A major bioactive component of plant cell walls, ferulic acid, influences feruloyl esterase production in Aspergillus niger.

Abstract

Ferulic acid is a major bioactive component of wheat bran (0.5-196, w/w dry matter) [l], maize bran (3%) [2], barley (0.02%) and spent grain (0.17%) [3]. Ferulic acid has antioxidant properties [4], and is involved in the nitrite scavenging effect of wheat bran [5]. The phenolic acid is esterlinked to arabinose or galactose in plant cell wall polysaccharides, and microbial esterases hydrolyse this bond to release the free acid from cell wall preparations [6]. These type of esterases have also been detected in human gut microflora 171. The feruloyl esterases from Aspergillus niger are known to be induced by the carbon source [9,10], but the nature of the inducing compound(s) is not known. In this paper, we examine different cell wall preparations, containing different ferulic acid concentrations, for their ability to induce the esterases. A . niger, a filamentous fungi, was grown over a 10-day period on either oat spelt xylan, de-starched wheat bran or destarched maize bran (all 1 % w / ~ , supplemented with 0.1 % w/v glucose) at 25C, under agitation at 120 rpm. Aliquots were removed daily and analyzed for esterase activity by a spectrophotometric assay [8], using methyl esters (33 pM) of ferulic (MFA), sinapic (MSA), caffeic (MCA) or coumaric acid (MpCA). Activity is expressed as pmol acid released/min at