| Eggshell is a kind of natural green biological calcium source.There are about 4million tons of discarded eggshell every year in China,which not only causes environmental pollution,but also wastes resources.In this study,using eggshell as raw material,the inorganic calcium in eggshell was transformed into organic calcium such as calcium gluconate,calcium lactate,calcium acetate and calcium citrate by direct neutralization method,and the process was optimized by response surface method;the biological conversion rate of organic calcium was determined by animal test,in order to provide a safe and feasible technical basis for the comprehensive utilization of eggshell.(1)Study on the preparation of calcium gluconate from eggshell.50 % gluconic acid was prepared from food grade gluconic acid-?-lactone and reacted with pretreated eggshell under certain water bath temperature and time.On the basis of determining single factor,four factor and three level design of response surface box Behnken was adopted.The optimum technological conditions for the preparation of calcium gluconate from eggshell were as follows: under the conditions of 3 g eggshell powder,32 mL of 50 % gluconic acid,1:12 solid-liquid ratio,30 ? reaction temperature and 1 hour reaction time,the highest yield of calcium gluconate can reach10.31 g.(2)Study on the preparation of calcium lactate from eggshell.Calcium lactate was prepared by neutralization method,and the factors such as reaction temperature,reaction time,amount of lactate and solid-liquid ratio were set to influence the yield.The optimum conditions for the preparation of calcium lactate from eggshell were determined by the response surface box Behnken four factor three level design according to the interaction of each factor: the highest yield of calcium lactate was5.35 g when the amount of lactate was 7 mL,solid-liquid ratio was 1:16,reaction temperature was 45 ?,reaction time was 90 min.(3)Study on the technology of calcium acetate to calcium citrate from eggshell.Using two-step neutralization method,calcium acetate was first prepared.Through the single factor test to determine the amount of acid,solid-liquid ratio,reaction temperature and time,and using the response surface box Behnken four factor three level design,the best technological parameters for the preparation ofcalcium acetate were determined as follows: egg shell powder 3 g,solid-liquid ratio1:16,acetic acid dosage 6 mL,reaction temperature 20 ?,reaction time 75 min.Then,the optimal conditions for the conversion of calcium acetate to calcium citrate were as follows: over 20 % citric acid reacts with calcium acetate,the temperature of water bath is 80 ?,the reaction time is 5 hours,and the highest yield of calcium citrate is3.02 g.(4)Study on bioavailability of four kinds of organic calcium.Calcium gluconate,calcium lactate,calcium acetate and calcium citrate were respectively made into honey pills.Mice were selected for animal experiments to determine the apparent absorption rate and growth change.The calcium content in faeces,urine and femur calcium was determined by inductively coupled plasma mass spectrometry(ICP-MS)and inductively coupled plasma spectroscopy(ICP-OES).The results showed that the organic calcium extracted from the eggshell had a significant effect on the calcium absorption of mice(P<0.05).The organic calcium given 66.5 mg/kg per day(calculated by calcium content and mouse weight)could significantly improve the bone calcium level of mice and promote the normal growth of mice.The absorption effect is better than that of calcium carbonate with the same calcium content.SPSS analysis of variance showed that the order of the influence of four kinds of organic calcium on the absorption and utilization of mice was: D>F>C>E,that is,calcium gluconate group>calcium citrate group>calcium lactate group>calcium acetate group.According to the significance analysis,calcium organic acid can promote the absorption of mice more than calcium carbonate. |
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