  Non-perturbative QCD vacuum effects at finite density are parametrized by
means of a bag constant $B$. It is extracted from a Nambu- Jona Lasinio model
with two or three flavors. The parameter $B$ is used in an effective
quark-meson coupling model to study the nuclear phenomenology. We examine the
nucleon structure and the thermodynamical properties of symmetric nuclear
matter, particular attention is paid to the symmetry energy and to the eventual
phase transition to deconfined quark matter. An alternative sketch of the
binding mechanism of symmetric nuclear matter emerges within this approach. It
is also found that the inclusion of strangeness content in $B$ is crucial for
an appropriate description.
