Dried–Reswollen Immobilized Biocatalysts for Detoxification of Organophosphorous Compounds in the Flow Systems

New immobilized biocatalysts based on polypeptides containing N- or C-terminal polyhistidine sequences and possessing organophosphorus hydrolase activity were investigated for detoxification of organophosphorous neurotoxic compounds in the flow systems. The biocatalysts were revealed to have a high catalytic activity within wide pH and temperature ranges 7.5–12.5 °C and 15–65 °C, respectively. The immobilized biocatalysts can be dried and reswollen before use with 92–93% catalytic activity remaining after drying and rehydration procedures. The half-lives of the biocatalysts under wet and dry storage conditions were 420 and 540 days, respectively.     

Thermal Drying of <Emphasis Type="BoldItalic">Lactobacillus delbrueckii</Emphasis> subsp. <Emphasis Type="BoldItalic">bulgaricus</Emphasis> and its Efficient Use as Starter for Whey Fermentation and Unsalted Cheese Making

Lactobacillus bulgaricus grown on whey was dried by a simple thermal drying method at the range 35–55°C and its efficiency for lactic acid fermentation of whey was evaluated. Drying of cells in whey suspension in the examined temperature range did not affect significantly their viability (82–87% survival), indicating a protective effect of whey as both growth and drying medium. The kinetics of fermentation of whey and mixtures of whey/molasses using the dried culture were comparable to those of non-dried cells, and only low pH had a detrimental effect on the fermentation ability of the dried cells. Furthermore, dried L. bulgaricus, free or immobilized on casein coagulates, was used as starter for the production of unsalted hard-type cheese. The effects of the amount of starter culture and the immobilization technique, the evolution of microbial counts, and the sensory properties of the produced cheeses were evaluated during ripening at various temperatures.     

Novel Technology Development through Thermal Drying of Encapsulated Kluyveromyces marxianus in Micro- and Nano-tubular Cellulose in Lactose Fermentation and Its Evaluation for Food Production

A novel technology development based on the production of a low-cost starter culture for ripening of cheeses and baking is reported in the present study. The starter culture comprises thermally dried cells of Kluyveromyces marxianus encapsulated in micro- and nano-tubular cellulose. For production of a low-cost and effective biocatalyst, whey was used as raw material for biomass production and thermal drying methods (convective, conventional, and vacuum) were applied and evaluated at drying temperatures ranging from 35 to 60?°C. The effect of drying temperature of biocatalysts on fermentability of lactose and whey was evaluated. Storage stability and suitability of biocatalysts as a commercial starter cultures was also assessed and evaluated. All thermally dried biocatalysts were found to be active in lactose and whey fermentation. In all cases, there was sugar conversion ranging from 92 to 100?%, ethanol concentration of up to 1.47?% (v/v), and lactic acid concentrations ranged from 4.1 to 5.5?g/l. However, convective drying of the encapsulated cells of K. marxianus in micro- and nano-tubular cellulose was faster and a more effective drying method while drying at 42?°C appear to be the best drying temperature in terms of cell activity, ethanol, and lactic acid formation. Storage of the biocatalysts for 3?months at 4?°C proved maintenance of its activity even though fermentation times increased by 50?C100?% compared with the fresh dried ones.     

Low-temperature brewing by freeze-dried immobilized cells

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.     

Dry Red Wine Making Using Yeast Immobilized on Cork Pieces

The commercial Saccharomyces cerevisiae Uvaferme 299 wine yeast was immobilized on cork pieces to produce a biocatalyst for use in dry red wine making. The immobilized biocatalyst was suitable for clarified and non-clarified grape must fermentation at ambient and low temperatures (0–25 °C). Fermentation times were low and very low amounts of residual sugar were detected, showing suitability for dry wine production. The presence of suspended solids in the non-clarified must did not affect the activity of the immobilized cells. Complete fermentation of sugars at 0 °C was possible with immobilized Uvaferme 299, although not a cryotolerant strain, indicating a cryoprotective effect of cork. The presence of cork did not affect the composition of major volatiles with methanol and acetaldehyde kept at low levels. Reduction of amyl alcohols on total volatiles was also observed in wines fermented at low temperatures. Differences in the headspace aroma profile in wines produced by immobilized and free cells were found by GC–MS analysis, but no cork taint compounds were detected.     

Lactose Hydrolysis by β-Galactosidase Covalently Immobilized to Thermally Stable Biopolymers

Lactose has been hydrolyzed using covalently immobilized β-galactosidase on thermally stable carrageenan coated with chitosan (hydrogel). The hydrogel’s mode of interaction was proven by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and Schiff’s base formation. The DSC thermogram proved the formation of a strong polyelectrolyte complex between carrageenan and chitosan followed by glutaraldehyde as they formed one single peak. The modification of carrageenan improved the gel’s thermal stability in solutions from 35 °C to 95 °C. The hydrogel has been proven to be efficient for β-galactosidase immobilization where 11 U/g wet gel was immobilized with 50% enzyme loading capacity. Activity and stability of free and immobilized β-galactosidase towards pH and temperature showed marked shifts in their optimum pH from 4.5–5 to 5–5.5 and temperature from 50 °C to 45–55 °C after immobilization, which reveals higher catalytic activity and reasonable stability at wider pHs and temperatures. The apparent K _m of the immobilized enzyme increased from 13.2 to 125 mM, whereas the V _max increased from 3.2 to 6.6 μmol/min compared to the free enzyme, respectively. The free and immobilized enzymes showed lactose conversion of 87% and 70% at 7 h, respectively. The operational stability showed 97% retention of the enzyme activity after 15 uses, which demonstrates that the covalently immobilized enzyme is unlikely to leach. The new carrier could be suitable for immobilization of other industrial enzymes.     

Immobilization of Naringinase in PVA–Alginate Matrix Using an Innovative Technique

A synthetic polymer, polyvinyl alcohol (PVA), a cheap and nontoxic synthetic polymer to organism, has been ascribed for biocatalyst immobilization. In this work PVA–alginate beads were developed with thermal, mechanical, and chemical stability to high temperatures (<80 °C). The combination of alginate and bead treatment with sodium sulfate not only prevented agglomeration but produced beads of high gel strength and conferred enzyme protection from inactivation by boric acid. Naringinase from Penicillium decumbens was immobilized in PVA (10%)–alginate beads with three different sizes (1–3 mm), at three different alginate concentrations (0.2–1.0%), and these features were investigated in terms of swelling ratio within the beads, enzyme activity, and immobilization yield during hydrolysis of naringin. The pH and temperature optimum were 4.0 and 70 °C for the PVA–alginate-immobilized naringinase. The highest naringinase activity yield in PVA (10%)–alginate (1%) beads of 2 mm was 80%, at pH 4.0 and 70 °C. The Michaelis constant (K _Mapp) and the maximum reaction velocity (V _maxapp) were evaluated for both free (K _Mapp = 0.233 mM; V _maxapp = 0.13 mM min⁻¹) and immobilized naringinase (K _Mapp = 0.349 mM; V _maxapp = 0.08 mM min⁻¹). The residual activity of the immobilized enzyme was followed in eight consecutive batch runs with a retention activity of 70%. After 6 weeks, upon storage in acetate buffer pH 4 at 4 °C, the immobilized biocatalyst retained 90% of the initial activity. These promising results are illustrative of the potential of this immobilization strategy for the system evaluated and suggest that its application may be effectively performed for the entrapment of other biocatalysts.     

Effect of composition,solvent exchange liquid and drying method on the porous structure of phenol–formaldehyde gels

Organic gels have been synthesized by sol–gel polycondensation of phenol (P) and formaldehyde (F) catalyzed by sodium carbonate (C). The effect of synthesis parameters such as phenol/catalyst ratio (P/C), solvent exchange liquid and drying method, on the porous structure of the gels have been investigated. The total and mesopore volumes of the PF gels increased with increasing P/C ratio in the range of P/C ≤ 8, after this both properties started to decrease with P/C ratio for P/C > 8 and the gel with P/C = 8 showed the highest total and mesopore volumes of 1.281 and 1.279 cm³ g⁻¹ respectively. The gels prepared by freeze drying possessed significantly higher porosities than the vacuum dried gels. The pore volume and average pore diameter of the freeze dried gels were significantly higher than those of the vacuum dried gels. T-butanol emerged as the preferred solvent for the removal of water from the PF hydrogel prior to drying, as significantly higher pore volumes and specific surface areas were obtained in the corresponding dried gels. The results showed that freeze drying with t-butanol and lower P/C ratios were favourable conditions for the synthesis of highly mesoporous phenol–formaldehyde gels.     

Impact of High Temperature on Ethanol Fermentation by Kluyveromyces marxianus Immobilized on Banana Leaf Sheath Pieces

Ethanol fermentation was carried out with Kluyveromyces marxianus cells at various temperatures (30, 35, 40, and 45 °C). Fermentation performance of the immobilized yeast on banana leaf sheath pieces and the free yeast were evaluated and compared. Generally, ethanol production of the immobilized and free yeast was stable in a temperature range of 30–40 °C. Temperature of 45 °C restricted yeast growth and lengthened the fermentation. The immobilized yeast demonstrated faster sugar assimilation and higher ethanol level in the fermentation broth in comparison with the free yeast at all fermentation temperatures. Change in fatty acid level in cellular membrane was determined to clarify the response of the free and immobilized yeast to thermal stress. The free cells of K. marxianus responded to temperature increase by increasing saturated fatty acid (C16:0 and C18:0) level and by decreasing unsaturated fatty acid (C18:1 and C18:2) level in cellular membrane. For fermentation at 40 °C with immobilized cells of K. marxianus, however, the changes were not observed in both saturated fatty acid (C16:0) and unsaturated fatty acid (C18:1 and C18:2) level.     

Effect of freeze-dried immobilized cells on delignified cellulosic material in low-temperature and ambient-temperature wine making

In this article, were port on wine making by freeze-dried immobilized cells on delignified cellulosic material for ambient and low temperatures. Biocatalyst supported by freeze-dried delignified cellulosic (FDC) material recovered after the first repeated-batch fermentations the fermentation efficiency and startup, which become about equal to those of biocatalyst supported by wet delignified cellulosic material. The FDC biocatalyst was suitable for wine making at low temperatures (5–15°C), and produced wine of 12% alcoholic degree, with the main volatiles contained in the wine and reduced by a decrease in temperature. The fermentation efficiency was not affected by total acidity of must, while an increase in initial Be density improved percentages of higher alcohols and ethylacetate. The quality of the wine was validated by a preliminary taste test to be in the range of acceptable to excellent.     

Alumina cryogels with superior thermal stability for catalyst supports

Alumina cryogels were synthesized from a colloidal boehmite sol through a sol–gel processing and subsequent freeze drying, and thermal stability was examined by comparison to that of the corresponding xerogel, precipitate and commercial alumina. N₂ adsorption, X-ray powder diffraction and transmittance electron micrography observations revealed that the stability was higher for the cryogel than for others in particular at temperatures above 1,000 °C. The higher stability was ascribed to the fine and uniform primary particles with fibrous shapes formed by the sol–gel technique and furthermore to the suppression of aggregation of the primary particles owing to the subsequent freeze drying. It was also found that aluminum sec-butoxide employed as a precursor for the preparation of boehmite sol was preferable compared to aluminum iso-propoxide.     

Catalytic activity and stability of laccase entrapped in sol–gel silica with additives

This study investigated the effects of different additives and precursors on the catalytic activity of laccase entrapped in sol–gel silica. It was found that the laccase catalytic activity and stability of sol–gel laccase could be enhanced if the entrapment was performed in the presence of additives such as PVA, PEG and APTS. The use of TEOS as a precursor showed slightly higher laccase catalytic activity compared to TMOS. The PVA as an additive showed a better catalytic activity enhancement compared to the PEG and APTMS with the optimum PVA concentration of 0.03 mg/mL. The optimal temperatures of sol–gel laccase without and with additives were found to be at 40 and 27°C, respectively. After 70 days of storage at 27°C, the catalytic activity of the immobilized sol–gel laccase with additives maintained its catalytic activity compared to only 30% of its original catalytic activity for the sol–gel laccase without additives.     

Thermal analysis of two types of dextran-coated magnetite

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C.     

Synthesis of high specific surface area YSZ (ZrO<Subscript>2</Subscript>–8Y<Subscript>2</Subscript>O<Subscript>3</Subscript>) nanocrystalline powder by modified polymerized complex method

In this study high specific surface area yttria-stabilized zirconia (ZrO₂–8Y₂O₃) nanocrystalline powder have been synthesized through “modified polymerized complex (MPC) method”. Zirconium chloride, yttrium nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel-like mass in which metallic ions were uniformly distributed. During the thermal treatment of dried gel, nanocrystalline YSZ powder was formed. Thermal reactions and phase formation of dried gel were investigated through thermal analysis (DTA/TG) and X-ray diffraction (XRD) analysis, respectively. Chemical bonding and thermal decomposition behavior of dried gel was investigated by FTIR analysis. During decomposition, the nature of the bonding between carboxylate groups and the cations changed from unidentate to bridging at 370 °C and carbonate species were detected at 470 °C. Morphology of powder calcined at 650 °C was analyzed by scanning electron microscope (SEM). YSZ powder with high specific surface area was prepared successfully by this method.     

Thermogravimetric investigation of the effect of annealing conditions on the soft ferrite phase homogeneity

In the present work, the conventional method of increasing the efficiency of solid-phase synthesis of lithium–zinc ferrites that involves multiple intermediate grinding of briquetted reaction mixtures annealed at high temperatures is compared with a new radiation-thermal (RT) method using a high-power pulsed beam of accelerated electrons for heating of reaction mixtures. An analysis of the TG(M)/DTG(M) curves recorded in a magnetic field demonstrates that the efficiency of Li_0.3Zn_0.4Fe_2.3O₄ synthesis from Li₂CO₃–Fe₂O₃–ZnO mechanical mixture at a temperature of 700 °C during 120 min is equivalent to thermal annealing at 800 °C, but with the triple annealing duration.     

Formation of functional phosphosilicate gels from phytic acid and tetraethyl orthosilicate

Phosphosilicate gels with high phosphorus content (P mol% > Si mol%) have been prepared using phytic acid as the phosphorus precursor, with tetraethyl orthosilicate (TEOS). It is shown that the structure of phytic acid is maintained in both the sols and those gels dried at a low temperature (i.e. ≤120 °C). Solid state ²⁹Si and ³¹P NMR suggest that the gel network is primarily based on tetrahedral silicon and that phosphorus is not chemically incorporated into the silicate network at this point. X-ray diffraction shows the gel to be amorphous at low temperatures. After heat treatment at higher temperatures (i.e. up to 450 °C), P–O–Si linkages are formed and the silicon coordination changes from tetrahedral to octahedral. At the same time, the gel crystallizes. Even after this partial calcination, ³¹P NMR shows that a large fraction of phytic acid remains in the network. The function of phytic acid as chelating agent is also maintained in the gels dried at 120 °C such that its ability to absorb Ca²⁺ from aqueous solution is preserved.     

Thermal characterization of starch-based polymers produced by <Emphasis Type="Italic">Ophiostoma</Emphasis> spp

The thermal behavior of modified starches (MS) produced by biosynthetic pathway is described based on a comparative analysis with native starches (NS). MS were produced by fermentation in presence of Ophiostoma spp. cultures. Thermogravimetric analysis (TG) with successive derivatives (DTG) and differential scanning calorimetry (DSC) were used for this study. NS results showed a single peak dominating both the TG (DTG) and DSC plots. A double thermal transition event was detected in samples of MS. The procedural decomposition temperature (T _i–T _f; lowest onset temperature of initial and final mass change) was carried out within a narrow interval of temperatures for NS (610–640 °C). This interval could not be reached within the 1,000 °C range in MS. Residues higher than 10% were recorded for MS at this temperature. The presence of the double thermal transition in MS is discussed.     

Polyurea based aerogel for a high performance thermal insulation material

Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications and as a thermal insulation component of spacesuits.     

PlyC,an enzyme lysing group A,C, and E streptococci: Specific features of inactivation and the stabilization by intramolecular chemical crosslinking

The heat inactivation kinetics of PlyC lysin, an enzyme that lyses groups A, C, and E streptococcal cells, has been studied. It has been demonstrated that oligomeric PlyC is inactivated according to a dissociative mechanism in the temperature range of 37–41.5°C, pH 6–8, and enzyme concentrations of 0.3–160 μg/ml and at higher (42–50°C) or lower (35–22°C) temperatures, according to a monomolecular mechanism. A new efficient method for PlyC stabilization via intramolecular chemical crosslinking was proposed.     

Comparison of catalytic properties of free and immobilized cellobiase Novozym 188

The enzyme cellobiase from Novo was immobilized in controlled pore silica particles by covalent binding with the silane-glutaraldehyde method with protein and activity yields of 67 and 13.7%, respectively. The activity of the free enzyme (FE) and immobilized enzyme (IE) was determined with 2 g/L of cellobiose, from 40 to 75°C at pH 3.0–7.0 for FE and from 40 to 70°C at pH 2.2–7.0 for IE. At pH 4.8 the maximum specific activity for the FE and IE occurred at 65°C: 17.8 and 2.2 micromol of glucose/(min·mg of protein), respectively. For all temperatures the optimum pH observed for FE was 4.5 whereas for IE it was shifted to 3.5. The energy of activation was 11 kcal/mol for FE and 5 kcal/mol for IE at pH 4.5–5, showing apparent diffusional limitation for the latter. Thermal stability of the FE and IE was determined with 2 g/L of cellobiose (pH 4.8) at temperatures from 40 to 70°C for FE and 40 to 75°C for IE. Free cellobiase maintained its activity practically constant for 240 min at temperatures up to 55°C. The IE has shown higher stability, retaining its activity in the sametest up to 60°C. Half-life experimental results for FE were 14.1, 2.1, and 0.17 h at 60, 65, and 70°C, respectively, whereas IE at the same temperatures had half-lives of 245, 21.3, and 2.9 h. The energy of thermal deactivation was 80.6 k cal/mol for the free enzyme and 85.2 k cal/mol for the IE, suggesting stabilization by immobilization.