The effective g-factor of 2D holes in modulation doped mbox{p-SiGe/Ge/SiGe} structures was studied. The AC conductivity of samples with hole densities from $3.9 times 10^{11}$~to $6.2 times 10^{11}~text{cm}^{-2}$ was measured in perpendicular magnetic fields up to $8~text{T}$ using a contactless acoustic method. From the analysis of the temperature dependence of conductivity oscillations, the $mathrm{g}_{perp}$-factor of each sample was determined. The $mathrm{g}_{perp}$-factor was found to be decreasing approximately linearly with hole density. This effect is attributed to non-parabolicity of the valence band.
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