Abstract: The significance of developing amino acid-chelated copper is evident to reduce environmental pollution and nutrient wastes caused by the use copper inorganic salts in food and feed processing. In this experiment, L-hydroxyproline (L-Hyp) was prepared and separated from food grade pig skin gelatin and further used to obtain L-hydroxyproline-Cu(Ⅱ) (L-Hyp-Cu(Ⅱ) with CuSO4·5H2O by sequential microwave irradiation and solid-state synthesis under pressurized conditions. The synthesis conditions were established as follows: after thorough mixing of L-Hyp with CuSO4·5H2O at a molar ratio of 2.5:1 namely 10.5:8.0 (m/m), the reaction was triggered by adding 20 mL of water followed by addition of 5.6 g of anhydrous Na2CO3 for acid removal under microwave irradiation for 180 s at 600 W, and then transferred to a pressurized reaction kettle at 90 ℃ and 15 MPa with an agitation speed of 100 r/min for 35 min. The composition and structure of the final product were characterized by ultraviolet (UV) spectroscopy, infrared spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), coordination analysis, elemental analysis and gravimetry. Results indicated that this synthesis procedure gave higher chelate rate of L-Hyp-Cu(Ⅱ), reaching 86.4%. The chelating reaction between copper (Ⅱ) and carboxyl and imino groups in L-Hyp to fomr L-Hyp-Cu(Ⅱ) with a coordination ratio of 1:2, whose molecular formula was established as Cu(C5H8NO3)2.

Key words: L-hydroxyproline-Cu(Ⅱ), microwave-assisted solid-state method, pressurization, two-stage treatment, characterization