  Using general baryon interpolating fields $J_B$ for $B= N, \Xi, \Sigma, $
without derivative, we study QCD sum rules for meson-baryon couplings and their
dependence on Dirac structures for the two-point correlation function with a
meson $i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket$.
Three distinct Dirac structures are compared: $i\gamma_5$,
$i\gamma_5\fslash{p}$, and $\gamma_5\sigma_{\mu\nu}q^\mu p^\nu$ structures.
  From the dependence of the OPE on general baryon interpolating fields, we
propose criteria for choosing an appropriate Dirac structure for the coupling
sum rules. The $\gamma_5\sigma_{\mu\nu}q^\mu p^\nu$ sum rules satisfy the
criteria while the $i\gamma_5$ sum rules beyond the chiral limit do not. For
the $i\gamma_5\fslash{p}$ sum rules, the large continuum contributions prohibit
reliable prediction for the couplings. Thus, the $\gamma_5\sigma_{\mu\nu}q^\mu
p^\nu$ structure seems pertinent for realistic predictions. In the SU(3) limit,
we identify the OPE terms responsible for the $F/D$ ratio. We then study the
dependence of the ratio on the baryon interpolating fields. We conclude the
ratio $F/D \sim 0.6-0.8$ for appropriate choice of the interpolating fields.
