Extractive bioconversions in aqueous two-phase systems: enzymatic hydrolysis of casein proteins

Partition coefficients in poly(ethylene glycol)/dextran aqueous two-phase systems are reported for mixed-casein and its components, alpha, beta and kappa casein. Rates of casein proteolysis by alpha-chymotrypsin and by trypsin are reported in single-phase and aqueous two-phase reactor systems. The advantages resulting from selective partitioning of substrates, enzymes, and products are examined in terms of relative volumetric reaction rates.     

Improvement of the yield of physiologically active oligosaccharides in continuous hydrolysis of chitosan using immobilized chitosanases

The continuous production of chitosan oligosaccharides using a packed-bed enzyme reactor was investigated as to the effects of the operation conditions on the yield of pentamers and hexamers of chitosan oligosaccharides. A column reactor packed with immobilized chitosanases prepared by the multipoint attachment method was used for continuous hydrolysis of chitosan. In this reactor, the decrease of the yield of the target intermediate oligosaccharides due to axial mixing was negligible. The surface enzyme density of the support and flow rate of the substrate solution significantly affected the maximum yield of pentamers and hexamers. These effects were summarized as a correlation with the Damk?hler number (Da), defined as the ratio of the maximum reaction rate to the maximum mass transfer rate. The optimum condition was determined based on Da. Under the optimized condition (Da = 0.12), pentamers and hexamers could be produced continuously for a month with a yield of over 35% (7 kg/m(3) in concentration).     

Factors affecting the composition of oligosaccharides produced in chitosan hydrolysis using immobilized chitosanases

The hydrolysis reaction of chitosan using immobilized chitosanases with regard to the composition of its products and the yield of the intermediate target products, pentamer and hexamer of chitosan oligosaccharides, was investigated. Chitosanase was immobilized onto agar or agarose gel particles by the multipoint attachment method. In batch experiments, surface enzyme density, support particle size, temperature, agitator speed, and initial substrate concentration significantly affected the composition of the oligosaccharides produced. It was believed that these factors all related to the reaction rate and mass transfer rate at the surface of the support materials immobilizing the enzymes. These effects were summarized as a correlation with Damk?hler number (Da), defined as the ratio of the maximum reaction rate to the maximum mass transfer rate. The result showed that the reaction conditions that give a low value of Da provide a high yield of pentamer and hexamer oligosaccharides.     

Protection of bioreactor from microbial contamination by high dissolved oxygen tension

Summary Repeated batch hydrolysis of casein using immobilized protease were carried out at various do tensions and pH. At any of the pH tested, microbial contamination could be satisfactorily suppressed by maintaining high do. In continuous reaction, contamination could be suppressed throughout 40 days under the do of 190 ppm, whereas contamination was observed after 24 hours with the do of 2.5 ppm.     

Effects of periodic change in pressure and dissolved-oxygen concentration on the incubation characteristics of Pseudomonas aeruginosa

Experiments were carried out to identify an efficient procedure for decreasing the amount of excess sludge in deep aeration columns. Incubation characteristics, especially cellular yield, are closely related to excess sludge, maximum specific growth rate, and chemical oxygen demand. They were measured here for the bacterium Pseudomonas aeruginosa, which tends to be predominant in sewage treatment, at a pressure remaining constant or periodically changing in the range of 1-6 atm (abs.). Cellular yields tended to decrease over 1-2 min pressure cycles; in steady operation they decreased considerably with increasing pressure or dissolved oxygen concentration. Maximum specific growth rates were moderately affected by periodic changes in pressure or dissolved oxygen concentration but markedly affected in the higher concentration range under steady operation. Substrate consumption rates on the other hand, were little affected in either case. The values of chemical oxygen demand ranged from 220 to 250 mg/L, and were thus nearly constant.     

Variation in cellulase-constituting components from Trichoderma reesei with agitation intensity

Cellulase producing activity of Trichoderma reesei QM9414 was examined under various agitation intensities and at the dissolved oxygen concentration above 3 ppm. The producing activity greatly depended upon the agitation intensity, and the dependence on the agitation was different for each cellulase-constituting component. The maximum producing activities of FPA, CM Case, and beta-glucosidase were obtained under different agitation conditions, 1.0, 0.7, and 1.4 m/s in tip velocity, respectively. Intensive agitation brought about remarkable reduction in all cellulase components. The mycelial transformation through agitation intensity was also observed. Comparatively mild agitation of 0.3-1.0 m/s caused pellet formation as the culture progressed, although the pelletization was delayed with increasing agitation intensity. The behavior of the pelletization did not occur at 1.3 and 1.7 m/s throughout the course of cultivation, and under the latter agitation condition hyphae were broken up into short fragments. The cellulase producing activity is discussed in relation to such morphological changes.     

Selective and stable production of physiologically active chitosan oligosaccharides using an enzymatic membrane bioreactor

We investigated the production of chitosan oligosaccharides by continuous hydrolysis of chitosan in an enzyme membrane bioreactor, with the goal of improving the yield of physiologically active oligosaccharides (pentamers and hexamers) and achieving operational stability. The bioreactor was a continuous-flow stirred-tank reactor equipped with an ultrafiltration membrane with a molecular weight cut-off of 2000 Da, and the hydrolysis was accomplished with chitosanase from Bacillus pumilus. After optimization of the reaction parameters, such as the amount of enzyme, the yield of the target oligosaccharides produced in the membrane bioreactor with free chitosanase reached 52% on the basis of the fed concentration of chitosan. An immobilized chitosanase prepared by the multipoint attachment method was used to improve the operational stability of the membrane bioreactor. Under the optimized conditions, pentameric and hexameric chitosan oligosaccharides were steadily produced at 2.3 g/L (46% yield) for a month. The half-life of the productivity of the reactor was estimated to be 50 d under the conditions examined.     

Transesterification reaction between medium- and long-chain fatty acid triglycerides using surfactant-modified lipase

Transesterification between medium-chain fatty acid triglycerides (MCT) and long-chain fatty acid triglycerides (LCT) in a nonsolvent system was investigated using surfactant modified lipase which is a complex of lipase, Rhizopus japonicus and surfactant, sorbitan monostearate. 74% conversion of was obtained after a 48-h reaction period, and the triglyceride composition was well described by the 1, 3-random 2-random stochastic model. The transesterification reaction between MCT and LCT closely followed the simple kinetic model, and the change in MCT and LCT contents could be simulated using one parameter. The effects of the water activity (A(w)) of modified lipase, the water content of the reaction system and the reaction temperature on the reaction rate were studied. A modified lipase A(w) of 0.35 and a water content of the reaction system at 0.09 wt % showed the highest activity. Inactivation did not occur below 60 degrees C, however, the activity decreased at temperatures over 70 degrees C.