Abstract: The aim of this study was to provide an efficient method for the separation of organic acids from apple juice. Magnetic Fe3O4/chitosan microspheres were prepared by inverse suspension cross-linking method and were characterized by a scanning electron microscope, a laser particle size analyzer, a Fourier transform infrared spectrometer, a thermal gravimetric analyzer, an X-ray diffractometer, and a superconducting quantum magnetic measurement system. Also, the recovery rates of the magnetic Fe3O4/chitosan composite microspheres and pure Fe3O4 microspheres were determined as a function of time (0-5 min) and pH (pH 2-11) under a certain magnetic field intensity. Then, the composite microspheres were used to adsorb and desorb organic acids from apple juice for three times. The composite microspheres owned a narrow size distribution ranging from 22 to 158 μm, had good dispersity and were regularly spherical in shape. The X-ray diffraction (XRD) patterns indicated that chitosan coating procedure did not change the spinal structure of magnetic Fe3O4 nanoparticles. Fourier transform infrared and thermogravimetric analyses demonstrated that chitosan was coated on Fe3O4 nanoparticles successfully and Fe3O4 was accounted for about 38.66% of the composite microspheres. The saturated magnetization of the composite microspheres was 35.98 emu/g. The microspheres showed a high recoverability of 99.99% in 2 minutes, obviously higher than that of pure Fe3O4 nanoparticles. After three cycles of adsorption and desorption, the equilibrium adsorption capacity was still as high as 109.92 mg/g and the recovery rate of organic acids was 86.86%. These results showed that the magnetic Fe3O4/chitosan composite microspheres had good magnetic response and good recoverability and could be repeatedly used to efficiently separate organic acid from apple juice as an environmental friendly adsorbent.

Key words: magnetic Fe3O4/chitosan composite microspheres, adsorption, apple juice, organic acids