Separation of lysozyme from salted duck egg white by affinity precipitation using pH-responsive polymer with an l-thyroxin ligand

•Lysozyme has been purified from salted duck egg white by affinity precipitation.•The pH-responsive polymer PMMDN immobilized l-thyroxin as affinity ligand.•Scanning electron microscope showed the surface morphologies of the polymers during affinity precipitation.•The maximum elution recoveries were 94.32% (protein) and 96.79% (activity).•SDS–PAGE showed the electrophoretically pure lysozyme could be obtained.

Lysozyme could be efficiently purified using affinity precipitation by using a pH-responsive polymer PMMDN with l-thyroxin as affinity ligand. A pH-responsive polymer PMMDN was polymerized and subsequently coupled with l-thyroxin as the ligand. The pI of the affinity polymer was 4.65 and the recovery was 96.7% of its original amount after recycling three times. The Optimal adsorption condition was 0.02 M phosphate buffer (pH 5.5) with 1.0 mol/L NaCl, and the adsorption isotherm showed the maximum adsorption capacity as 22.76 mg/g polymer, the dissociation constant as 0.085 mg/ml, and the label-free detection data analyzed by ForteBio’s Octet also verified the results. The recovery of total lysozyme by elution with 0.2 mol/L Gly-NaOH buffer (pH 10.0), and the maximum elution recoveries were 94.32% (protein) and 96.79% (activity). The surface morphologies of the samples in the whole process of affinity precipitation were obtained by scanning electron microscope (SEM).

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