Stainless Steel :
stainless steel nozzles are prefer when printing items intended for food service or human body contact, since typical nozzle brass alloys contain trace amounts of lead. It's not clear whether this is a realistic concern or not. The lead would have to first leach from the brass into the molten plastic, and then leach from the finished item into food. There hasn't been any rigorous research into the quantities of lead that may end up in food.
Specification of Brass Nozzle: