Introduction

Feruloyl esterases (ferulic acid esterase, cinnamoyl esterase, cinnamoyl ester hydrolase, FAE,* FE, etc.) belong to the class of carboxylesterases (EC 3.1.1.1). These esterases catalyze the hydrolysis of ester-linked ferulic acid groups from a wide range of substrates. The product is a phenolic carboxylic acid and an alcohol.

* Abbreviations: AEBSF, 4-(2-amino-ethyl)-benzenesulfonyl fluoride; AraF, ferulic acid-arabinose ester; BLAST, basic local alignment search tool; CinnAE, type-B feruloyl esterase from Aspergillus niger; DFP, di-isofluorophosphate; EDTA, ethylenediaminetetra-acetic acid; FAE, feruloyl esterase; FAEA, type-A feruloyl esterase from Aspergillus niger; FE, feruloyl esterase; HPLC, high-pressure liquid chromatogra-phy; MFA, methyl ferulate; SDS-PAGE, sodium dodecylsul-fate polyacrylamide gel electrophoresis.

* Abbreviations: AEBSF, 4-(2-amino-ethyl)-benzenesulfonyl fluoride; AraF, ferulic acid-arabinose ester; BLAST, basic local alignment search tool; CinnAE, type-B feruloyl esterase from Aspergillus niger; DFP, di-isofluorophosphate; EDTA, ethylenediaminetetra-acetic acid; FAE, feruloyl esterase; FAEA, type-A feruloyl esterase from Aspergillus niger; FE, feruloyl esterase; HPLC, high-pressure liquid chromatogra-phy; MFA, methyl ferulate; SDS-PAGE, sodium dodecylsul-fate polyacrylamide gel electrophoresis.

Arabinoxylans and certain pectins contain ester-linked ferulic acid as shown in Figures 1 and 2 (1). The ferulic acid can be either monomeric or in one of several dimeric forms (2) (Fig. 3). Free ferulic acid and two of the ferulate dimers (5-5' mainly, but also the 8-0-4'-linked dimer) are released from arabinoxylans in wheat bran or from pectins in sugar beet pulp by some fer-uloyl esterases. This activity is greatly enhanced by xylanases (3).

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