Yes, even though this may sound odd since serum is generally known to inactivte proteases. We recommend it in this case, however, because the incubation times are quite long and the cells are stressed by the procedure. The amounts of enzymes should be high enough to have good residual activity, i.e. to achieve sufficient digestion. If you are concerned about the presence of serum, then you could reduce the concentration to 5% FCS. To get good digestion it is also important to cut the cartilage in thin slices and mince them with a scalpel.