Optimization of the medium composition for the submerged culture of Ganoderma lucidum by Taguchi array design and steepest ascent method

The operating conditions for a shake-flask culture of Ganoderma lucidum were studied. Of the carbon sources examined, brown sugar and malt extract most effectively promoted mycelial growth and the production of polysaccharide, while yeast extract and skim milk were the most effective nitrogen sources. Adding safflower seed oil to the medium significantly promoted the formation of mycelium. Additionally, supplying CaCO3 promoted both the mycelial growth and the polysaccharide production. The optimal initial pH and incubation temperature were 6.5 and 34 °C, respectively. The medium composition was then optimized using a systematic method that integrated the Taguchi array method and the steepest ascent method. The mycelium yield and the polysaccharide production were considered as two product quality variables. A desirability function was applied to combine these two qualities as a single objective function. The steepest ascent method was demonstrated effectively and efficiently to approach the neighborhood of the optimum. The optimum medium composition was found to be 1.88 g l−1 CaCO3, 71.4 g l−1 brown sugar, 12.1 g l−1 malt extract, 2.28 g l−1 yeast extract, 18.4 g l−1 skim milk, 3.44 g l−1 safflower seed oil, 3.96 g l−1 olive oil, pH 6.5. When the strain was cultivated in the obtained optimal medium under the optimal operating conditions, compared to the one before this study, the mycelium formation was markedly improved from 1.70 to 18.70 g l−1. Additionally, the polysaccharide production also increased markedly from 0.140 to 0.420 g l−1.