A sterilization system for use in association with a filler device configured for filling at least one of rigid and flexible containers comprising a sterilization chamber and a sterilant supply assembly. The sterilization chamber includes a housing, an inlet into the housing, an outlet from the housing and a product retainer assembly. These components define a cavity within which to position a portion of a fitment. The sterilant supply assembly comprises a steam generating system having a steam supply conduit extending therefrom and a joint mixing conduit coupled with the inlet into the housing of the sterilization chamber, a hydrogen peroxide storing system and a member for metering liquid phase hydrogen peroxide from the hydrogen peroxide storing system into the steam supply conduit for mixing therewith, and, in turn, introduction thereof into the cavity of the sterilization chamber.