The objective of this research was to improve Glucose-6-phosphate dehydrogenase (G6PD) production by Saccharomyces cerevisiae W303-181, which carry the plasmid YEpPGK-G6PD, by varying the following cultivation conditions: pH value (4.8, 5.7 and 6.6); inoculum concentration (0.1, 0.6 and 1.1 g/L) and initial glucose concentration (20.0, 30.0 and 40.0 g/L). The effect of those variables on G6PD production capability was studied by the application of response surface statistical analysis. The results showed that the highest G6PD production (1594.2 U/L), specific activity (1189.7 U/g cell) and productivity (45.6 U/L.h) occurred at pH 4.8, inoculum concentration of 0.1 g/L and initial glucose concentration of 20.0 g/L, under agitation of 150 rpm at 30ºC after 36 h. In this work, the strain expressed about 21 fold more activity than the wild S. cerevisiae strain, being an attractive and promising new source of this enzyme.

This paper analyzes the influence of pH, temperature and degree of hydrolyzate concentration on the removal of volatile and nonvolatile compounds from sugarcane bagasse hemicellulosic hydrolyzate treated with activated charcoal before or after the vacuum evaporation process. Furfural and 5-Hydroxymethylfurfural were almost totally removed in all the experiments, irrespective of pH and temperature and whether the charcoal was added before or after the vacuum evaporation process. Adding activated charcoal before the vacuum evaporation process favored the removal of phenolic compounds for all values of pH. Acetic acid, on the contrary, was most effectively removed when the activated charcoal was added after the vacuum evaporation process at an acid pH (0.92) and at the highest degree of hydrolyzate concentration (f=4). However, addition of activated charcoal before or after vacuum evaporation at an acid pH (0.92) and at the highest degree of hydrolyzate concentration (f=4) favored the removal of both acetic acid and phenolic compounds.

K. marxianus DSM 70106 was cultivated for inulinase production in a medium containing 2.0 g/L of yeast extract, 5.0 g/L of peptone and salts. The addition of corn steep liquor did not increase enzyme production. Inulin, as the main carbon source, afforded higher inulinase production than glucose, fructose, sucrose, lactose, maltose and starch. Glucose, fructose and sucrose reduced enzyme production by 46, 58 and 71%, respectively. By using the best culture medium enzyme activity remained stable for 22 months at 4oC; while at -18oC it decreased by 10%. Maximal activity was found in the pH range of 3.5 to 5.0 and at temperatures from 50 to 60oC. Flocculation was used for cell separation. Shifting the pH was more efficient than using polyelectrolytes, CaCl2, bentonite and Fe2O3. Recovery of inulinase by AOT(sodium di-2-ethylhexyl sulfosuccinate)-reversed micelles yielded up to ~20%.

The effect of pH (from 4.0 to 5.0), temperature (T) (from 30 oC to 40 oC) and dissolved oxygen concentration (DO) (from 0.2 to 6.0 mg O2/L) on glucose 6-phosphate dehydrogenase (G6PDH) (EC 1.1.1.49) and Invertase (EC 3.2.1.26) formation by S. cerevisiae were studied. The best culture conditions for G6PDH and Invertase formation were: 2.55 L culture medium (yeast extract, 3.0 g/L; 5peptone, 5.0 g/L; glucose, 2.0 g/L; sucrose, 15.0 g/L; Na2HPO4.12 H2O, 2.4 g/L; (NH4)2SO4, 5.1 g/L and MgSO4. 7H2O, 0.075 g/L); 0.45 L inoculum (0.70 g dry cell/L); pH = 4.5; T = 35 oC and DO = 4.0 mg/L. G6PDH was highly sensitive to pH, T and DO variation. The increase in G6PDH production was about three times when the DO ranged from 0.2 to 4.0 mg O2/L. Moreover, by shifting pH from 5.0 to 4.5 and temperature from 30 oC to 35 oC, G6PDH formation increased by 57% and 70%, respectively. Invertase activity (IA) of whole cells decreased at least 50% at extremes values of DO (2.0 and 6.0 mg O2/L) and pH (4.0 and 5.0). Furthermore, IA oscillated during the fermentation due to the glucose repression/derepression mechanism