Optimization of submerged-culture conditions for mycelial growth and exo-biopolymer production by Auricularia polytricha (wood ears fungus) using the methods of uniform design and regression analysis
This paper is concerned with the optimization of submerged culture conditions for mycelial growth and exo-biopolymer production by Auricularia polytricha by one-factor-at-a-time and uniform design (UD) methods. First, the one-factor-at-a-time method was adopted to investigate the effects of environmental factors (i.e., initial pH and temperature) and variables of medium components (i.e., carbon, nitrogen and mineral sources) on mycelial growth and exo-biopolymer production. Sucrose, yeast extract, and K2HPO4 were identified to be the most suitable carbon, nitrogen, and mineral sources, respectively. The optimal temperature and initial pH for mycelial growth and exo-biopolymer production were found to be 25 degrees C and 5.0, respectively. Subsequently, the concentrations of sucrose, yeast extract, and K2HPO4 were optimized using the UD method. The optimal concentrations for the enhanced production were determined as 6% (w/v) sucrose, 2.5% (w/v) yeast extract, and 0.3% (w/v) K2HPO4 for mycelial yield, and 6% (w/v) sucrose, 1.28% (w/v) yeast extract, and 0.3% (w/v) K2HPO4 for exo-biopolymer production, respectively. Subsequent experiments confirmed the validity of the models. This optimization strategy in shake-flask culture led to a mycelial yield of 6.14 g/l, and exo-biopolymer production of 2.12 g/l, respectively, which were considerably higher than those obtained in the preliminary studies. By using the optimized medium, the maximum concentrations of mycelial biomass and exo-biopolymer in a 5 litre stirred-tank bioreactor indicated 35.3 g/l and 3.1 g/l, respectively.