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Besides the identified key factors of pH-shift from 3.0 to 4.5 on day 4 and dissolved oxygen tension (DOT) shift from 25 to 10% on day 6, lower shear stress was also demonstrated to be a key factor in scaling-up the fed-batch fermentation of the medicinal mushroom Ganoderma lucidum from a shake flask to a stirred-tank bioreactor. The maximal biomass (22.62 g/L), intercellular polysaccharide production (4.74 g/L), and ganoderic acid production (798.0 mg/L) were attained at a low impeller tip speed of 1.234 m/s. Based on the identified key factors of pH-shift, DOT-shift and lower shear stress, the fed-batch fermentation of G. lucidum was successfully step-wise scaled-up from 7.5- to 200-L stirred-tank bioreactor. Through the qualitative and quantitative side-by-side comparison of G. lucidum growth and metabolites accumulation, it was concluded that the comparability of the fed-batch fermentation process were well controlled and the products were maintained during the process scale-up.

Truffles are hypogeous ascomycetes and ectomycorrhizal fungi with unique organoleptic properties. Effects of nitrogen source and its concentration were studied during the submerged fermentation of Chinese truffle Tuber sinense. Yeast extract was identified to be the most favorable for the cell growth, and the next was peptone. The maximal dry cell weight of 19.53 ± 0.13 g/L obtained at an initial yeast extract concentration of 25 g/L was higher by 40.9% compared to that at 10 g/L. Within the range of initial peptone concentration (i.e., 10, 20, 30 and 40 g/L) as investigated, the maximal biomass and the production of extracellular polysaccharide (EPS) were obtained at 30 g/L, while 20 g/L was favorable for the production of intracellular polysaccharide (IPS). A mathematical model, which was constructed by response surface methodology combination with Box-Behnken design (BBD), was applied to study the synergic effect of glucose, yeast extract and peptone. According to the model prediction, the optimal initial concentration of glucose, yeast extract and peptone was 60, 30 and 10 g/L, respectively. The validation experiment showed the experimental values agreed with the predicted values well. The highest biomass (i.e., 23.94 ± 0.49 g/L), the production of EPS (i.e., 1.59 ± 0.06 g/L) and IPS (i.e., 1.48 ± 0.26 g/L) were obtained under the predicted optimal conditions, which were higher by 22.6%, 42.0% and 16.5% compared with the best results of one-variable-at-a-time experiments, respectively.