Highly Efficient Extraction of Ferulic Acid from Cereal Brans by a New Type A Feruloyl Esterase from Eupenicillium parvum in Combination with Dilute Phosphoric Acid Pretreatment.

Feruloyl esterase (FAE) is a critical enzyme in bio-extraction of ferulic acid (FA) from plant cell wall. A new FAE (EpFAE1) encoding gene was isolated from Eupenicillium parvum and heterologously expressed in Pichia pastoris cells. Based on phylogenetic tree analysis, the protein EpFAE1 belongs to type A of the seventh FAE subfamily. Using methyl ferulate as substrate, the optimum temperature and pH for the catalytic activity of EpFAE1 were 50 °C and 5.5, respectively. The enzyme exhibited high stability at 50 °C, in a wide pH range (3.0-11.0), or in the presence of 2 M of NaCl. Together with the endo-xylanase EpXYN1, EpFAE1 released 72.32% and 4.00% of the alkali-extractable FA from de-starched wheat bran (DSWB) or de-starched corn bran (DSCB), respectively. Meanwhile, the substrates were pretreated with 1.75% (for DSWB) or 1.0% (for DSCB) of phosphoric acid (PA) at 90 °C for 12 h, followed by enzymatic hydrolysis of the soluble and insoluble fractions. The release efficiencies of FA were up to 84.64% for DSWB and 66.73% for DSCB. Combined dilute PA pretreatment with enzymatic hydrolysis is a low-cost and highly efficient method for the extraction of FA from cereal brans.