  The many-fermion Lagrangian which includes the 't Hooft six-quark flavor
mixing interaction (N_f=3) and the U_L(3)\times U_R(3) chiral symmetric
four-quark Nambu -- Jona-Lasinio (NJL) type interactions is bosonized by the
path integral method. The method of the steepest descents is used to derive the
effective quark-mesonic Lagrangian with linearized many-fermion vertices. We
obtain, additionally to the known lowest order stationary phase result of
Reinhardt and Alkofer, the next to leading order (NLO) contribution arising
from quantum fluctuations of auxiliary bosonic fields around their stationary
phase trajectories (the Gaussian integral contribution). Using the gap equation
we construct the effective potential, from which the structure of the vacuum
can be settled. For some set of parameters the effective potential has several
extrema, that in the case of SU(2)_I\times U(1)_Y flavor symmetry can be
understood on topological grounds. With increasing strength of the fluctuations
the spontaneously broken phase gets unstable and the trivial vacuum is
restored. The effective potential reveals furthermore the existence of
logarithmic singularities at certain field expectation values, signalizing
caustic regions.
