Enzyme and Microbial Technology 40 (2007) 801–805 Production of xylanase by Trichoderma longibrachiatum on a mixture of wheat bran and wheat straw: Optimization of culture condition by Taguchi method Mehrdad Azin ∗ , Roya Moravej, Davood Zareh Biotechnology Research Center, Iranian Research Organization for Science & Technology, P.O. Box 15815-3538, Tehran, Iran Received 14 June 2006; accepted 14 June 2006 Abstract The usefulness of Taguchi method for optimization of culture condition, designed for production of xylanase by Trichoderma longibrachiatum was investigated. L16 orthogonal array, by which the effect of five factors in four levels, could be tested, was chosen. Analysis of variance (ANOVA) was performed on the obtained results and optimum condition suggested by statistical calculations was tested in a verification test. An increase of 41.9% in xylanase production was observed, after performing optimization techniques, including one-factor-at-a-time (OFAT) and Taguchi method, which indicates suitability of this method in microbiological processes optimizations. © 2006 Elsevier Inc. All rights reserved. Keywords: Optimization; Orthogonal array; Taguchi method; Trichoderma longibrachiatum; Xylanase 1. Introduction Microbial enzymes like xylanases are important additives in numerous areas from food processing to paper and pulp industries. These enzymes improve nutrient digestibility in cer- tain diets both in ruminants and poultries, where no digesting enzymes which can digest complex cell wall carbohydrates, exist. The positive performance of these enzymes is demon- strated clearly in nutrition of poultries [1–3], biobleaching of paper pulp [4] and improving the baked products [5,6]. Xylanase hydrolyzes xylosidic linkages in xylan polymers [7–12]. Solid-state fermentation (SSF), whereby an insoluble sub- strate is fermented with sufficient but no free moisture [13], typically uses agricultural residues such as wheat bran, wheat straw, rice bran, etc. for production of larger amounts of micro- bial metabolites at a lower cost [14–17], although, normally the production of industrial enzymes, like xylanase is performed by submerged culture [18,19]. Optimal environmental condition is a prerequisite for promotion of maximum growth and production of enzymes where SSF is used [20,21]. ∗ Corresponding author. Tel.: +98 21 88838350; fax: +98 21 88838350. E-mail address: azin@irost.org (M. Azin). Trichoderma spp., major agents of agricultural waste decom- position and decay, possess a broad range of enzymes, and hence are known as good producers of lignocellulolytic enzymes [17,19,22]. However, use of other microorganisms from king- dom of bacteria such as Bacillus sp. [21], Cellulomonas [23], Streptomyces sp. [24], Thermomonospora [25], Thermotoga [11], and other thermophiles [26] and many species from fungi like white- or brown-rot fungi [27] and even anaerobic fungi [28] is documented. Optimization of production of xylanase is a prerequisite for it’s economical manufacturing. In this regard, normally the response surface method (RSM) is preferred by biolo- gists [29]. Even for enhancement of xylanase production, this method has been used [30,31]. Taguchi method, as another way for designing fractional factorial experiments [32], is some- how not very well known for optimization of biotechnological processes. In this article, the effect of different proportions of substrates, growth temperature, initial pH, moisture level, inoculum’s size, and nitrogen source, each in four levels, were optimized by Taguchi method. The results of experiments performed for obtaining optimum levels of xylanase by Trichoderma longi- brachiatum, using easily available substrates, like wheat straw and wheat bran in SSF, are discussed. 0141-0229/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2006.06.013