  A recent paper by Kumar (2012) (hereafter K12) claimed that in a contracting
model, described by perturbations around a collapsing Friedmann model
containing dust or radiation, the perturbations can grow in such a way that the
linearity conditions would become invalid. This conclusion is not correct due
to the following facts: first, it is claimed that the linearity conditions are
not satisfied, but nowhere in K12 the amplitudes of the perturbations were in
fact estimated. Therefore, without such estimates, the only possible conclusion
from this work is the well known fact that the perturbations indeed grow during
contraction, which, per se, does not imply that the linearity conditions become
invalid. Second, some evaluations of the linearity conditions are incorrect
because third other terms, instead of the appropriate second order ones, are
mistakenly compared with first order terms, yielding artificially fast growing
conditions. Finally, it is claimed that the results of K12 are in sharp
contrast with the results of the paper by Vitenti and Pinto-Neto (2012)
(hereafter VPN12), because the former was obtained in a gauge invariant way.
However, the author of K12 did not realized that the evolution of the
perturbations were also calculated in a gauge invariant way in VPN12, but some
of the linearity conditions which are necessary to be checked cannot be
expressed in terms of gauge invariant quantities. In the present work, the
incorrect or incomplete statements of K12 are clarified and completed, and it
is shown that all other correct results of K12 were already present in VPN12,
whose conclusions remain untouched, namely, that cosmological perturbations of
quantum mechanical origin in a bouncing model can remain in the linear regime
all along the contracting phase and at the bounce itself for a wide interval of
energy scales of the bounce. (Abstract abridged)
