Laccase production by Pleurotusostreatus 1804: Optimization of submerged culture conditions by Taguchi DOE methodology

Submerged culture conditions for laccase production by Pleurotus ostreatus 1804 were optimized by Taguchi orthogonal array (OA) experimental design (DOE) methodology. This approach facilitates the study of interaction of a large number of variables spanned by factors and their settings with a small number of experiments leading to considerable saving in time and cost for the process optimization. The proposed Taguchi DOE methodology consists of four phases viz., planning, conducting, analysis and validation, which were connected sequence wise to achieve the overall process optimization. Eight factors viz., carbon, nitrogen source (urea), 2,5-xylidine (inducer), wheat bran (ligninocellulosic material), inoculum size, fermentation broth pH, yeast extract and phosphate source (KH2PO4) at three levels with a OA layout of L18 (21 × 37) were selected for the proposed experimental design. Laccase yield obtained from the 18 sets of fermentation experiments performed with the selected factors and levels were further processed with Qualitek-4 software at bigger is better as quality character. The optimized conditions showed an enhanced laccase expression of 32.9% (from 538.8 to 803.3 U). The optimal combinations of factors obtained from the proposed DOE methodology was further validated by conducting fermentation experiments and the obtained results revealed an enhanced laccase yield of 28.3%. Taguchi approach of DOE resulted in evaluating the main and interaction effects of the factors individually and in combination. This methodology facilitated analysis of the experimental data to establish the optimum conditions for the process, understand the contribution of individual factors and to evaluate the response under optimal conditions. Application of Taguchi approach appears to have potential usage in bioprocess optimization.