Abstract:In order to reduce the environmental pollution and resource waste of discarded crayfish shells, crayfish shells and D-gluconic acid solution with 50% mass fraction were used as raw materials to prepare human calcium supplement, i.e., calcium gluconate, by ultrasonic-assisted method. The effects of particle size of crayfish shell powder, gluconic acid amount, liquid-to-material ratio, ultrasonic time, reaction temperature and ultrasonic power on the yield of calcium gluconate were studied. The response surface experiment was optimized based on the single factor experiment. The results showed that the optimal process conditions were 4.68 mL of 50 % D-gluconic acid, 30∶1 of liquid-to-material ratio, and 32.1 min of ultrasonication under 45 ℃. The yield of calcium gluconate was 86.38%, which was close to the predicted value of 86.85%. Compared with other non-ultrasonic assisted preparation methods, this yield was increased by 10%. Ultrasonic assistance could increase the yield of calcium gluconate prepared from crayfish shells, and the yield of ultra-finely pulverized crayfish shell powder increased by 3.28% compared with that of the crude crayfish shell powder. The solubility of prepared calcium gluconate at different pH values was much higher than that of the calcium in crayfish shells, with higher absorption and utilization rate, providing the possibility for further use as a human calcium supplement. Crayfish shells were used as a calcium source to prepare calcium gluconate, which could improve the comprehensive utilization of crayfish shells and provide technical reference for reducing environmental pollution and achieving cleaner production.
