Study and improvement of the processes and conditions for mycelial fermentation of a Cordyceps sinensis fungus.

摘要

Cordyceps sinensis (Berk.) Sacc., general called Cordyceps, is a precious medicinal fungus and has been used as an herbal remedy in China for hundreds of years. The natural scarcity of wild Cordyceps plus the increasing demand in recent years have motivated an enormous interest in fermentation production of Cordyceps fungal biomass and components. A new C. sinensis fungus was isolated from a wild Cordyceps fruiting body, designated as Cs-HKI, and was used to investigate Cs-HK1 mycelial liquid fermentation conditions and processes for efficient production of mycelial biomass and bioactive compounds.;Glucose and yeast extract were found to be the most favorable carbon and nitrogen sources, and 20--22 °C the most favorable temperature for the Cs-HK1 mycelial growth. Under these conditions the Cs-HK1 mycelial culture attained a maximum specific growth rate of 1.8 d-1, a maximum biomass density of 20--25 g dw/l in 6--7 days, a cordycepin content of 35--40 ∣microg/g dw in mycelial biomass, and an EPS yield of 2.5 g/l. The enhancement of cordycepin accumulation with ammonium feeding was attributed to the uptake of ammonia for nucleoside synthesis.;The mycelial culture process was successfully scaled up to pilot and industrial fermenters from 50 L to 10,000-L, achieving the similar mycelial biomass (20--25 g/l) and EPS yield (4--5 g/l) to those in the shake flasks. Exopolysaccharide (EPS) produced in the Cs-HK1 mycelial culture (isolated from culture medium by ethanol precipitation) contained 65--70% sugar and about 25% protein with a molecular weight (MW) ranging from 3.5 kDa to 250 kDa. Infrared spectrometry of EPS and gas chromatography of acetylated EPS suggested that the EPS had a beta-D-glucan backbone. The EPS had a Trolox equivalent antioxidant capacity of 35--40 micromol/g and a ferric reducing ability of plasma of 50--52 micromol Fe(II)/g, proving its antioxidant properties.;This project has accomplished a comprehensive study on the culture conditions and characteristics of Cs-HK1 fungus, the accumulation of bioactive compounds in the mycelia cultures, chemical properties and bioactivities of culture products. As demonstrated in the project, the Cs-HK1 mycelial culture can be applied for efficient production of bioactive Cordyceps components and polysaccharides with potential value for health food and medicine.