Abstract: The first purpose of this research was to study the properties of ultra-fine eggshell powder in comparison with those of coarse eggshell powder. A second purpose was to optimize the preparation of calcium-chelating glutamate from ultra-fine eggshell powder using combination of one-factor-at-a-time method and response surface methodology. Results showed that the filling property, water solubility and electric conductivity of ultra-fine eggshell powder were better than those of coarse powder and a pulverization time of 4 min was found to be optimal to achieve the best quality of ultra-fine eggshell powder. Calcium-chelating glutamate prepared from ultra-fine eggshell powder demonstrated an increase in chelating rate of 12.57% compared with that prepared from coarse powder. Ultra-fine pulverization improved the utilization rate of glutamic acid and simultaneously cut down energy consumption. The optimal conditions for producing calcium-chelating glutamate were determined as follows: molar ratio of eggshell powder to glutamic acid, 1:2.0; pH, 7; chelating time, 59 min; and chelating temperature, 60 ℃. Under these optimal conditions, the chelating rate of calcium-chelating glutamate was 81.12%.

Key words: ultra-fine pulverization, eggshells, properties of powder, calcium-chelating glutamate, chelating rate