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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.112, #1)
Development of supporting materials for microbial immobilization and iron oxidation by Hyo-Jin Son; Yang-Ho Park; Jung-Heon Lee (pp. 1-12).
We developed the microbial immobilization particle with curdlan and activated carbon, which has great adsorption capacity. The characteristics of porosity and mechanical strength of these supporting particles are dependent on manufacturing method. The supporting particle showed the best performance when the ratio of curdlan and activated carbon was 30 to 6 g/L. Brumauer-Emmett-Teller (specific surface area) and swelling capacity of the carrier were 52.63 m2/g and 17 (w/w), respectively. The immobilization characteristics of iron-oxidizing bacteria on supporting particles were observed using a scanning electron microscope. The concentration of micro-organism on the surface of supporting particle was increased with reaction time. As the number of iron oxidation batch cycles increased, the iron oxidation rate increased.
Keywords: Curdlan; supporting particle; microbial immobilization; H2S removal
Alkaline peroxide mechanical pulping of wheat straw with enzyme treatment by Jian Zhao; Xuezhi Li; Yinbo Qu; Peiji Gao (pp. 13-23).
Alkaline peroxide mechanical pulping (APMP) of wheat straw with enzyme treatment was studied. Instead of direct enzyme pretreatment on wheat straw, an alternative treatment method was used, in which coarse pulps from refiner defibrated wheat straw rather than wheat straw were pretreated with a crude enzyme containing mainly xylanase, then impregnated with alkaline H2O2 solution and further refined. The optimum conditions of enzyme treatment were xylanase dosage of 10–15 IU/g of oven-dried wheat straw, 90 min, 50–60°C, pulp consistency of 5–10%, and initial pH of 5.0, and those for chemical impregnation were 6% NaOH, 70–80°C, 60–90 min, and 4 to 5% H2O2. Enzyme treatment improved pulpability of wheat straw by the APMP process, and final pulp quality such as brightness, breaking length, and burst index of pulp. Pulp from the APMP process with enzyme treatment could be bleached to a brightness of 70.5% ISO by two-stage H2O2 bleaching sequence with only 4% H2O2, and breaking length of the bleach pulp reached 4470 m.
Keywords: Alkaline peroxide mechanical pulping; enzyme treatment; impregnation; bleaching; wheat straw
High-temperature wine making using the thermotolerant yeast strain Kluyveromyces marxianus IMB3 by Y. Kourkoutas; C. McErlean; M. Kanellaki; C. J. Hack; R. Marchant; I. M. Banat; A. A. Koutinas (pp. 25-35).
Kluyveromyces marxianus IMB3 yeast cells were immobilized on delignified cellulosic material, apple, and quince separately. Both immobilized and free cells were used in high-temperature wine making, and their fermented grape must contained 3 to 4% alcohol. Semisweet wines were produced by the addition of potable alcohol to the fermented must. Preliminary sensory evaluation of the produced semisweet wines showed good flavor and aroma. The final product contained extremely low levels of higher and amyl alcohols while ethyl acetate was at levels usually present in wines. The ferment produced may be blended with other products to improve their quality.
Keywords: Wine making; high temperature; immobilized cells; volatile byproducts; fermentation
Production of β-carotene from beet molasses by Blakeslea trispora in stirred-tank and bubble column reactors by Yekta Goksungur; Fani Mantzouridou; Triantafyllos Roukas; Parthena Kotzekidou (pp. 37-54).
The effect of aeration rate and agitation speed on β-carotene production from molasses by Blakeslea trispora in a stirred-tank fermentor and optimization of the production of the pigment in a bubble column reactor were investigated. In addition, a central composite design was employed to determine the maximum β-carotene concentration at optimum values for the process variables (aeration rate, sugar concentration, linoleic acid, kerosene). By image analysis of the morphology of the fungus, a quantitative characterization of the hyphae and zygospores formed was obtained. The hyphae were differentiated to intacthyphae, vacuolated hyphae, evacuated cells and degenerated hyphae. An increased proportion of zygospores was correlated to high β-carotene production. In the stirred-tank fermentor, the highest concentration of the carotenoid pigment (92.0 mg/L) was obtained at an aeration rate of 1.5 vvm and agitation speed of 60 rpm. In the bubble column reactor, the aeration rate and concentration of sugars, linoleic acid, kerosene, and antioxidant significantly affected the production of β-carotene. In all cases, the fit of the model was found to be good. Aeration rate, sugar concentration, linoleic acid, and kerosene had a strong positive linear effect on β-carotene concentration. Moreover, the concentration of the pigment was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions. Maximum β-carotene concentration (360.2 mg/L) was obtained in culture grown in molasses solution containing 5% (w/v) sugar supplemented with linoleic acid (37.59 g/L), kerosene (39.11 g/L), and antioxidant (1.0 g/L).
Keywords: β-carotene; beet molasses; Blakeslea trispora ; stirred-tank fermentor; bubble column reactor; response surface methodology
Lipase-catalyzed solvent-free transesterification of wood sterols by Irene Martínez; Alejandro Markovits; Rolando Chamy; Andrés Markovits (pp. 55-62).
Eighteen commercial lipase preparations, either immobilized or crude enzyme powders, were screened for the transesterification of wood sterols. The reactions were carried out in a solvent-free system, at the optimum temperature of the enzyme preparations as reproted by the manufacturer and at the pressure of 2 mbar, with 5 or 10% in weight of the enzyme relative to the wood sterol content of the reacting mixture. Methyl esters of sunflower fatty acids were used as transesterifying agent. Of all the enzymes assayed, only Lipase TL from Pseudomonas stutzeri PL-836 (Meito Sangyo) exhibited any significant transesterifying capacity, 85 and 95% of conversion after 2 and 8 h of reaction, respectively, when 10% in weight of enzyme was used.
Keywords: Enzymatic transesterification; lipase; sterols; steryl esters; solvent-free system