You would separate antioxidants by looking at the properties of the antioxidant and then doing a procedure called an extraction. This would require that the fruit was partially digested (easily by blending the fruit into a soupy mixture), then using non-polar solvents an extraction with this solvent, followed by separation chromatography as needed. This would remove the small molecule that acts as the antioxidant. I can't find any easy procedures to do at home, therefore this must be done in a laboratory.