Application In Bleaching Research Articles

The Effect of Ultrasonic Waves in Bleaching of Olive and Sunflower Oils and Comparison with Conventional Bleaching

This study was aimed to bleach olive and sunflower oils by using conventional and ultrasonic methods. The qualitative and quantities characteristics of the bleached oils were compared. The used ultrasonic bath (150 W, 20 kHz) was set at two levels of temperatures (45 and 60C). Series of tests including of chlorophyll and carotenoid, color, peroxide value, acidity measurements and free fatty acid (FFA) determination were carried out. By application of conventional bleaching a considerable reduction in chlorophyll and carotenoid contents of olive and sunflower oils were observed, while better removal of the pigments was obtained after ultrasonic treatment for 20 and 30 min at 45 and 60C without any significant negative effect on the fatty acid composition. It might be concluded that the ultrasonic bleaching process can be considered as an alternative method for conventional bleaching method since it could decline the time and temperature of bleaching process. Practical Applications Technical information related to the possible effects of application of ultrasonic bleaching on some of quality parameters of olive and sunflower oils was provided by current study. Ultrasonic waves could improve the bleaching process without any destructive effect on the fatty acids profiles. The suggested method can be used in oil refining industry as alternative to current conventional producer due to reduction of the time and temperature of bleaching process.

AC electrokinetic drug delivery in dentistry using an interdigitated electrode assembly powered by inductive coupling.

AC electrokinetics (ACEK) has been shown to deliver certain drugs into human teeth more effectively than diffusion. However, using electrical wires to power intraoral ACEK devices poses risks to patients. The study demonstrates a novel interdigitated electrode arrays (IDE) assembly powered by inductive coupling to induce ACEK effects at appropriate frequencies to motivate drugs wirelessly. A signal generator produces the modulating signal, which multiplies with the carrier signal to produce the amplitude modulated (AM) signal. The AM signal goes through the inductive link to appear on the secondary coil, then rectified and filtered to dispose of its carrier signal, and the positive half of the modulating signal appears on the load. After characterizing the device, the device is validated under light microscopy by motivating carboxylate-modified microspheres, tetracycline, acetaminophen, benzocaine, lidocaine and carbamide peroxide particles with induced ACEK effects. The assembly is finally tested in a common dental bleaching application. After applying 35% carbamide peroxide to human teeth topically or with the IDE at 1200Hz, 5 Vpp for 20min, spectrophotometric analysis showed that compared to diffusion, the IDE enhanced whitening in specular optic and specular optic excluded modes by 215% and 194% respectively. Carbamide peroxide absorbance by the ACEK group was two times greater than diffusion as measured by colorimetric oxidation-reduction and UV-Vis spectroscopy at 550nm. The device motivates drugs of variable molecular weight and structure wirelessly. Wireless transport of drugs to intraoral targets under ACEK effects may potentially improve the efficacy and safety of drug delivery in dentistry.

Effect of different bleaching applications on the surface properties and staining susceptibility of dental composites

The aim of this study was to investigate the effects of two bleaching systems on micro hardness, surface roughness and color stability of two novel dental composites. Ormocer based restorative Admira and nano-filled composite Clearfil Majesty Esthetic were bleached with 10% carbamide peroxide (Opalescence PF) or 35% hydrogen peroxide (Beyond Max 5) and subsequently immersed in four different staining solutions (coffee, tea, red wine, and cola). Distilled water was used as a control. Color measurements were performed with a spectrophotometer. Vickers micro hardness and roughness data were analyzed with two-way analysis of variance for repeated measures. The analysis of variance was used to compare the color change values. Duncan’s multiple comparison test was applied to compare the results (α = 5%). ΔEab* values over 3.3 were considered clinically unacceptable. Micro hardness and surface roughness values of the tested composites were decreased significantly after bleaching applications. Red wine and tea storage caused perceptible discolorations in the composite resin materials after 30 days of 3-hour immersion. Home or office bleaching applications can affect the surface properties of resin composites and accelerate the staining process.

Surface decontamination for blister agents Lewisite, sulfur mustard and agent yellow, a Lewisite and sulfur mustard mixture

Sulfur mustard (HD) and Lewisite (L) are blister agents that have a high potential for terrorist use; Agent Yellow (HL) is the eutectic mixture of HD and L. Bench-scale testing was used to determine the residual amount of these chemical warfare agents remaining on three building materials (wood, metal and glass) after application of various decontaminants (household bleach, full strength and dilute; hydrogen peroxide 3% solution; and EasyDECON® DF200). All decontaminants reduced the amount of L recovered from coupons. Application of dilute bleach showed little or no difference compared to natural attenuation in the amount of HD recovered from coupons. Full-strength bleach was the most effective of four decontaminants at reducing the amount of HD from coupons. Hydrogen peroxide (3% solution) and DF200 did decrease the amount of HD recovered from coupons more than natural attenuation (except DF200 against HD on metal), but substantial amounts of HD remained on some materials. Toxic HD by-products were generated by hydrogen peroxide treatment. The effectiveness of decontaminants was found to depend on agent, material, and decontaminant. Increased decontaminant reaction time (60min rather than 30min) did not significantly increase effectiveness.

Effect of at-home bleaching with different thickeners and aging on physical properties of a nanocomposite.

Objective:To evaluate the influence of 16% carbamide peroxide (CP) containing different thickeners on the physical characteristics of a nanocomposite resin submitted or not to accelerated artificial aging (AAA).Materials and Methods:One hundred samples were randomly distributed into two groups (n = 50) according to AAA. Each group was divided into 5 subgroups (n = 10) depending on the bleaching/thickener treatment: CP + carbopol, CP + natrosol, carbopol, natrosol, and no treatment (control). The physical properties tested were color (ΔE), gloss (GU), mean roughness (Ra), and Knoop microhardness (KHN). The resin surface was performed with atomic force microscopy (AFM).Statistical Analysis:The color (variable Δ E) was assessed with two-way analysis of variance (ANOVA) and additionally with Tukey's and Dunnett's tests, the roughness values were submitted to Kruskal–Wallis, Dunn's, and Mann–Whitney's tests. Data on gloss and KHN were submitted to two-way ANOVA and Tukey's test (α = 0.05).Results:Among the physical properties evaluated, CP + carbopol promoted a reduction in composite microhardness only, thus differing statistically from the controls. As for CP + natrosol, such a change was not observed. The aging process reduced all the physical properties, thus differing statistically from the nonaging group. CP + carbopol increased the roughness and decreased the gloss of aged resins, whereas natrosol reduced gloss only, which differed statistically from the controls.Conclusions:AFM showed evidence of the loss of organic matrix and exposure to load particles in the aged samples. Therefore, the replacement of carbopol with natrosol provided maintenance of the composite microhardness following bleaching. The aging process reduced the physical properties evaluated, and some changes were enhanced by the application of bleaching.

An investigation of optical properties of zinc oxide nanoparticle synthesized by starch mediated assembly and its application in photocatalytic bleaching of methyl green and rhodamine-B

The self-assembled nanostructure has wide applications in the development of nanosensor and photocell. Here, we synthesized zinc oxide nanoparticle (ZnONP) by sodium hydroxide (NaOH) mediated reduction of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) using starch as a capping as well as assembly agent. The effect of various precursor concentration, and reaction temperature on the size and shape was analyzed. ZnONP was characterized by UV spectroscopy, dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), photolumiscence (PL), as well as thermogravimetric analysis (TGA). In addition, the effect of starch on PL was also evaluated. The results revealed that the use of increasing concentration of Zn(NO3)2·6H2O resulted in the increase of ZnONP size, but increasing starch concentration and calcination temperature showed reverse effect. Band gap analysis of ZnONP showed that band gap energy was increased with decreasing size of the nanoparticle (NP). PL analysis showed that ZnONP has excellent absorption in UV region and emission at 380nm Furthermore, the photocatalytic activity of ZnONP for Methyl green and Rhodamine-B were also investigated. The results revealed that incubation of dyes with ZnONP at a wavelength of 254nm ultraviolet spectra-C (UV-C) caused bleaching of both dyes and a gradual decrease in the absorption peak. Therefore, the analysis demonstrated that starch capped self-assembled ZnONP have potential use in nanosensor, as UV protectant and in the photocatalytic degradation of the harmful dye.

Effect of Bleaching Treatment on Fatigue Resistance and Flexural Strength of Bovine Dentin.

To determine the effects of bleach on dentin fatigue resistance and flexural strength. Eighty bovine dentin specimens (2 × 2 × 17 mm) were treated with: placebo or 10% carbamide peroxide bleach. Treatment was applied for 6 hours/day for 2 or 8 weeks. After treatment, 10 specimens per group were subjected to fatigue testing (10(6) cycles) whereas the other 10 were stored in artificial saliva as fatigue controls. The specimens undergoing fatigue were checked daily for visible signs of fracture and excluded from subsequent flexural strength tests if fractured. Fatigue control and surviving fatigued specimens were subjected to flexural strength testing. Chi-square, Kruskal-Wallis, factorial analysis of variance (p < 0.05) and Mann-Whitney (p < 0.002) tests were performed. There were significant differences in fatigue resistance (p = 0.003) and flexural strength rank scores (p < 0.0001) among the groups. None of the specimens in the "8-week bleach" group survived the fatigue testing. Fatigue (p = 0.005) and interaction of time and treatment (p = 0.039) were significant factors in the flexural strength results. Fatigued specimens had lower flexural strength than nonfatigued and "8-week bleach" had lower flexural strength than placebo and "2-week bleach" groups. Prolonged direct bleaching of bovine dentin reduces its fatigue resistance and flexural strength in vitro. Further research is needed in this area. It remains prudent to advise patients to limit their exposure to tooth bleaching materials by avoiding direct application of bleach to exposed dentin and by minimizing the duration of bleach treatment.

Cleaning-induced arsenic mobilization and chromium oxidation from CCA-wood deck: Potential risk to children

Concern about children's exposure to arsenic (As) from wood treated with chromated-copper-arsenate (CCA) led to its withdrawal from residential use in 2004. However, due to its effectiveness, millions of American homes still have CCA-wood decks on which children play. This study evaluated the effects of three deck-cleaning methods on formation of dislodgeable As and hexavalent chromium (CrVI) on CCA-wood surfaces and in leachate. Initial wipes from CCA-wood wetted with water showed 3–4 times more dislodgeable As than on dry wood. After cleaning with a bleach solution, 9.8–40.3μg/100cm2 of CrVI was found on the wood surface, with up to 170μg/L CrVI in the leachate. Depending on the cleaning method, 699–2473mg of As would be released into the environment from cleaning a 18.6-m2-deck. Estimated As doses in children aged 1–6 after 1h of playing on a wet CCA-wood deck were 0.25–0.41μg/kg. This is the first study to identify increased dislodgeable As on wet CCA-wood and to evaluate dislodgeable CrVI after bleach application. Our data suggest that As and CrVI in 25-year old CCA-wood still show exposure risks for children and potential for soil contamination.

Production of an alkaline xylanase from recombinant Kluyveromyces lactis (KY1) by submerged fermentation and its application in bio-bleaching

The aim of this work was to study the production of recombinant xylanase using a Kluyveromyces lactis GG799 strain with a plasmid vector pKLAC1 carrying xylanase coding gene (XynA) isolated from Bacillus pumilus MTCC 5015. To obtain maximum xylanase expression, statistical approaches based on response surface methodology (RSM) was employed. Critical variables for recombinant xylanase production were identified by one-variable-at- a- time approach followed by response surface methodology (RSM), which led to an enhancement in extracellular xylanase production (200IU/mL). Maximum xylanase production was obtained when 2% of casamino acid was used along with 5% of galactose (inducer) with an inoculum size of 2.75% (5×108 CFU/mL) when incubated for 48h with a pre-inoculum age of 24h (273IU/mL). Thus, a four-fold increase in activity from 70IU/mL to 273IU/mL could be achieved. SDS-PAGE analysis showed that the relative molecular mass of glycosylated XynA was about 35.0kDa. The partially purified enzyme was used for the bio-bleaching of paper carton, which showed its effective application in bleaching.

Effect of In-Office Bleaching Application on the Color, Microhardness and Surface Roughness of Five Esthetic Restorative Materials

The purpose of this in vitro study was to compare the effect of in-office bleaching application on the color, microhardness, and surface roughness of five different tooth-colored restorative materials. Thirty specimens were fabricated from each restorative materials nano-hybrid composite (Grandio/Voco), micro-hybrid composite (Filtek Z250/3M), flow able composite (Filtek P60/3M), compomer (Dyract AP/DentsplyDeTrey) and glass-ionomer cement (Ketac Molar Easymix/3M)] and divided into 3 subgroups. Specimens in group 1 were stored in distilled water at 37oC (control) during the hiatus period. Specimens in group 2 and 3 were treated with 15% hydrogen peroxide (HP) and 25% hydrogen peroxide, respectively. The data were analyzed with ANOVA and T-test. 15% HP and 25% HP groups showed an apparent color change (ΔE*) than control group. In particular, Dyract AP and Ketac Molar Easymix showed a noticeable color change and statistically significant differences (p 0.05), Dyract AP and Ketac Molar Easy mix showed a statistically significant difference (p<0.05). Surface roughness was increased in 25% HP group after bleaching. In-office bleaching agents may affect the surface of existing restorations. Bleaching agents should not be used indiscriminately when these restorations are present.

Spectrophotometric and computerized evaluation of tooth bleaching employing 10 different home-bleaching procedures: In-vitro study.

Objective:The aim of this in-vitro study was to evaluate the efficacy of bleaching products, determine the applicability and validation of the measurement methods.Materials and Methods:Freshly extracted 110 human incisor teeth were stained with whole blood and hemolysate solution prior to the application of 10 different home-bleaching products. Spectrophotometric measurements of the tooth shades were performed for each specimen before and after bleaching at the 1st, 3rd, 7th, and 14 days. Differences in lightness (Δl), chroma (Δc), hue (Δh) values and shade changes were measured to evaluate process. Computerized digital imaging analyses to determine the color changes were performed with Photoshop CS4 software (Adobe, San Jose, CA, USA). Statistical analyses were performed with analysis of variance, Scheffe and Tukey tests.Results:In all of the test groups regardless of the material used, a significant increase in lightness and hue, and decrease of chroma were observed, as compared to the control group. After recommended bleaching applications, Δl and Δh values respectively increased in group Zaris White and Brite (ZWB) and group Pola Night and Δc values showed significant decrease in groups ZWB and Rembrandt REM3 (P < 0.05). At the end of the procedure both spectrophotometric and digital imaging analysis showed ZWB was the most effective product among the others while Yotuel and Happy Smile were the least (P < 0.05).Conclusions:Home-bleaching systems showed slower but almost permanent bleaching effect likewise office-based methods. Both software and spectrophotometric analyses have advantages such as evaluating the results objectively and numerically, also treatment outcomes could be preserved.

Effect of inoculation method on the determination of decontamination efficacy against Bacillus spores.

Decontamination studies investigating the effectiveness of products and processes for the inactivation of Bacillus species spores have traditionally utilized metering viable spores in a liquid suspension onto test materials (coupons). The current study addresses the representativeness of studies using this type of inoculation method compared to when coupons are dosed with a metered amount of aerosolized spores. The understanding of this comparability is important in order to assess the representativeness of such laboratory-based testing when deciding upon decontamination options for use against Bacillus anthracis spores. Temporal inactivation of B. anthracis surrogate (B. subtilis) spores on representative materials using fumigation with chlorine dioxide, spraying of a pH-adjusted bleach solution, or immersion in the solution was investigated as a function of inoculation method (liquid suspension or aerosol dosing). Results indicated that effectiveness, measured as log reduction, was statistically significantly lower when liquid inoculation was used for some material and decontaminant combinations. Differences were mostly noted for the materials observed to be more difficult to decontaminate (i.e., wood and carpet). Significant differences in measured effectiveness were also noted to be a function of the pH-adjusted bleach application method used in the testing (spray or immersion). Based upon this work and the cited literature, it is clear that inoculation method, decontaminant application method, and handling of non-detects (i.e., or detection limits) can have an impact on the sporicidal efficacy measurements.

Influence of tea and cola on tooth color after two in-office bleaching applications

Aim: To evaluate color changes of teeth after immersion in tea and cola following the application of two in-office bleaching products. Materials and Methods: A total of 60 specimens were obtained from 60 extracted sound human maxillary central teeth. The specimens were randomly divided into three groups (n = 20). Group A was the control group (no bleaching). In Group B, the specimens were bleached with Opalescence Xtra Boost (Ultradent), and in Group C, they were bleached with Smartbleach (High Tech Laser). These groups were then divided into two subgroups (n = 10 in each) according to the colorant solution used: tea and cola. Each bleaching agent was applied to the specimens according to the manufacturer's recommendations. After bleaching, the first color of the specimens was determined with a spectrophotometer according to the CIELAB color system (∆E). Following immersion in the staining solutions, the color was determined after 15 min, 6 h (second day), and 36 h (sixth day), and the color change values were calculated. The results were analyzed statistically by two-way analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) test (P 0.05). In the specimens bleached with Smartbleach, staining in cola solution was greater than tea solution and this difference was statistically significant (P < 0.05). Conclusions: The staining of the bleached specimens was similar in the tea and cola solutions. The bleached specimens showed more staining than the unbleached specimens. The staining of the specimens in the tea and cola increased at all the time intervals evaluated.

Lignocellulolytic activities of crude gut extracts of marine woodborers Dicyathifer mannii and Sphaeroma terebrans

Marine woodborers have a close association with tropical mangrove plants whereby they voraciously consume lignocellulose and play a role in nutrient cycling. They represent a rich source of potential lignocellulolytic enzymes that can be harnessed for conversion of biomass into simple sugars and other monomers for a variety of uses. Ligninolytic enzymes find applications in bio bleaching of pulp and decolouration of textile dyes, whereas cellulolytic and hemicellulolytic enzymes find applications in animal feed, manufacture of bread, bioethanol production and xylitol production among other uses. In this study, we obtained crude gut extracts from two marine woodborers, Dicyathifer mannii (Wright, 1866) and Sphaeroma terebrans (Bate, 1866), from three sampling sites along the Kenyan coast. Lignocellulolytic activities of the gut extracts were investigated in an effort to seek the species with the most lignocellulolytic efficacious extracts. Ligninolytic activities investigated were lignin peroxidase (LiP), manganese-dependent peroxidase (MnP) and laccase (Lac) or monophenol oxidase. Cellulolytic enzymes investigated were glucanases endoglucanase (endo-1-4-β-D-glucanase), exoglucanase (1,4-β-D-glucan-cellobiohydrolase), and β-D-glucosidase or cellobiase (β-D-glucoside glucanohydrolase). Endo-1-4-β-xylanase was investigated in the hydrolysis of xylan, the chief type of hemicellulose. D. mannii crude extracts showed an appreciable Lip activity of up to 34.65±0.116 U/L and endoglucanase (CMCase) activity of up to 50.7 U/ml (1 U represents the amount of enzyme which catalyzed the transformation of 1 micromol of substrate min -1 ). D. mannii is implicated as a source of these enzymes for industrial use.

Operational Use of Household Bleach to “Crash and Release” &lt;I&gt;Aedes aegypti&lt;/I&gt; Prior to &lt;I&gt;Wolbachia&lt;/I&gt;-Infected Mosquito Release

Dengue (family Flaviviridae, genus Flavivirus, DENV) remains the leading arboviral cause of mortality in the tropics. Wolbachia pipientis has been shown to interrupt DENV transmission and is presently being trialled as a biological control. However, deployment issues have arisen on methods to temporarily suppress wild mosquito populations before Wolbachia-infected mosquito releases. By suppressing wild populations, fewer Ae. aegypti releases are required to achieve a sustainable Wolbachia density threshold. Furthermore, public distress is reduced. This study tests the application of domestic bleach (4% NaCIO) to temporarily "crash" immature Aedes populations in water-filled containers. Spray application NaClO (215 ppm) resulted in a mean 48-h mortality of 100, 100, 97, and 88% of eggs, second-instar larvae, fourth-instar larvae, and pupae, respectively. In the field, NaClO delayed ovipositing by 9 d in cooler months, and 11 d in hotter months, after which oviposition resumed in treated receptacles. We found bleach treatment of pot-plant bases did not cause wilting, yellowing, or dropping of leaves in two ornamental plants species. Domestically available NaClO could be adopted for a "crash and release" strategy to temporarily suppress wild populations of Ae. aegypti in containers before release of Wolbachia-infected mosquitoes. The "crash and release" strategy is also applicable to other mosquito species, e.g., Aedes albopictus (Skuse), in strategies using released mosquitoes.

Sequential Photo-bleaching to Delineate Single Schwann Cells at the Neuromuscular Junction

Sequential photo-bleaching provides a non-invasive way to label individual SCs at the NMJ. The NMJ is the largest synapse of the mammalian nervous system and has served as guiding model to study synaptic structure and function. In mouse NMJs motor axon terminals form pretzel-like contact sites with muscle fibers. The motor axon and its terminal are sheathed by SCs. Over the past decades, several transgenic mice have been generated to visualize motor neurons and SCs, for example Thy1-XFP and Plp-GFP mice, respectively. Along motor axons, myelinating axonal SCs are arranged in non-overlapping internodes, separated by nodes of Ranvier, to enable saltatory action potential propagation. In contrast, terminal SCs at the synapse are specialized glial cells, which monitor and promote neurotransmission, digest debris and guide regenerating axons. NMJs are tightly covered by up to half a dozen non-myelinating terminal SCs - these, however, cannot be individually resolved by light microscopy, as they are in direct membrane contact. Several approaches exist to individually visualize terminal SCs. None of these are flawless, though. For instance, dye filling, where single cells are impaled with a dye-filled microelectrode, requires destroying a labelled cell before filling a second one. This is not compatible with subsequent time-lapse recordings. Multi-spectral "Brainbow" labeling of SCs has been achieved by using combinatorial expression of fluorescent proteins. However, this technique requires combining several transgenes and is limited by the expression pattern of the promoters used. In the future, expression of "photo-switchable" proteins in SCs might be yet another alternative. Here we present sequential photo-bleaching, where single cells are bleached, and their image obtained by subtraction. We believe that this approach - due to its ease and versatility - represents a lasting addition to the neuroscientist's technology palette, especially as it can be used in vivo and transferred to others cell types, anatomical sites or species. In the following protocol, we detail the application of sequential bleaching and subsequent confocal time-lapse microscopy to terminal SCs in triangularis sterni muscle explants. This thin, superficial and easily dissected nerve-muscle preparation has proven useful for studies of NMJ development, physiology and pathology. Finally, we explain how the triangularis sterni muscle is prepared after fixation to perform correlated high-resolution confocal imaging, immunohistochemistry or ultrastructural examinations.

Avaliação de Técnicas de Clareamento de Consultório com e sem o Uso de Luz (Laser/Led)

Current research compared two dental bleaching techniques with regard to bleaching and to dental sensitivity degrees. Ten volunteers, involved in the process according to inclusion and exclusion criteria, received a bleaching application of the upper and lower dental arch. Gel from hydrogen peroxide 35% (Whiteness HPMaxx - FGM) was applied by LED (Ultrablue Lazer System IV - DMC Equipments) to the patient’s right side. Three successive applications were carried out every 15 min, totaling 45 min. Bleaching gel Calcium Blue 35% (FGM) was applied to the left superior and inferior dental arches of the patient and kept on the vestibular surfaces during 45 min without any light source. Color scale classical Vita - VITAPAN® and digital images was employed for color evaluation prior to bleaching and after seven days. VAS questionnaire was used to measure sensitiveness prior to bleaching and after seven days of bleaching. Statistical analysis did not reveal any significant color difference between the groups, with or without the light activation of the bleaching gel. Sensitiveness was similar to both groups. Results show that bleaching techniques with or without light provided similar results with regard to bleaching. Patients considered sensitiveness as slight or nil and showed that the method is safe with regard to post-bleaching sensitiveness.

Nanotribological behaviour of tooth enamel rod affected by bleaching treatment

Abstract Tooth enamel is a hybrid organic–inorganic bionanocomposite comprised predominantly of enamel rods. Understanding the effects of bleaching treatment on the biomechanical properties of this tissue is essential for clinical applications. Accordingly, this study is focused on the wear behaviour of the enamel using nanoscratch tests when a 38% hydrogen peroxide bleaching agent was applied. A rounded conical diamond nanoindenter tip (1 μm radius and 45° semiangle) was used to abrade untreated and bleached bovine enamel. Abraded lines of 10 μm length were generated with constant maximum loads ranging from 100 μN to 500 μN. In addition normal and lateral forces were simultaneously measured along the single scratched lines. After the wear tests, the worn areas were scanned by the conical tip to determine the residual profile. Different friction coefficients and wear resistances were obtained depending on the enamel zone and the treatment applied. The work was completed with the determination of mechanical properties by nanoindentation. Elastic modulus, hardness and fracture toughness were obtained to complete the analysis of bleaching agent effect. Variations in the values of elastic modulus and hardness depending on the bleaching treatment have been observed. Additionally, friction coefficients and wear rates were affected by the application of bleaching. After initial increase, the enamel exhibited a recovery of properties when it was stored in artificial saliva.

Highly thermostable xylanase purified fromRhizomucor mieheiNRL 3169

A thermostable xylanase was purified and characterized from the thermophilic fungus Rhizomucor miehei (Cooney & Emerson) Schipper. The enzyme was purified to homogeneity by ammonium sulfate precipitation, sephadex G-100 gel filtration and diethylaminoethyl cellulose anion exchange chromatography with a 29.1-fold. The enzyme was highly active within a range of pH from 5.0 to 6.5. The optimum temperature of the purified enzyme was 75°C. The enzyme showed high thermal stability at 70°C and 75°C and the half-life of the xylanase at 90°C was 30 min. Km and Vmax values at 50°C of the purified enzyme were 0.055 mg/ml and 113.5 μmol min⁻¹ mg⁻¹ respectively. The enzyme was activated by Ca²+, Cu²+, K+ and Na+. On the other hand, Ag²+, Hg²+, Ba²+, and Zn²+ inhibited the enzyme. The molecular weight of the xylanase was estimated to be 27 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The present study is among the first works to examine and describe a secreted highly thermostable endoxylanase from the Rhizomucor miehei fungus. This enzyme displays a number of biochemical properties that make it a potentially strong candidate for industrial and commercial application in pulp bleaching.

Isolation and Dye Decolorization of a &lt;i&gt;Bacillus subtilis&lt;/i&gt; Strain LS02 Exhibiting Laccase Activity

A newly isolated strain LS02 was estimated for its ability in dye decolorization. The LS02 strain was identified as Bacillus subtilis by the combination of physicochemical tests and 16S rDNA sequence analysis. The isolated strain could oxidize the laccase substrate syringaldazine, indicating the existence of laccase activity. B. subtilis LS02 grown well in the pH range of 5.0~9.0, and showed an optimum growth temperature at 37°C. Indigo carmine could be completely decolorized by B. subtilis LS02 after 4 days, whereas Remazol Brilliant Blue R, reactive black 5 and crystal violet were poorly decolorized. The result indicated that the laccase of B. subtilis LS02 may be suitable for the application in textile bleaching of indigo carmine.