Abstract
Edible filamentous fungi L. edodes (shiitake mushrooms) were cultivated in submerged fermentation in stirred tank bioreactors (STR) both in batch and semicontinuous cultivation in a corn steep liquor (CSL) medium. The adjustment of a combination of constant impeller agitation speed, a short duration of a high-speed agitation (burst), and the frequency of bursts improved biomass (cell dry weight (CDW) titre from 1.75 to 4.95 g/L in a 96-h batch cultivation. These bioreactor process conditions were applied to a semicontinuous culture strategy to produce similar biomass density at a dilution rate of 0.02 h(-1) for up to 10 days without washout over the duration of the fermentation. An increase in the dilution rate above 0.02 h(-1) resulted in washout of L. edodes over time. Using a richer growth medium through the addition of malt extract, peptone, and molasses allowed L. edodes to grow to 4.7 g/L at a dilution rate of 0.025 h(-1) without washout. The maximum biomass productivity (396 mg CDW/h) of the semicontinuous cultivation (D = 0.02 h(-1)) was 1.9-fold higher than the batch cultivation 206 mg CDW/hour. Use of the richer growth medium at D = 0.025 h(-1) improved biomass productivity further to 470 mg/h. Glucans, known bioactives, were present in the fungal biomass at a maximum of 14% of the cell dry weight (CDW) with b-glucans predominating over a-glucans. KEY POINTS: • Short, high-speed impeller bursts homogenise mycelia preventing bioreactor clogging. • Semicontinuous fermentation at D of 0.02 h-1 generated 5.1 g/L of fungal biomass. • Cultivation of fungal biomass in STR resulted in biomass with 14% of total glucans.