We extend a previous analysis concerning cosmological fluids with generalized
equations of state in order to study inflationary scenarios. In the framework
of the slow-roll approximation we find the expressions for the perturbation
parameters ϵ, η and the density perturbation spectra in terms of
the adiabatic index \ga as a function of the universe scale factor. This
connection allows to find straightforwardly \ga corresponding, for example,
to the simplest {\it chaotic} model and to the Harrison-Zeldovich potential and
shows its capability to be applied to more complicate situations. Finally, we
use this description to develop a new approach to the early universe dynamics,
based on a 1/N expansion, where N is the e-fold number. To this aim, we
introduce a set of suitable dimensionless variables and show that at the
zero-th order in 1/N, an improved slow-roll approximation is obtained.Comment: 15 pages, plain Latex, to appear in Mod. Phys. Lett.