Influence of airflow intensity on phytase production by solid-state fermentation.

Phytase production by Aspergillus niger F3 by solid state fermentation (SSF) on citrus peel was evaluated at pilot scale under different aeration conditions. The best airflow intensity was 1 VkgM (Lair kg medium(-1) min(-1)), which allowed to produce 65 units of phytases per gram in dry basis (65 Ug(-1) d.b.) as it removed the metabolic heat generated by the microorganism, Agitation did not improve heat removal. Airflow intensity was considered as scale-up criterion. When the airflow intensity was maintained at 1 VkgM for SSF with 2 and 20 kg of medium, the kinetics parameters for biomass and enzyme concentration at the end of fermentation differed by less than 2. The air flow intensity was required to maintain the temperature and cool the SSF and to provide oxygen for microbial growth. Air flow intensity is a key a factor that must be considered when scale-up of SSF is attempted.

The behavior of kinetic parameters in production of pectinase and xylanase by solid-state fermentation.

Solid-state fermentation (SSF) is defined as the growth of microbes without a free-flowing aqueous phase. The feasibility of using a citrus peel for producing pectinase and xylanase via the SSF process by Aspergillus niger F3 was evaluated in a 2 kg bioreactor. Different aeration conditions were tested to optimize the pectinase and xylanase production. The best air flow intensity was 1 V kg M (volumetric air flow per kilogram of medium), which allowed a sufficient amount of O2 for the microorganism growth producing 265 U/g and 65 U/g pectinases and xylanases, respectively. A mathematical model was applied to determine the different kinetic parameters related to SSF. The specific growth rate and biomass oxygen yield decreased during fermentation, whereas an increase in the maintenance coefficient for the different employed carbon sources was concurrently observed.

Packed bed column fermenter and kinetic modeling for upgrading the nutritional quality of coffee husk in solid-state fermentation.

Studies were carried out to evaluate solid-state fermentation (SSF) for the upgradation of the nutritional quality of coffee husk by degrading the caffeine and tannins present in it. SSF was carried out by Aspergillus niger LPBx in a glass column fermenter using factorial design experiments and surface response methodology to optimize bioprocess parameters such as the substrate pH and moisture content and aeration rate. The first factorial design showed that the moisture content of the substrate and aeration rate were significant factors for the degradation of toxic compounds, which was confirmed by the second factorial design too. The kinetic study showed that the degradation of toxic compounds was related to the development of the mold and its respiration and also to the consumption of the reducing sugars present in coffee husk. From the values obtained experimentally for the oxygen uptake rate and CO(2) evolved, the system determined a biomass yield (Y(x/o)) of 3.811 (g of biomass).(g of consumed O(2))(-1) and a maintenance coefficient (m) of 0.0031 (g of consumed O(2)).(g biomass of biomass)(-1).h(-1). The best results on the degradation of caffeine (90%) and tannins (57%) were achieved when SSF was carried out with a 30 mL.min(-1) aeration rate using coffee husk having a 55% initial moisture content. The inoculation rate did not affect the metabolization of the toxic compounds by the fungal culture. After SSF, the protein content of the husk was increased to 10.6%, which was more than double that of the unfermented husk (5.2%).

Production, purification and properties of microbial phytases.

Phytases (myo-inositol hexakisphosphate phosphohydrolase, EC 3.1.3.8) catalyse the release of phosphate from phytate (mycoinositol hexakiphosphate). Several cereal grains, legumes and oilseeds, etc., store phosphorus as phytate. Environmental pollution due to the high-phosphate manure, resulting in the accumulation of P at various locations has raised serious concerns. Phytases appear of significant value in effectively controlling P pollution. They can be produced from a host of sources including plants, animals and micro-organisms. Microbial sources, however, are promising for their commercial exploitations. Strains of Aspergillus sp., chiefly A. ficuum and A. niger have most commonly been employed for industrial purposes. Phytases are considered as a monomeric protein, generally possessing a molecular weight between 40 and 100 kDa. They show broad substrate specificity and have generally pH and temperature optima around 4.5-6.0 and 45-60 degrees C. The crystal structure of phytase has been determined at 2.5 A resolution. Immobilization of phytase has been found to enhance its thermostability. This article reviews recent trends on the production, purification and properties of microbial phytases.

[Kinetic study of prostaglandin biosynthesis. A mathematical model]. / Kineticheskoe issledovanie biosinteza prostaglandinov. Matematicheskaia model'.

A mathematical model has been suggested to describe the kinetics of the prostanoid biosynthesis in the Plexaura homomalla coral. It allows to predict the changes in prostaglandin A2 concentration at various pH and concentration of sodium ions citrate when the latter is not too high. The degradation of prostaglandin biosynthesis intermediates is shown to proceed as two consecutive first-order reactions. For the second step the reaction rate grows into the raise of prostaglandin A2 concentration, apparently due to autocatalytic character of the process.