It is shown that the large density fluctuations appearing at the onset of the first order nuclear liquid-gas phase transition can play an important role in thesupernovae evolution. Due to these fluctuations, the neutrino gas may betrapped inside a thin layer of matter near the proto-neutron star surface. The resulting increase of pressure may induce strong particle ejection a few hundred milliseconds after the bounce of the collapse, contributing to the revival of the shock wave. The Hartree-Fock+RPA scheme, with a finite-range nucleon-nucleon effective interaction, is employed to estimate the effects of the neutrino trapping due to the strong density fluctuations, and to discuss qualitatively the consequences of the suggested new scenario.