Bioprocess and Biosystems Engineering

The recyclability of cellulase enzymes using zeolite and polyethylene glycol (PEG) was investigated. The cellulase enzymes from cellulose hydrolysate suspensions were adsorbed onto zeolite-β under typical working conditions (pH 5). PEG having a molecular weight of 200 Da and 20 kDa was used as an eluent to desorb the cellulase enzymes from zeolite-β. Adsorption and desorption profiles of cellulase enzymes were studied by varying pH, PEG concentration, and salt concentration. Maximum binding capacity, qm of the zeolite decreased by increasing the pH, or by introducing PEG. At pH 5, the qm of the zeolite was determined to be 121 × 10−3 g/g. About 24%, 51% and 75% of the adsorbed enzyme can be recovered using 1 M NaCl, PEG 200 and PEG 20000, respectively. The specific activity of the recovered enzyme increased by 57% due to the presence of residual PEG.

The introduction of an environmental stress of acidic pH shock had successfully solved the common deficiency existed in ε-PL production, viz. the distinct decline of ε-PL productivity in the feeding phase of the fed-batch fermentation. To unravel the underlying mechanism, we comparatively studied the physiological changes of Streptomyces sp. M-Z18 during fed-batch fermentations with the pH shock strategy (PS) and pH non-shock strategy (PNS). Morphology investigation showed that pellet-shape change was negligible throughout both fermentations. In addition, the distribution of pellet size rarely changed in the PS, whereas pellet size and number decreased substantially with time in the PNS. This was consistent with the performances of ε-PL productivity in both strategies, demonstrating that morphology could be used as a predictor of ε-PL productivity during fed-batch fermentation. Furthermore, a second growth phase happened in the PS after pH shock, followed by the re-appearance of live mycelia in the dead core of the pellets. Meanwhile, mycelia respiration and key enzymes in the central metabolic and ε-PL biosynthetic pathways were overall strengthened until the end of the fed-batch fermentation. As a result, the physiological changes induced by the acidic pH shock have synergistically and permanently contributed to the stimulation of ε-PL productivity. However, this second growth phase and re-appearance of live mycelia were absent in the PNS. These results indicated that the introduction of a short-term suppression on mycelia physiological metabolism would guarantee the long-term high ε-PL productivity.

To facilitate lipase (E.C.3.1.1.3) catalyzed hydrolysis reaction of triglycerides in heterogeneous reaction systems, lipase-surfactant complex (LSC) was prepared by mixing an aqueous solution of lipase and surfactant in ethanol. The LSC prepared from lipase MF-30 derived from Pseudomonas sp. and Nonion SP-60R (sorbitan mono-stearate) showed a high LSC yield and activity recovery. About 30% of the protein in the crude lipase was recovered in the LSC precipitate, and further addition of surfactant to the supernatant was ineffective. Our preparation method for the selective separation of the catalytic active protein from a crude enzyme was suggested.

This study examined a stirred-tank fermenter (STF) containing low-viscosity foaming liquids with an agitation impeller and foam-breaking impeller mounted on the same shaft. Results showed that the performance of the foam-breaking impeller can be improved by changing a conventional six-blade turbine impeller into a rod impeller as the agitation impeller. The volumetric oxygen-transfer coefficient, k L a, in the mechanical foam-control method (MFM) using a six-blade vaned disk as the foam-breaking impeller in the STF with the rod impeller was approximately five times greater than that of the chemical foam-control method (CFM) adding an anti-foaming agent in the STF with the six-blade turbine impeller. Application of the present method to the cultivation of Saccharomyces cerevisiae K-7 demonstrated that the cultivation time up to the maximum cell concentration was remarkably shorter than that achieved using a conventional CFM.

Polysaccharides produced by microorganisms are utilized for a variety of purposes, including the use in cosmetics and as food additives. More recently, polysaccharides have been exploited by the medical and pharmaceutical industries, and those originated from many species of mushrooms have been especially useful in industrial applications; however, the production and synthesis of these compounds is costly and time consuming. In this study, we developed a method for low-cost production of exopolysaccharide (EPS) that effectively screens components and optimizes medium composition using statistical methods (Plackett–Burman and Box–Behnken design). As a result, we obtained the following optimized medium: sucrose 165.73 g/L, sodium nitrate 3.08 g/L, dipotassium phosphate 1.00 g/L, potassium chloride 0.50 g/L, magnesium sulfate 0.50 g/L, ferrous sulfate 0.01 g/L, and 0.71 g/L of Ashbya gossypii extract. The maximum production of about 29 g/L EPS was achieved in the optimized medium during 84 h batch fermentation.

 The paper reports the measurement of biomass concentration using a laser turbidity probe. A suspension of Bakers’ yeast (0.5−50 gl-1) was subjected to various conditions of agitation and aeration in a stirred tank reactor and the turbidity measured using the probe. Both agitation and aeration were found to influence the turbidity. At any constant biomass concentration, the effect on the turbidity measurement of changing agitation or aeration rate independently was linear, while at any constant conditions of agitation and aeration rate, the relationship between turbidity and biomass concentration was non-linear. The results indicate that, in a bioprocess with non-particulate medium, it is possible to correct for the effects of aeration and agitation on turbidity measurement using a multivariate calibration model. A procedure for calibration and correction of measurements for the effects of agitation and aeration is presented and is verified using experimental data. This procedure may be generalised for other applications.

The production of monoglycerides by glycerolysis of olive oil catalyzed by lipases from Candida rugosa, Chromobacterium viscosum and Rhizopus sp. immobilized in a hydrophylic polyurethane foam was investigated. The effect of the amount of aqueous phase used for foam polymerization on the competing reactions of glycerolysis and hydrolysis was studied. The highest monoglyceride production was achieved with the C. rugosa lipase which was thus selected for subsequent studies. The extent to which hydrolysis and glycerolysis occur and the influence of the initial a w of the system on both reactions were also investigated. In glycerolytic reaction systems, initial rates of fatty acid release were always higher than in hydrolytic systems. At a w values lower than 0.43, hydrolysis was completely repressed, although glycerolysis still occurred. This suggests that hydrolysis of the ester bond in the glyceride, promoted by glycerol, is the first reaction step. In glycerolysis, initial rates of FFA and DG production increased exponentially with the initial a w of the system. The lowest total conversion (in terms of % TG consumed) at 48 hours was obtained at intermediate a w values; higher conversions at extreme a w indicated an increase in hydrolytic and glycerolytic rates, at high and low a w respectively. The yield of MG increased with decreasing a w . The highest yield of MG (∼70%, w/w) was obtained at the lowest a w used (0.23). The initial a w of the reaction system is an important parameter in glycerolysis.

In this study, we discussed the development and optimization of an intensified CHO culture process, highlighting medium and control strategies to improve lactate metabolism. A few strategies, including supplementing glucose with other sugars (fructose, maltose, and galactose), controlling glucose level at <0.2 mM, and supplementing medium with copper sulfate, were found to be effective in reducing lactate accumulation. Among them, copper sulfate supplementation was found to be critical for process optimization when glucose was in excess. When copper sulfate was supplemented in the new process, two-fold increase in cell density (66.5 ± 8.4 × 106 cells/mL) and titer (11.9 ± 0.6 g/L) was achieved. Productivity and product quality attributes differences between batch, fed-batch, and concentrated fed-batch cultures were discussed. The importance of process and cell metabolism understanding when adapting the existing process to a new operational mode was demonstrated in the study.