Preparation and physicochemical characteristics of fish collagen peptide chelated calcium by high-energy wet ball milling

Calcium is an essential mineral for human body. Deficiency of calcium leads to osteoporosis, even induces diseases such as hypertension, diabetes and kidney stones. The common calcium supplements found on the market include calcium acetate, calcium lactate and calcium gluconate. Calcium concentrations of these calcium supplements are high, while bioavailability is low. It has been reported that the collagen peptide chelated calcium has the characteristics of high stability, strong anti-interference ability, and high bioavailability. In this study, fish collagen peptide and CaCl₂ were physically milled with a high-energy wet ball mill, in order to develop new production process of collagen peptide chelated calcium. The techniques including FT-IR infrared spectrum, X-diffraction and EDS energy spectrum, were used to analyze physicochemical properties and structure of the collagen peptide chelated calcium. As the milling time was extended from 15 to 240 min, the particle size of the mixture showed an approximately normal distribution and the average particle size of fish collagen peptides gradually decreased from 872 to 343 nm. The absolute value of ZETA potential gradually increased from 3 to 11 mV. The proportion of molecular weights in the <500 u range decreased from 55.806% to 35.999%, that in the 500-1 000 u range increased from 19.178% to 27.031%, that in the 1 000-3 000 u range increased from 21.672% to 30.539%, and that in the >3 000 u range increased from 4.344% to 5.981%. pH value gradually increased from 6.34 to 8.75. The calcium chelation rate gradually increased from 74.21% to 85.42%. The chemical structure of fish collagen peptide chelated calcium was similar to that of fish collagen peptide. However, -COO⁻¹ V_AS absorption peak (1 643.89 cm⁻¹) of collagen peptide moved to 1 540-1 555 cm⁻¹ (shorter wave number) after milling, and the characteristic absorption peak of -NH₂(3 313.9 cm⁻¹) shifted to 3 337.12-3 380.59 cm⁻¹ (longer wave number). The characteristic broad fish collagen absorption peak located at 2 θ=20° disappeared after milling, while multiple sharp peaks (including 2 θ=26, 28, 48 and 58°) and dispersion peaks appeared, indicating that it changed from amorphous to both crystalline and amorphous structure. The proportion of calcium in the collagen peptides chelated calcium gradually increased, confirming that more calcium was chelated by collagen peptides. The above results suggest that high-energy wet ball milling can be applied to produce fish collagen peptide chelated calcium, which has the advantages of simple processing, no pollution, and high chelation rate.