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A calcium-binding peptide was successfully purified from tilapia (Oreochromis niloticus) scale protein hydrolysate by hydroxylapatite affinity (HA), gel filtration and reverse phase high-performance liquid chromatography (RP-HPLC). This peptide was sequenced as DGDDGEAGKIG (N- to C-terminal, MW = 1033 Da) based on MALDI-TOF-MS/MS. There was no significant difference in body weight gain, serum P content or alkaline phosphatase (ALP) level in Ca-deficient rats after supplementation with TSPH–Ca (tilapia scale protein hydrolysate calcium complex), CPP–Ca (casein phosphopeptide calcium complex), CaCO3 or saline (control). However, the apparent absorptivity of calcium, serum and femur Ca content, femur bone mineral density and strength in the rats fed with TSPH–Ca were significantly higher than those of rats in the control and CaCO3 groups (P 0.05), indicating that TSPH possesses the potential to serve as an alternative for CPP.

Carp egg phosphopeptide (EPP) with Ca binding activity was isolated from tryptic hydrolysate by ultrafiltration and hydroxylapatite chromatography. EPP mainly consists of 3.99 ± 0.12% P (w/w) and 20.36 ± 0.50% serine residues (w/w). In vitro EPP exhibited high Ca binding ability which was slightly lower than that of casein phosphopeptide (CPP) and could inhibit the formation of insoluble Ca salts. In vivo the effects of EPP on increasing Ca bioavailability were further studied in Ca-deficiency rats. All rats were randomly divided into five groups, one group served as the normal group to feed with a normal-Ca diet including CaCO3 for 8 weeks, another as the Ca-deficiency group to feed with a low-Ca diet for 8 weeks, the other three groups to feed with the low-Ca diet for 4 weeks and then randomly assigned to the control group and two experimental groups. The control group was switched to the normal-Ca diet for 4 weeks. The experimental groups were fed with the normal-Ca diet containing EPP and CPP for 4 weeks respectively (marked as the EPP group and CPP group). During the experimental period, Ca absorption and its accumulation in bone was significantly increased by EPP supplementation. The levels of serum Ca, bone mineral density, bone Ca content and biomechanical properties of the EPP group were significantly higher than those of control group (p < 0.05), but similar to the CPP group (p > 0.05). EPP is expected to become a novel Ca nutraceutical additive in food industry due to enhancing Ca bioavailability by its intake. [ABSTRACT FROM AUTHOR]