% of activity for every increase of 10°C, whereas enzyme B was very stable at the temperature ranged from 30° to 50°C. Although different enzymes for rice-cooking possessed varied heat resistance, these enzymes can be used for improving digestibility, texture and sweetness of cooked rice.