Check out our New Publishers' Select for Free Articles

Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.97, #2)

Use of glucose feeding to produce concentrated yeast cells by Beth H. Junker; Zorina Mann; Anna Seeley; Jinyou Zhang; Randolph Greasham (pp. 63-78).

A defined medium and fed-batch feeding process for the production of a yeast biocatalyst, developed at the 23-L scale, was scaled up to the 600-L pilot scale. Presterilized 100-L-vol plastic bags were implemented for the pilotscale nutrient feeding. Medium of increased concentration Ôqs implemented at the pilot scale, and equivalent dry cell weights were reached with a medium 80% more concentrated than that used at the laboratory scale. The higher medium concentration was believed to be necessary at the pilot scale owing to the additional heat stresses on key components (e.g., complexing of magnesium sulfate with phosphate), increased dilution during sterilization, lower evaporation rate owing to the lower vessel volume per minute air flow rate, and increased dilution owing to nutrient feeding or shot additions. Peak cell density was found to be somewhat insensitive to variations in residual glucose levels. These results suggest that defined medium developed at the laboratory scale may need to be further optimized at the pilot scale for equivalent performance.

Keywords: Fed batch; disposable sterile bag; yeast; cell mass; defined medium

Adsorptive immobilization of intestinal brush border membrane on triton X-100-substituted sepharose 4B by Mehran Habibi-Rezaei; Mohsen Nemat-Gorgani (pp. 79-90).

Triton X-100-substituted Sepharose 4B (Sepharose-TX) was used for adsorptive immobilization of intestinal brush border membrane using lactose-phlorizin hydrolase as a representative membrane enzyme. Limited heating of membrane preparations was found to enhance binding. This enhancement is concluded to be owing to a greater availability of the hydrophobic sites, as also confirmed by the 1-anilino-8-naphthalene sulfonate fluorescence studies, for interaction with Triton X-100 moieties on the support. The immobilized preparations obtained by this procedure were found useful in hydrolysis of lactose, involving lactose-phlorizin hydrolase, in continuous operations. It is suggested that the approach may be of general utility for immobilization of biologic membranes by interaction of their extramembrane structures using supports with appropriate hydrophobic groups.

Keywords: Adsorption; continuous operation; ectoprotein; intestinal brush border membrane; lactase-phlorizin hydrolase; molten globule

Fenton’s reagent-mediated degradation of residual Kraft black liquor by Elisa Araujo; Antonio J. Rodríguez-Malaver; Aura M. González; Orlando J. Rojas; Nancy Peñaloza; Johnny Bullón; Mayra A. Lara; Natalia Dmitrieva (pp. 91-103).

In this work, the effect of Fento’s reagent on the degradation of residual Kraft black liquor was investigated. The effect of Fenton’s reagent on the black liquor degradation was dependent on the concentration of H₂O₂. At low concentrations (5 and 15 mM) of H₂O₂, Fenton’s reagent caused the degradation of phenolic groups (6.8 and 44.8%, respectively), the reduction of reaction medium pH (18.2%), and the polymerization of black liquor lignin. At a high concentration (60 mM) of H₂O₂, Fenton’s reagent induced an extensive degradation of lignin (95–100%) and discoloration of the black liquor. In the presence of traces of iron, the addition of H₂O₂ alone induced mainly lignin fragmentation. In conclusion, Fenton’s reagent and H₂O₂ alone can degrade residual Kraft black liquor under acidic conditions at room temperature.

Keywords: Fenton’s reagent; free radicals; hydrogen peroxide; hydroxyl radical; Kraft black liquor; lignin degradation; pulp mill effluent treatment

Low-temperature brewing by freeze-dried immobilized cells by Argyro Bekatorou; Magda J. Soupioni; Athanasios A. Koutinas; Maria E. Kanellaki (pp. 105-121).

We propose a novel biocatalyst in brewing. A cryotolerant strain of Saccharomyces cerevisiae was immobilized on delignified cellulosic material followed by freeze-drying of the immobilized cells without the use of any cryoprotectant. The freeze-dried immobilized biocatalyst was used in repeatedbatch fermentation of wort and showed reduced fermentation time and increased productivities as compared with free freeze-dried cells (FFDCs). It also demonstrated suitability for low-temperature brewing (5 and 0°C). The fermentation time in repeated-batch fermentations at 15°C was 1.5–2 d for a period of 13 mo, showing a high operational stability of the system. At 0°C the freeze-dried immobilized biocatalyst showed a 2- to 3.5-fold decrease in fermentation time in comparison with FFDCs. Polyphenol contents, bitterness, and diacetyl concentration were lower in beers produced by freezedried immobilized cells as compared with FFDCs. At 0°C polyphenols were 40% lower than at 15°C. Higher alcohols were reduced and ethyl acetate increased in comparison with FFDCs. Amyl alcohols at 0°C were lower than half of their content at 15°C, while ethyl acetate was 31 mg/L at 0°C and 18 mg/L at 15°C. These data justify the improved aroma and taste of beers produced by freeze-dried immobilized biocatalyst mainly at low temperatures.

Keywords: Brewing; freeze drying; immobilized cells; low temperature; fermentation

Characterization of a kerationlytic metalloprotease from Bacillus sp. SCB-3 by H. Lee; D. B. Suh; J. H. Hwang; H. J. Suh (pp. 123-133).

A keratinolytic protease-producing microorganism was isolated from soybean paste waste and was identified as a strain of Bacillus sp. The keratinase was purified by polyethylene glycol precipitation and two successive column chromatographies with DEAE-Toyopearl 650C and Sephacryl S-200 HR. The purified enzyme had overall 11 purification folds with an 18% yield. The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration on Sephacryl G-200 indicated that the purified enzyme was monomeric and had a molecular weight of 134 kDa. The optimum temperature and pH were 40°C and 7.0, respectively. This enzyme was completely inhibited by EDTA and EGTA, and it was restored by the addition of Ca⁺² and Mg⁺². These results suggested that it is a metalloprotease. The stimulated enzyme activity by reducing agents indicated that the reducing condition was important in the expression of the activity.

Keywords: Bacillus sp.; metalloprotease; keratinolytic activity

Overexpression in Catharanthus roseus hairy roots of a truncated hamster 3-hydroxy-3-methylglutaryl-CoA reductase gene by Teresa Ayora-Talavera; Joseph Chappell; Edmundo Lozoya-Gloria; Victor M. Loyola-Vargas (pp. 135-145).

Catharanthus roseus (L.) G. Don hairy roots harboring hamster 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) (EC 1.1.1.88) cDNA without membrane-binding domain were evaluated by quantifying the levels of sterols and some indol-alkaloids. Clone 236, with the highest hybridization signal, had the lowest soluble and microsomal HMGR activity and produced more ajmalicine and catharanthine than the control but had reduced campesterol concentration. Clone 19, with low hybridization signal, had high soluble HMGR activity and produced high levels of campesterol and five to seven times more serpentine than the control but a low level of ajmalicine and no accumulation of catharanthine. These results suggest a possible role for HMGR in indole alkaloid biosynthesis and a possible cosuppression of both the endogenous and foreign HMGR genes in clone 236.

Keywords: Alkaloids; Catharanthus roseus ; hairy roots; 3-hydroxy-3-methylglutaryl-CoA reductase

Sections

Personal tools

Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.97, #2)

Sections

Personal tools

Local resources

Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.97, #2)