In this work, we developed processes using ionic liquids to obtain size-defined soluble aromatic-rich streams from sorghum biomass to assess their biocompatibility with P. putida. Growth was unexpectedly higher than that observed on a main aromatic compound. Subsequently, proteomics and metabolomics analysis revealed that BCD liquor contains additional carbon sources except aromatics. Our comparative proteomic analysis first revealed significant up-regulation of a diverse set of proteins in P. putida grown in the complex lignolysate to understand their function and regulation.