  We derive the next-to-leading order correction to the Nambu-Jona-Lasinio
model starting from quantum chromodynamics. So, we are able to fix the
constants of the Nambu-Jona-Lasinio model from quantum chromodynamics and
analyze the behavior of strong interactions at low energies. The technique is
to expand in powers of currents the generating functional. We apply it to a
simple Yukawa model with self-interaction showing how this has a
Nambu-Jona-Lasinio model and its higher order corrections as a low-energy
limit. The same is shown to happen for quantum chromodynamics in the chiral
limit with two quarks. We prove that a consistent thermodynamic behaviour is
obtained as expected for the given parameters.
