Process biochemistry

... The use of starter cultures in the fermentation of boza, a traditional Turkish beverage. Murat Zorba a , Omre Hancioglu a , Mahmut Genc a , Mehmet Karapinar Corresponding Author Contact Information , a , E-mail The Corresponding Author and Gulden Ova a. ...

The production of laccase by Trametes versicolor in airlift bioreactors was studied. In order to enhance laccase production several inducers were tested, among which 2,5-xylidine led, by far, to the highest activities (around 1500 U/l). The bioreactor operated in two successive batches for 40 days with no operational problems and pellets of regular size were maintained throughout the fermentation. The bioreactor configuration employed is appropriate for laccase production by free cells of T. versicolor. The extracellular liquid obtained was studied in terms of pH and temperature activity and stability. The ligninolytic fluid produced was fully active at pH 3 and 60 °C. Moreover, it was stable at pH 5 and retained about 70% activity at 30 °C for 12 days. In addition, it was able to decolourise the sulphonephthalein dye Phenol Red. This decolourisation was most efficient at pH 5.

Whole cells of bakers’ yeast (Saccharomyces cerevisiae) exhibited very low catalase activity (16 U g−1). Various treatments altered membrane permeability and increased cellular catalase activity. Treatment with cetyltrimethylammonium bromide (CTAB) yielded maximum catalase activity (51000 U g−1) followed by digitonin (27072 U g−1). After permeabilization of the membrane, the catalase slowly leaks out of the cells. The half-life of intracellular catalase in CTAB-permeabilized cells was 3.4 days at 4°C and 1.2 days at 26°C. Catalase in permeabilized cells was more stable against self-inactivation during catalysis than the enzyme in cell-free extract and purified catalase. Catalase of CTAB-permeabilized cells was effective in removing the residual H2O2 from H2O2-treated fresh milk/heat pasteurized milk.

A process for producing non-monosaccharide and high-purity galactooligosaccharides (GOS) was proposed. GOS were produced from lactose by Penicillium expansum F3 β-galactosidase immobilized in calcium alginate. The effects of pH, temperature and lactose concentration on GOS production were investigated. A purity of 28.7% (w/w) GOS was obtained from 380 g/L lactose solution at pH 5.4 and 50 °C. The immobilized enzyme was used for repeated GOS synthesis and showed good operational stability. Digestible sugars in the GOS could be depleted after fermentation with Saccharomyces cerevisiae L1 or Kluyveromyces lactis L3 entrapped in the calcium alginate. Purity greater than 37% with yields greater than 27% of non-monosaccharide GOS were maintained by S. cerevisiae L1 for 19 batches and purity greater than 97% with a yield greater than 20% of high-purity GOS was produced using K. lactis L3 for two batches.

A sequencing batch reactor (SBR) has certain advantages over conventional activated sludge processes (ASP) for the treatment of complex wastewater. The performance of a sequencing batch reactor in treating complex chemical effluents was investigated with a suspended biomass configuration and operating under aerobic conditions. A total sequence of 24 h (15 min: filling phase; 23 h: reaction phase (aeration with recirculation); 30 min: setting; and 15 min: withdrawal) was employed and studied with various organic loading rates (1.0 kg COD/m3/day: 1.7 kg COD/m3/day and 3.5 kg COD/m3/day). The SBR performance was assessed by means of carbon removal and operational parameters such as pH, oxidation–reduction potential (ORP), sludge volume (SV), sludge volume index (SVI), suspended solids (SS) and volatile suspended solids (VSS), which were monitored during reactor operation. The SBR showed relatively more efficient performance over conventional suspended growth systems. About 8% sulphate was removed under anoxic conditions at all the studied organic loading rates. Enhanced performance with SBR over conventional ASP may be due to enforced short term unsteady state conditions coupled with periodic exposure of the microorganisms (physiological state) to defined process conditions which facilitate the required metabolic conditions for treating complex chemical effluents.