Identification and Characterization of Feruloyl Esterases Produced by Probiotic Bacteria

Abstract

A variety of phenolic compounds are naturally available, and contain one or more phenolic rings with or without substituents such as hydroxyl or methoxy groups. The term phytophenol, or phytochemical, is also used due to the widespread distribution of these chemicals throughout the plant kingdom (Huang et al., 2007). Phytophenols are secondary metabolites of plants, which are primarily used in defense against ultraviolet radiation and pathogens (Beckman, 2000). These chemicals also participate in the formation of macromolecular structures in plant cell walls, and are naturally present in the form of monophenols or polyphenols with ester linkages. The presence of phenolic ester linkages limits the hydrolytic activity of enzymes such as xylanases, cellulases, and pectinases, by shielding the site of hydrolysis on plant cell walls from these enzymes. Hydrolyzing the ester linkages within the phytophenols releases the phenolic acids and relaxes the structure of the plant cell wall, aiding in the degradation and maximizing the nutritional value of dietary fiber. Phenolic acids such as ferulic acid, caffeic acid, chlorogenic acid, and rosmarinic acid are studied extensively due to their anti-oxidative, anti-inflammatory, and other health related properties which have been demonstrated both in vitro and in vivo (Srinivasan et al., 2007). Even though phenolic acids can be easily found in dietary fiber, the ester linkages prevent their absorption in the human intestine. It has been demonstrated that only small monophenolic acids, but not esterified phenolic acids, can be absorbed efficiently by the monocarboxylic acid transporter (Konishi et al., 2005). Thus, an enzymatic step is required to convert the esterified phenolic acids into monophenolic acids prior to absorption. In the presence of water, a specific type of enzyme, feruloyl esterases (FAEs), is able to hydrolyze the phenolic compounds into respective alcohols and phenolic acids. Thus, FAEs become one of the target fields of study to improve the bioavailiability and assimilation of phenolic acids in the human diet.