Abstract: In this paper, calcium-binding collagen polypeptide (CP-Ca) was synthesized by liquid-state reaction between collagen polypeptide prepared in our laboratory from pigskin gelatin and calcium gluconate, and the effect of CP-Ca on improving bone mineral density (BMD) in rats was investigated. Totally 120 female SD rats were equally divided into 10 groups: control group (deionized water by gavage), low-, middle- and high-dosage CP-Ca groups (139.28, 278.55 and 557.10 mg/(100 g·d)), low-, middle- and high-dosage CaCO3 groups (25, 50 and 100 mg/(100 g·d)), and low-, middle- and high-dosage CP + CaCO3 group (139.28 mg /(100 g·d) CP + 25 mg/(100 g·d) CaCO3, 278.55 mg/(100 g·d) CP + 50 mg/(100 g·d) CaCO3, 557.10 mg/(100 g·d) CP + 100 mg/(100 g·d) CaCO3). All rats were fed on a basic diet and deionized water. The body weight and length of the rats were recorded weekly. A three-day calcium metabolism experiment was carried out in the fourth week to estimate the apparent absorptivity of calcium. Serum calcium (SCa), serum phosphorusand (S-P), and alkaline phosphatese (ALP), BMD and bone calcium content were measured. The rat femurs were analyzed by scanning electron microscope (SEM). The results showed that CP-Ca at middle and high dosages and CP + CaCO3 at high dosage could significantly promote body weight gain (P < 0.05), and the effect of CPCa was more apparent. CP-Ca and CP + CaCO3 had obviously lower ALP activity than the control group (P < 0.05). CP-Ca and CP + CaCO3 both at middle and high dosages significantly raised BMD compared to the control group (P < 0.05), and CP-Ca was more effective at the high dosage. At all dosages tested, CP-Ca and CP + CaCO3 resulted in higher Ca bioavailability than CaCO3. CP-Ca could activate osteoblasts on the surface of bones, increase the density of bones and reduce bone calcium loss. Meanwhile, SEM revealed that CP-Ca and CP + CaCO3 could prevent and improve osteoporosis caused by long-term calcium deficiency. CP-Ca was highly soluble, exhibited good dissociation ability, and was rich in calcium and polypeptides so than it can be used in functional foods and health products to prevent osteoporosis and improve BMD.

Key words: pigskin gelatin, calcium-binding collagen polypeptide (CP-Ca), SD rats, bone mineral density (BMD)