The dispensing assembly comprises a double cartridge having two storage containers with bags placed therein, a mixer that is connectable to the cartridge, and an opening means acting upon the bag. The opening means is arranged on the mixer housing and rotatable with respect to the cartridge and in one exemplary embodiment has a cutting member with two knife-edges that are arranged essentially parallelly to and spaced apart from the longitudinal axis and provided with cutting edges. Thanks to the rotatable knife-edges, such a cutting member allows a clean and predetermined opening of the bags and a dispensing operation with minimum pressure losses and lost volumes.