Agro-industrial by-products are a potential source of added-value phenolic acids with promising applications in the food and pharmaceutical industries. Here two purified feruloyl esterases from Aspergillus niger, FAEA and FAEB were tested for their ability to release phenolic acids such as caffeic acid, p-coumaric acid and ferulic acid from coffee pulp, apple marc and wheat straw. Their hydrolysis activity was evaluated and compared with their action on maize bran and sugar beet pulp. The specificity of both enzymes against natural and synthetic substrates was evaluated; particular attention was paid to quinic esters and lignin monomers. The efficiency of both enzymes on model substrates was studied. We show the ability of these enzymes to hydrolyze quinic esters and ester linkages between phenolic acids and lignin monomer.