gamma-decalactone production by Trichoderma harzianum in stirred bioreactors

Production of gamma-decalactone, a compound having peach-lice aroma characteristics, by a strain of Trichoderma harzianum is reported here for the first time. Cultures were carried out in a 14 L fermenter using castor oil as the sole carbon source. The, filamentous-like growth of the microorganism resulted in highly viscous and non-Newtonian broths, which caused the formation of stagnant zones in the fermenter. T. harzianum was able to produce 260 mg/L of gamma-decalactone after 7 days of culture in a stirred fermenter operated at 3.3 s(-1) and 1: vvm of air now rate. The production of gamma-decalactone was mainly non-growth associated. The use of high agitation,rates-to improve mixing-resulted in celullar lysis. Cell damage occurred at volumetric power drawn as low as 0.2 W/L. Mycelial morphology (mainly hyphal thickness) changed drastically along the culture and was an important influence on the rheology of the broths. All these characteristics make this system an interesting model of study of hydrodynamically complex fermentations involving up to four phases.