Parasitic capacitance is generated by a linear current flow in adjacent windings of any inductor .To reduce this , increase the airgap between the winding coils .The diode (pn jn.)is a capacitance and stores charge in the poles P and N..
When both are coupled in kirchoffs mode ,they annul .However , you need to carefully choose the switching diode for the correct value of static parasitic value .
Ref. 1N4149 has static cap of 2pf.///1N5408 has 3.5pf and 1N4007 has excess of 7pf...These caps provide for propagation delay ,storage ,transient responses.