Specificity of ferulic acid (feruloyl) esterases G. Williamson’, C. B. Faulds and P. A. Kroon Biochemistry Department, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. 205 moyl esters (manifest as a K,,, of between lop6 Feruloyl esterases are a subclass of the carboxylic ester hydrolases (EC 3.1.1.1) which hydrolyse ester linkages between hydroxycinnamates and sugars. These types of ester linkage are found in a wide variety of plant cell walls [ 11. The feruloyl esterase activities reported to date are predominantly microbial (Table l ) , and these types of enzymes are secreted by several species to facilitate breakdown of the plant cell wall as a food source. Although there are many types of esterase, the unique feature of the feruloyl esterases is their specificity for hydrolysis of hydroxycinna-