A mixture of wheat bran with maize bran as a carbon source and addition of (NH4)SO4 as nitrogen source was found to significantly increase production of feruloyl esterase (FAE) enzyme compared with wheat bran as a sole carbon and nitrogen source. The optimal conditions in conical flasks were carbon source (30？g) to water 1？:？1, maize bran to wheat bran 1？:？2, (NH4)SO4 1.2？g and MgSO4 70？mg. Under these conditions, FAE activity was 7.68？mU/g. The FAE activity on the mixed carbon sources showed, high activity against the plant cell walls contained in the cultures. 1. Introduction Feruloyl esterases (FAEs; E.C. 3.1.1.73) are the enzymes responsible for cleaving the ester link between polysaccharides and monomeric or dimeric ferulic acid. This enzyme activity liberates phenolic acids (ferulic acid (FA) and p-coumaric acid) and their dimers from naturally occurring hemicelluloses and pectins [1, 2]. FAE has applications in the food, feed, and pharmaceutical industries, as well as in fuel production. Firstly, this enzyme can release ferulic acid from agrobyproducts, which can be used as antioxidants [1, 3] and transformed into other valuable molecules such as styrenes, polymers, epoxides, alkylbenzenes, vanillic acid derivatives, protocatechuric acid-related catechols, guaiacol, catechol, and vanillin [4]; secondly, FAE digestion can allow recovery of a number of phenolic compounds from nonwood fibers, such as wheat straw, rice straw, and sugarcane baggasse, while freeing up the resulting cellulose fibers for use in papermaking [5]; thirdly, the enzyme has synergistic effects on cellulase and xylanase activities for release of glucose and xylose from cellulose and hemicellulose for ethanol production [1, 6]; fourthly, FAE acts as a biosynthetic tool for formation of more lipophilic antioxidant derivatives [1]; fifthly, FAE has been used to improve the in vitro bioaccessibility and colonic metabolism of phenolic compounds in humans and to increase digestion of complex plant cell walls in animals [1, 7]. Many microorganisms have been reported to produce FAE. Among these, Aspergillus species, such as Aspergillus flavipes, Aspergillus awamori, Aspergillus niger, and Aspergillus oryzae, are the most active producers of feruloyl esterases [8–11]. In this research, A. niger was used to investigate the production of feruloyl esterases by solid fermentation on different substrates. 2. Materials and Methods 2.1. Materials Wheat bran was purchased from Nanfang Flour Co. Ltd., (Guangzhou, China), maize bran was obtained from Huabei Pharmaceutical Company (Hebei, China),
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