  We evaluate the pseudoscalar-meson octet-baryon coupling constants and the
corresponding axial charges in eight channels ($\pi N\N$, $\pi\Sigma\Sigma$,
$\pi\Lambda\Sigma$, $K\Lambda N$, $K \Sigma N $, $\pi\Xi\Xi$, $K\Lambda\Xi$ and
$K\Sigma\Xi$) in lattice QCD with two flavors of dynamical quarks. The
parameter $\alpha\equiv F/(F+D)$ representing the SU(3)-flavor symmetry is
computed at each u,d-quark hopping parameter and at the flavor-SU(3) symmetric
point where the three quark flavors are degenerate at the physical $s$-quark
mass. In particular, we obtain $\alpha=0.395(6)$ at the SU(3) symmetric limit.
The quark-mass dependences of the coupling constants are obtained by changing
the $u$- and the $d$-quark masses and we find that the SU(3)-flavor symmetry is
broken by only a few percent at each quark-mass we employ.
