Hydrodynamic and kinetic study of cellulase production by Trichoderma reesei with pellet morphology.

Numerical simulations and experimental validation were performed to understand the effects of hydrodynamics on pellet formation and cellulase production by filamentous T. reesei. The constructed model combined a steady-state multiple reference frame (MRF) approach describing mechanical mixing, oxygen mass transfer, and non-Newtonian flow field with a transient sliding mesh approach and kinetics of oxygen consumption, pellet formation, and enzyme production. The model was experimentally validated at various agitation speeds in a two-impeller Rushton turbine fermentor. Results from simulation and experimentation showed that higher agitation speeds led to increases in the pellet diameter and the proportion of pelletized (vs. filamentous) forms of the biomass. It also led to increase in dissolved oxygen mass transfer rate in shear-thinning fluid and cellulase productivity. The extent of these increases varied considerably among agitation speeds. Pellet formation and morphology were presumably affected within a viscosity-dependent shear-rate range. Cellulase activity and cell viability were shown to be sensitive to impeller shear. A maximum cellulase activity of 3.5 IU/mL was obtained at 400 rpm, representing a twofold increase over that at 100 rpm.

Construction of an industrial brewing yeast strain to manufacture beer with low caloric content and improved flavor.

In this study, the problems of high caloric content, increased maturation time and off-flavors in commercial beer manufacture arising from residual sugar, diacetyl, and acetaldehyde levels were addressed. A recombinant industrial brewing yeast strain (TQ1) was generated from T1 [Lipomyces starkeyi dextranase gene (LSD1) introduced, alpha-acetohydroxyacid synthase gene (ILV2) disrupted] by introducing Saccharomyces cerevisiae glucoamylase (SGA1) and a strong promoter PGK1 while disrupting the genes coding alcohol dehydrogenase (ADH2). The highest glucoamylase activity for TQ1 was 93.26 U/ml compared with host strain T1 (12.36 U/ml) and wild-type industrial yeast strain YSF5 (10.39 U/ml), respectively. European Brewery Convention (EBC) tube fermentation tests comparing the fermentation broths of TQ1 with T1 and YSF5 showed that the real extract were reduced by 15.79% and 22.47%; the main residual maltotriose concentration were reduced by 13.75% and 18.82%; the caloric content were reduced by 27.18 and 35.39 calories per 12 oz. Due to the disruption of ADH2 gene in TQ1, the off-flavor acetaldehyde concentration in the fermentation broth were 9.43% and 13.28% respectively lower than that of T1 and YSF5. No heterologous DNA sequences or drug-resistance genes were introduced into TQ1. So, the gene manipulations in this work properly solved the addressed problems in commercial beer manufacture.