  By considering a flavour expansion about the SU(3)-flavour symmetric point,
we investigate how flavour-blindness constrains octet baryon matrix elements
after SU(3) is broken by the mass difference between the strange and light
quarks. We find the expansions to be highly constrained along a mass trajectory
where the singlet quark mass is held constant, which proves beneficial for
extrapolations of 2+1 flavour lattice data to the physical point. We
investigate these effects numerically via a lattice calculation of the
flavour-conserving and flavour-changing matrix elements of the vector and axial
operators between octet baryon states.
