Production of β ‐glucan and related glucan‐hydrolases by Botryosphaeria rhodina

Aims:  Characterization of β ‐glucan production from Botryosphaeria rhodina DABAC‐P82 by detecting simultaneously glucan‐hydrolytic enzymes and their localization, culture medium rheology and oxygen transfer. Methods and Results:  Mycelium growth, β ‐glucan production, substrate consumption and glucan‐hydrolytic enzymes were monitored both in shaken flasks and in a 3‐l stirred‐tank bioreactor. Glucan production (19·7 and 15·2 g l −1 , in flask and bioreactor, respectively) was accompanied by extra‐cellular and cell‐bound β ‐glucanase and β ‐glucosidase activities. In the bioreactor scale, in the time interval of 0–78 h the apparent viscosity of the culture broth exhibited a general increase; thereafter, it began to reduce, probably because of the above glucan‐hydrolytic activities. Moreover, the culture media collected after 45 h behaved as solid‐like materials at shear rates smaller than 0·001 s −1 , as pseudo‐plastic liquids in the middle shear rate range and as Newtonian ones at shear rates greater than 1000 s −1 . Conclusion:  The greatest β ‐glucan accumulation in the bioreactor was found to be associated with nitrogen and dissolved oxygen concentrations smaller than 0·15 g l −1 and 25%, respectively, and with the peak points of the glucan‐degrading enzymes. Significance and Impact of the Study:  A careful analysis of the critical factors (such as, culture broth rheology, oxygen mass transfer and glucan‐hydrolytic enzymes) limiting the β ‐glucan production by B. rhodina is a prerequisite to maximize β ‐glucan yield and production, as well as to define the process flow sheet capable of maximizing biopolymer recovery, solvent re‐utilization and glucose consumption.