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1.
The effects of chemical and enzymatic interesterification on the structure and rheological behavior of blends of fully hydrogenated
canola oil (FHCO) with high oleic acid sunflower oil in the range of 10–90% was studied. Relationships between chemical composition,
crystallization temperature (20–50°C), solid fat content (SFC) of the blends, and their rheological properties, characterized
using both small and large deformation mechanical testing, were investigated. The storage modulus (G′) and yield force increased with FHCO concentration in the blends and was affected strongly by interesterification. The SFC
in the interesterified samples was lower than in the non-interesterified blends, but they had higher values of G′. This increase in G′ at 30°C upon interesterification was attributed to a decrease in the fractal dimension of the fat crystal network which
translates into a decrease in crystal cluster size in the interesterified samples. The higher G′ in the chemically interesterified samples relative to the enzymatic interesterified samples, on the other hand, was due
to a higher λ parameter which is directly proportional to the strength of interparticle interactions and inversely proportional to crystal
size. Microscopy and nucleation kinetics studies allowed for the independent determination of λ. 相似文献
2.
Ana Paula Badan Ribeiro Renato Grimaldi Luiz Antonio Gioielli Adenilson Oliveira dos Santos Lisandro Pavie Cardoso Lireny A. Guaraldo Gonçalves 《Food biophysics》2009,4(2):106-118
Blends of soybean oil (SO) and fully hydrogenated soybean oil (FHSBO), with 10, 20, 30, 40, and 50% (w/w) FHSBO content were interesterified under the following conditions: 20 min reaction time, 0.4% sodium methoxide catalyst,
and 500 rpm stirring speed, at 100 °C. The original and interesterified blends were examined for triacylglycerol composition,
thermal behavior, microstructure, crystallization kinetics, and polymorphism. Interesterification produced substantial rearrangement
of the triacylglycerol species in all the blends, reduction of trisaturated triacylglycerol content and increase in monounsaturated–disaturated
and diunsaturated–monosaturated triacylglycerols. Evaluation of thermal behavior parameters showed linear relations with FHSBO
content in the original blends. Blend melting and crystallization thermograms were significantly modified by the randomization.
Interesterification caused significant reductions in maximum crystal diameter in all blends, in addition to modifying crystal
morphology. Characterization of crystallization kinetics revealed that crystal formation induction period (τ
SFC) and maximum solid fat content (SFCmáx) were altered according to FHSBO content in the original blends and as a result of the random rearrangement. Changes in Avrami
constant (k) and exponent (n) indicated, respectively, that—as compared with the original blends—interesterification decreased crystallization velocities
and modified crystallization processes, altering crystalline morphology and nucleation mechanism. X-ray diffraction analyses
revealed that interesterification altered crystalline polymorphism. The interesterified blends showed a predominance of the
β′ polymorph, which is of more interest for food applications. 相似文献
3.
Two 60-day experiments were conducted to study the influence of photon flux density (PFD) and temperature on the attachment
and development of Gloiopeltis tenax and Gloiopeltis furcata tetraspores. In the first experiment, tetraspores of the two Gloiopeltis species were incubated at five temperature ranges (8°C, 12°C, 16°C, 20°C, 24°C) under a constant PFD of 80 μmol photons m−2 s−1 with a photoperiod of 12:12. In a second experiment, tetraspores were incubated under five PFD gradients (30, 55, 80, 105,
130 μmol photons m−2 s−1) at a constant temperature of 16°C with a photoperiod of 12:12. Maximum density of attached tetraspores was observed at 16°C
for both species. Maximum per cent of spore germinating into disc was recorded at 12–16°C for G. tenax and 8–12°C for G. furcata. Maximum per cent of discs producing erect axes for G. tenax and G. furcata were recorded at 24°C and 20°C, respectively. Light had no significant effect on tetraspore attachment and developing into
disc, but it affected the growth, sprouting and survival of its discs. Under 30–55 μmol photons m−2 s−1, the discs of the two species of Gloiopeltis did not form thallus until the end of the experiment. Optimum PFD range for G. tenax discs was 80–105 μmol photons m−2 s−1, whilst it was 80–130 μmol photons m−2 s−1 for G. furcata. Results presented in this study are expected to assist the progress of artificial seeding of Gloiopeltis. 相似文献
4.
A variety of autotrophic, sulfur- and hydrogen-oxidizing thermophilic bacteria were isolated from thermogenic composts at
temperatures of 60–80° C. All were penicillin G sensitive, which proves that they belong to the Bacteria domain. The obligately
autotrophic, non-spore-forming strains were gram-negative rods growing at 60–80°C, with an optimum at 70–75°C, but only under
microaerophilic conditions (5 kPa oxygen). These strains had similar DNA G+C content (34.7–37.6 mol%) and showed a high DNA:DNA
homology (70–87%) with Hydrogenobacter strains isolated from geothermal areas. The facultatively autotrophic strains isolated from hot composts were gram-variable
rods that formed spherical and terminal endospores, except for one strain. The strains grew at 55–75° C, with an optimum at
65–70° C. These bacteria were able to grow heterotrophically, or autotrophically with hydrogen; however, they oxidized thiosulfate
under mixotrophic growth conditions (e.g. pyruvate or hydrogen plus thiosulfate). These strains had similar DNA G+C content
(60–64 mol%) to and high DNA:DNA homology (> 75%) with the reference strain of Bacillus schlegelii. This is the first report of thermogenic composts as habitats of thermophilic sulfur- and hydrogen-oxidizing bacteria, which
to date have been known only from geothermal manifestations. This contrasts with the generally held belief that thermogenic
composts at temperatures above 60° C support only a very low diversity of obligatory heterotrophic thermophiles related to
Bacillus stearothermophilus.
Received: 20 July 1995 / Accepted: 25 September 1995 相似文献
5.
Xyloglucanase from an extracellular culture filtrate of alkalothermophilic Thermomonospora sp. was purified to homogeneity with a molecular weight of 144 kDa as determined by SDS-PAGE and exhibited specificity towards
xyloglucan with apparent K
m of 1.67 mg/ml. The enzyme was active at a broad range of pH (5–8) and temperatures (40–80°C). The optimum pH and temperature
were 7 and 70°C, respectively. The enzyme retained 100% activity at 50°C for 60 h with half-lives of 14 h, 6 h and 7 min at
60, 70 and 80°C, respectively. The kinetics of thermal denaturation revealed that the inactivation at 80°C is due to unfolding
of the enzyme as evidenced by the distinct red shift in the wavelength maximum of the fluorescence profile. Xyloglucanase
activity was positively modulated in the presence of Zn2+, K+, cysteine, β-mercaptoethanol and polyols. Thermostability was enhanced in the presence of additives (polyols and glycine)
at 80°C. A hydrolysis of 55% for galactoxyloglucan (GXG) from tamarind kernel powder (TKP) was obtained in 12 h at 60°C and
6 h at 70°C using thermostable xyloglucanases, favouring a reduction in process time and enzyme dosage. The enzyme was stable
in the presence of commercial detergents (Ariel), indicating its potential as an additive to laundry detergents. 相似文献
6.
Identification and characterization of fermentation inhibitors formed during hydrothermal treatment and following SSF of wheat straw 总被引:1,自引:0,他引:1
Mette Hedegaard Thomsen Anders Thygesen Anne Belinda Thomsen 《Applied microbiology and biotechnology》2009,83(3):447-455
A pilot plant for hydrothermal treatment of wheat straw was compared in reactor systems of two steps (first, 80°C; second,
190–205°C) and of three steps (first, 80°C; second, 170–180°C; third, 195°C). Fermentation (SSF) with Sacharomyces cerevisiae of the pretreated fibers and hydrolysate from the two-step system gave higher ethanol yield (64–75%) than that obtained from
the three-step system (61–65%), due to higher enzymatic cellulose convertibility. At the optimal conditions (two steps, 195°C
for 6 min), 69% of available C6-sugar could be fermented into ethanol with a high hemicellulose recovery (65%). The concentration
of furfural obtained during the pretreatment process increased versus temperature from 50 mg/l at 190°C to 1,200 mg/l at 205°C
as a result of xylose degradation. S. cerevisiae detoxified the hydrolysates by degradation of several toxic compounds such as 90–99% furfural and 80–100% phenolic aldehydes,
which extended the lag phase to 5 h. Acetic acid concentration increased by 0.2–1 g/l during enzymatic hydrolysis and 0–3.4 g/l
during fermentation due to hydrolysis of acetyl groups and minor xylose degradation. Formic acid concentration increased by
0.5–1.5 g/l probably due to degradation of furfural. Phenolic aldehydes were oxidized to the corresponding acids during fermentation
reducing the inhibition level. 相似文献
7.
Palm stearin (PS) and rice bran oil (RBO) blends of varying proportions were subjected to enzymatic interesterification (EIE) using a 1,3 specific immobilized lipase. The interesterified blends were evaluated for their physicochemical characteristics and bioactive phytochemical contents using differential scanning calorimeter (DSC), X-ray diffraction (XRD), gas chromatography (GC) and high performance liquid chromatography (HPLC). The blends of PS and RBO in different proportions (40:60, 50:50, 60:40 and 70:30) had saturated fatty acid content and unsaturated fatty acid content in the range of 37.6-52.0% and 48.0-62.4%, respectively. The blends 40:60, 50:50 and 60:40 showed a considerable reduction in their highest melt peak temperature (TP) and solid fat content (SFC) on EIE. The interesterified blends retained bioactive phytochemicals like tocols (839-1172 ppm), sterols (4318-9647 ppm), oryzanols (3000-6800ppm) and carotene (121-180 ppm). XRD studies demonstrated that the interesterified blends contained beta and beta' polymorphic forms. 相似文献
8.
Martín Núñez Aleida J. Sandoval Alejandro J. Müller Guy Della Valle Denis Lourdin 《Food biophysics》2009,4(4):291-303
Gelatinization in excess of water and melting transition for different moisture contents of a ready-to-eat cereal formulation
(RTE blend) and its major components, (i.e., oat flour, rice flour, and an oat–rice flour blend) were studied by differential
scanning calorimetry (DSC) and rapid visco-analyzer (RVA). The highest swelling power was exhibited by the rice flour and
the lowest by the RTE blend. Two endothermic peaks under excess of water were exhibited by all materials, at 53–75 °C and
80–102 °C, and they were associated to gelatinization and cereal protein denaturation, respectively. A third peak appearing
in all materials except in rice flour, at higher temperatures (102–116 °C), was attributed to the melting of the amylose–lipid
complexes. The effect of water in the melting of the flours and blends was well described by the Flory–Huggins equation and
its parameters agreed well with those reported in the literature for starchy products. A theoretical value of the polymer–diluent
(starch–water) interaction factor for starch of 0.36 was calculated from a combined model of Hildebrand empirical approach
to solubility and the Flory–Huggins theory, and reasonably compared with the interaction parameter (χ) obtained for the materials considered in this work. State diagrams for the oat–rice flour blend and for the RTE blend going
through an extrusion process were finally obtained. 相似文献
9.
R. Oelkrug G. Heldmaier C. W. Meyer 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(1):137-145
In eutherian mammals, uncoupling protein 1 (UCP1) mediated non-shivering thermogenesis from brown adipose tissue (BAT) provides
a mechanism through which arousal from torpor and hibernation is facilitated. In order to directly assess the magnitude by
which the presence or absence of UCP1 affects torpor patterns, rewarming and arousal rates within one species we compared
fasting induced torpor in wildtype (UCP1+/+) and UCP1-ablated mice (UCP−/−). Torpor was induced by depriving mice of food for up to 48 h and by a reduction of ambient temperature (T
a) from 30 to 18°C at four different time points after 18, 24, 30 and 36 h of food deprivation. In most cases, torpor bouts
occurred within 20 min after the switch in ambient temperature (30–18°C). Torpor bouts expressed during the light phase lasted
3–6 h while significantly longer bouts (up to 16 h) were observed when mice entered torpor during the dark phase. The degree
of hypometabolism (5–22 ml h−1) and hypothermia (19.5–26.7°C) was comparable in wildtype and UCP1-ablated mice, and both genotypes were able to regain normothermia.
In contrast to wildtype mice, UCP1-ablated mice did not display multiple torpor bouts per day and their peak rewarming rates
from torpor were reduced by 50% (UCP1+/+: 0.24 ± 0.08°C min−1; UCP1−/−: 0.12 ± 0.04°C min−1). UCP1-ablated mice therefore took significantly longer to rewarm from 25 to 32°C (39 vs. 70 min) and required 60% more energy
for this process. Our results demonstrate the energetic benefit of functional BAT for rapid arousal from torpor. They also
suggest that torpor entry and maintenance may be dependent on endogenous rhythms. 相似文献
10.
Vikramathithan J Muthuraman P Ravikumar S Shayamala S Kumar GN Srikumar K 《The protein journal》2012,31(2):141-149
Two thermostable xylanase isoforms T60 and T80 were purified to homogeneity from the cladodes of the xerophytic Cereus pterogonus plant species. After three consecutive purification steps, the specific activity of T60 and T80 isoforms were found to be 178.6 and 216.2 U mg−1 respectively. The molecular mass of both isoforms was determined to be 80 kDa. The optimum temperature for T60 and T80 xylanase isoforms were 60 and 80 °C respectively. The pH was 5.0 for both isoforms. The presence of divalent metal ions (10 mM
Co2+) showed stimulatory effects of both catalytic activities, where as in the presence of Hg2+, Cd2+, Cu2+ showed inhibitory effect on these activities at all concentrations studied. The thermodynamic analysis of xylanase activity
using denaturation kinetics and the presence divalent cations at 30–100 °C, showed lower ΔH, ΔS, and ΔG values at all the temperatures investigated. The melting temperature of purified T80 xylanase isoform as determined by TG/DTA analysis and it showed the unfolding temperature was 80 °C. The g value and hyperfine
(A) value purified xylanase T80 isoform was 2.017 and 10.80 respectively. Immunoblot analysis with antiserum raised against the purified T80 xylanase isoforms revealed single immunolgically related polypeptides of 80 kDa, identical with the polypeptide band produced
on SDS-PAGE. The results of double immunodiffusion against the T80 isoforms showed a single precipitin line indicating that the serum used was specific to these xylanase isoforms. The kinetic
and thermodynamic properties suggested that xylanase from C. pterogonus may have a potential usage in various industries. 相似文献
11.
Lipase-catalyzed synthesis of isoamyl acetate in hexane at 10–250 MPa at 80°C and 1–100 MPa at 40°C resulted in activation
volumes of −12.9 ± 1.7 and −21.6 ± 2.9 cm3 mol−1, respectively. Increasing pressure from 10 to 200 MPa resulted in approximately 10-fold increase in V
max at both 40 and 80°C. Pressure increased the K
m from 2.4 ± 0.004 to 38 ± 0.78 mM at 40°C. In contrast, at 80°C the pressure did not affect the K
m. 相似文献
12.
The composition of the most abundant facultative anaerobic bacteria populations [faecal coliforms (FC) and enterococci (ENT)]
in sludge can be modified after different treatments. These involve the disposal or reuse of sludge and include: anaerobic
digesters, incineration, composting, pasteurization and lime treatments. In this study, three treatment types (mesophilic
anaerobic digestion, composting and pasteurization) were compared in terms of their ability to reduce both bacterial populations.
The diversity and any changes in composition of main phenotypic groups for both populations were also analyzed. Mesophilic
anaerobic digestion (MAD) was carried out at 35°C for 20 days. Digested sludge was then dehydrated by centrifugation at 2,500 rpm.
Composting (COM) was performed at 55°C with windrow phases. Pasteurization was assayed at 60°C for 90 min (P60), at 80°C for
60 min (P80). A 1–1.5 log unit reduction was observed for FC, and 1 log unit reduction was noted for ENT by MAD treatment.
In composting, this reduction proved higher for FC than for ENT (6 log and 3–4 log units, respectively). Optimal pasteurization
was obtained at 80°C for 60 min, resulting in a 5 log unit reduction for FC and a 2 log unit reduction for ENT. High diversity
indices (Di) for both bacterial populations were detected both before and after implementation of the different treatments. Analyses
of the population’s similarity provided that FC were diverse both before and after COM, P60 and P80 treatments. However, no
differences were observed on the composition of ENT populations after the different treatments assayed. 相似文献
13.
Huiying Luo Jiang Li Jun Yang Hui Wang Yuhui Yang Huoqing Huang Pengjun Shi Tiezheng Yuan Yunliu Fan Bin Yao 《Extremophiles : life under extreme conditions》2009,13(5):849-857
A complete gene, xyl10C, encoding a thermophilic endo-1,4-β-xylanase (XYL10C), was cloned from the acidophilic fungus Bispora sp. MEY-1 and expressed in Pichia pastoris. XYL10C shares highest nucleotide and amino acid sequence identities of 57.3 and 49.7%, respectively, with a putative xylanase
from Aspergillus fumigatus Af293 of glycoside hydrolase family 10. A high expression level in P. pastoris (73,400 U ml−1) was achieved in a 3.7–l fermenter. The purified recombinant XYL10C was thermophilic, exhibiting maximum activity at 85°C,
which is higher than that reported from any fungal xylanase. The enzyme was also highly thermostable, exhibiting ~100% of
the initial activity after incubation at 80°C for 60 min and >87% of activity at 90°C for 10 min. The half lives of XYL10C
at 80 and 85°C were approximately 45 and 3 h, respectively. It had two activity peaks at pH 3.0 and 4.5–5.0 (maximum), respectively,
and was very acid stable, retaining more than 80% activity after incubation at pH 1.5−6.0 for 1 h. The enzyme was resistant
to Co2+, Mn2+, Cr3+ and Ag+. The specific activity of XYL10C for oat spelt xylan was 18,831 U mg−1. It also had wide substrate specificity and produced simple products (65.1% xylose, 25.0% xylobiose and 9.9% xylan polymer)
from oat spelt xylan. 相似文献
14.
Thermophilic enzymes are in high demand for various applications due to their prolonged lifetimes and high reaction rates
at elevated temperatures. In this work, an open reading frame TM0295, which encodes a putative transaldolase (TAL) from a
hyper-thermophilic microorganism, Thermotoga maritima, was cloned and expressed in Escherichia coli. The enzyme activity of transaldolase at high temperatures (e.g., at 80 °C) was reported here for the first time. The recombinant
T. maritima transaldolase was extremely thermostable, with a half-life time of 198 and 13.0 h at 60 °C and 80 °C, respectively. The estimated
total turn-over number was 1.5 × 106 mol of product per mol of enzyme at 80 °C. This enzyme also exhibited high activities within a broad pH range of 6.0–9.0.
This ultra-thermostable TAL with high activity shows great potential for use in such applications as the production of enzymatic
biofuels production and the synthesis of high-value carbohydrates by cell-free synthetic pathway biotransformation. 相似文献
15.
Han Gil Choi Ki Hoon Lee Hyun Il Yoo Pil Jun Kang Young Sik Kim Ki Wan Nam 《Journal of applied phycology》2008,20(5):729-735
The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance
(10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m−2s−1) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m−2s−1), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day−1 (25°C, 20 μmol photons m−2s−1) and 13% day−1 (8 h daylength). In contrast, the RGRs of the blade weights were 4% day−1 (15°C, 20 μmol photons m−2s−1) and 5% day−1 (12 h daylength). Negative growth rates were found at 20 μmol photons m−2s−1 of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m−2s−1, and 8 h daylength for construction of Sargassum beds and restoration of barren areas. 相似文献
16.
Melike Balk Hans G. H. J. Heilig Miriam H. A. van Eekert Alfons J. M. Stams Irene C. Rijpstra Jaap S. Sinninghe-Damsté Willem M. de Vos Servé W. M. Kengen 《Extremophiles : life under extreme conditions》2009,13(6):885-894
A novel anaerobic, thermophilic, Gram-positive, spore-forming, and sugar-fermenting bacterium (strain TLO) was isolated from
a geothermal spring in Ayaş, Turkey. The cells were straight to curved rods, 0.4–0.6 μm in diameter and 3.5–10 μm in length.
Spores were terminal and round. The temperature range for growth was 40–80°C, with an optimum at 70°C. The pH optimum was
between 6.3 and 6.8. Strain TLO has the capability to ferment a wide variety of mono-, di-, and polysaccharides and proteinaceous
substrates, producing mainly lactate, next to acetate, ethanol, alanine, H2, and CO2. Remarkably, the bacterium was able to grow in an atmosphere of up to 25% of CO as sole electron donor. CO oxidation was
coupled to H2 and CO2 formation. The G + C content of the genomic DNA was 35.1 mol%. Based on 16S rRNA gene sequence analysis and the DNA–DNA hybridization
data, this bacterium is most closely related to Thermoanaerobacter thermohydrosulfuricus and Thermoanaerobacter siderophilus (99% similarity for both). However, strain TLO differs from Thermoanaerobacter thermohydrosulfuricus in important aspects, such as CO-utilization and lipid composition. These differences led us to propose that strain TLO represents
a subspecies of Thermoanaerobacter thermohydrosulfuricus, and we therefore name it Thermoanaerobacter thermohydrosulfuricus subsp. carboxydovorans. 相似文献
17.
M. Michelin S. C. Peixoto-Nogueira J. H. A. Betini T. M. da Silva J. A. Jorge H. F. Terenzi M. L. T. M. Polizeli 《Bioprocess and biosystems engineering》2010,33(7):813-821
Aspergillus terricola and Aspergillus ochraceus, isolated from Brazilian soil, were cultivated in Vogel and Adams media supplemented with 20 different carbon sources, at
30 °C, under static conditions, for 120 and 144 h, respectively. High levels of cellulase-free xylanase were produced in birchwood
or oat spelt xylan-media. Wheat bran was the most favorable agricultural residue for xylanase production. Maximum activity
was obtained at 60 °C and pH 6.5 for A. terricola, and 65 °C and pH 5.0 for A. ochraceus. A. terricola xylanase was stable for 1 h at 60 °C and retained 50% activity after 80 min, while A. ochraceus xylanase presented a t
50 of 10 min. The xylanases were stable in an alkali pH range. Biobleaching of 10 U/g dry cellulose pulp resulted in 14.3% delignification
(A. terricola) and 36.4% (A. ochraceus). The brightness was 2.4–3.4% ISO higher than the control. Analysis in SEM showed defibrillation of the microfibrils. Arabinase
traces and β-xylosidase were detected which might act synergistically with xylanase. 相似文献
18.
A putative N-acyl-d-glucosamine 2-epimerase from Caldicellulosiruptor saccharolyticus was cloned and expressed in Escherichia coli. The recombinant enzyme was identified as a cellobiose 2-epimerase by the analysis of the activity for substrates, acid-hydrolyzed
products, and amino acid sequence. The cellobiose 2-epimerase was purified with a specific activity of 35 nmol min–1 mg–1 for d-glucose with a 47-kDa monomer. The epimerization activity for d-glucose was maximal at pH 7.5 and 75°C. The half-lives of the enzyme at 60°C, 65°C, 70°C, 75°C, and 80°C were 142, 71, 35,
18, and 4.6 h, respectively. The enzyme catalyzed the epimerization reactions of the aldoses harboring hydroxyl groups oriented
in the right-hand configuration at the C2 position and the left-hand configuration at the C3 position, such as d-glucose, d-xylose, l-altrose, l-idose, and l-arabinose, to their C2 epimers, such as d-mannose, d-lyxose, l-allose, l-gulose, and l-ribose, respectively. The enzyme catalyzed also the isomerization reactions. The enzyme exhibited the highest activity for
mannose among monosaccharides. Thus, mannose at 75 g l–1 and fructose at 47.5 g l–1 were produced from 500 g l–1 glucose at pH 7.5 and 75°C over 3 h by the enzyme. 相似文献
19.
A new xylanase from thermoacidophilic Alicyclobacillus sp. A4 with broad-range pH activity and pH stability 总被引:1,自引:0,他引:1
Yingguo Bai Jianshe Wang Zhifang Zhang Peilong Yang Pengjun Shi Huiying Luo Kun Meng Huoqing Huang Bin Yao 《Journal of industrial microbiology & biotechnology》2010,37(2):187-194
We have identified a highly pH-adaptable and stable xylanase (XynA4) from the thermoacidophilic Alicyclobacillus sp. A4, a strain that was isolated from a hot spring in Yunnan Province, China. The gene (xynA4) that encodes this xylanase was cloned, sequenced, and expressed in Escherichia coli. It encodes a 338-residue polypeptide with a calculated molecular mass of 42.5 kDa. The deduced amino acid sequence is most
similar to (53% identity) an endo-1,4-β-xylanase from Geobacillus stearothermophilus that belongs to family 10 of the glycoside hydrolases. Purified recombinant XynA4 exhibited maximum activity at 55°C and
pH 7.0, had broad pH adaptability (>40% activity at pH 3.8–9.4) and stability (retaining >80% activity after incubation at
pH 2.6–12.0 for 1 h at 37°C), and was highly thermostable (retaining >90% activity after incubation at 60°C for 1 h at pH
7.0). These properties make XynA4 promising for application in the paper industry. This is the first report that describes
cloning and expression of a xylanase gene from the genus Alicyclobacillus. 相似文献
20.
MA Giraldo TM da Silva F Salvato HF Terenzi JA Jorge LH Guimarães 《World journal of microbiology & biotechnology》2012,28(2):463-472
The filamentous fungus Paecylomices variotii was able to produce high levels of cell extract and extracellular invertases when grown under submerged fermentation (SbmF)
and solid-state fermentation, using agroindustrial products or residues as substrates, mainly soy bran and wheat bran, at
40°C for 72 h and 96 h, respectively. Addition of glucose or fructose (≥1%; w/v) in SbmF inhibited enzyme production, while
the addition of 1% (w/v) peptone as organic nitrogen source enhanced the production by 3.7-fold. However, 1% (w/v) (NH4)2HPO4 inhibited enzyme production around 80%. The extracellular form was purified until electrophoretic homogeneity (10.5-fold
with 33% recovery) by DEAE-Fractogel and Sephacryl S-200 chromatography. The enzyme is a monomer with molecular mass of 102 kDa
estimated by SDS–PAGE with carbohydrate content of 53.6%. Optima of temperature and pH for both, extracellular and cell extract
invertases, were 60°C and 4.0–4.5, respectively. Both invertases were stable for 1 h at 60°C with half-lives of 10 min at
70°C. Mg2+, Ba2+ and Mn2+ activated both extracellular and cell extract invertases from P. variotii. The kinetic parameters Km and Vmax for the purified extracellular enzyme corresponded to 2.5 mM and 481 U/mg prot−1, respectively. 相似文献