Ferulic acid biotransformation has a number of interesting industrial uses. Ferulic acid biotransformation by the wild strain Aspergillus niger C28825 and a diploid strain DAR2, obtained by parasexual recombination, was studied. The wild strain of A. niger C28825 biotransforms ferulic acid to vanillic acid (VA): while the diploid strain DAR2 preferentially decarboxylates ferulic acid to 4-vinylguaiacol (4VG). The latter was identified by mass spectroscopy, (1)H and (13)C nuclear magnetic resonance spectroscopy, and quantified by HPLC. The diploid strain A. niger DAR2 and the wild strain showed a ferulic acid conversion of 64% and 36%, respectively. Molar yields show that the formation of 4VG was preferred, being as much as 4.4 times higher than the formation of VA in diploid strain cultures. Differential regulation of enzymes involved in the biotransformation of ferulic acid may explain the accumulation of 4VG by diploid DAR2. This strain produced both 4VG and VA. (C) 2010 Elsevier Ltd. All rights reserved.