We continue the exploration of the BaLROG ( Bars in Low Redshift Optical Galaxies ) sample : 16 large mosaics of barred galaxies observed with the integral field unit SAURON .
We quantify the influence of bars on the composition of the stellar component .
We derive line-strength indices of H \beta , Fe5015 and Mg b .
Based on single stellar population ( SSP ) models , we calculate ages , metallicities and [ Mg/Fe ] abundances and their gradients along the bar major and minor axes .
The high spatial resolution of our data allows us to identify breaks among index and SSP profiles , commonly at 0.13 \pm 0.06 bar length , consistent with kinematic features .
Inner gradients are about ten times steeper than outer gradients and become larger when there is a central rotating component , implying that the gradients are not independent of dynamics and orbits .
Central ages appear to be younger for stronger bars .
Yet , the bar regions are usually old .
We find a flattening of the iron ( Fe5015 ) and magnesium ( Mg b ) outer gradients along the bar major axis , translating into a flattening of the metallicity gradient .
This gradient is found to be 0.03 \pm 0.07 dex/kpc along the bar major axis while the mean value of the bar minor axis compares well with that of an unbarred control sample and is significantly steeper , namely - 0.20 \pm 0.04 dex/kpc .
These results confirm recent simulations and discern the important localized influence of bars .
The elevated [ Mg/Fe ] abundances of bars and bulges compared to the lower values of discs suggest an early formation , in particular for early type galaxies .