Abstract: Carboxymethyl pullulan-calcium chelate [CMP-Ca (II)] was synthesized by the reaction between water-soluble carboxymethyl pullulan (CMP), prepared from pullulan, and Ca2+ and was structurally characterized by ultraviolet (UV) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Based on the calcium content in CMP-Ca (II) determined by titration, one-factor-at-a-time method and response surface methodology with Box-Behnken Design were used jointly to determine the optimal preparation conditions for CMP-Ca (II). Finally, a Balb/C mouse model of osteoporosis was created to evaluate the efficacy of CMP-Ca (II) as a calcium supplement by measuring bone mass, mineral density and hardness. The results of UV and FTIR showed that carboxyl and hydroxyl groups in CMP chelated with calcium ions. The optimal conditions for preparing CMP-Ca (II) were as follows: Ca2+/CMP mass ratio 2:1, pH 10 and 50 ℃, and the calcium content of CMP-Ca (II) prepared under the optimized conditions was 10.3%. The animal experiment results showed that CMP-Ca (II) was able to improve the bone mass, mineral density and hardness of mice suffering from osteoporosis and reduce serum alkaline phosphatase (ALP) activity, indicating that CMP-Ca (II) could regulate calcium absorption in mice with osteoporosis, relieve osteoporosis and improve bone status. The method for preparing CMP-Ca (II) presented in this study proved to be simple and convenient and could provide a strategy for the development of a new calcium supplement.

Key words: pullulan; carboxymethyl pullulan-calcium complex; calcium supplement; osteoporosis