Separation of the protease enzymes of Bacillus licheniformis from the fermentation medium by crossflow ultrafiltration

The separation from fermentation medium of extracellular serine alkaline protease (SAP) enzyme produced by Bacillus licheniformis was investigated using a crossflow ultrafiltration system. SAP was separated from the high molecular weight neutral protease (NP) and amylase (AMY) enzymes and from the low molecular weight organic acids and amino acids in a crossflow ultrafiltration system with 30 000 Da and 10 000 Da MWCO polysulfone membranes, respectively. The effects of transmembrane pressure (TMP), recirculation velocity (v), and initial enzyme concentration (C_E) on the permeate flux, on the activities of SAP, NP and AMY enzymes, and on the recovery of SAP were investigated. High permeate flux was obtained at high recirculation velocity and TMP, but at low initial enzyme concentration. SAP enzyme recovery and activity measured in the system also showed alterations with hydrodynamic conditions. The best operation conditions for the separation of SAP from NP and AMY were TMP = 20 kPa, v = 0.50 ms⁻¹ and C_E = 0.28 gdm⁻³. The separation of SAP from the organic and amino acids was best performed at TMP = 100 kPa, v = 0.33 ms⁻¹ and C_E = 0.40 gdm⁻³. © 2000 Society of Chemical Industry     

Mat formation and unstable flows of highly filled suspensions in capillaries and continuous processors

Suspensions, which are filled at loading levels approaching their maximum packing fractions, present special processing challenges. The flow and deformation behavior of such highly filled suspensions are dominated by strong slip effects. Furthermore, during pressure driven flows of these suspensions, the polymer matrix can filter out, giving rise to demixing and unstable flows. In this study, the capillary flow and extrusion of highly filled suspensions of ammonium sulfate and other salt fillers in a poly(butadiene acrylonitrile acrylic acid), PBAN matrix were investigated. The experimentally observed instabilities were elucidated in conjunction with a proposed mechanism, involving slip and filtration rates. This mechanism suggested greater affinity to unstable flows with relatively lower matrix shear viscosity, greater particle size of the filler, and greater convergence ratio; all of which were experimentally verified.     

Effects of using combined essential oils on quality parameters of bio‐yogurt

Present study aims to develop a new type of probiotic yogurt with ginger and chamomile essential oils (EOs) at therapeutic levels (0.2 and 0.4%) by evaluating its some physical, chemical, microbiological and sensory characteristics. Probiotic types of yogurt samples and those with 0.4% ginger EO gave the largest counts of viable probiotic bacteria in the rates of 8.32 cfu/g and 8.01 cfu/g, respectively. It gave larger syneresis rate (8.64 mL/25 g) on the first day than the rest of the samples while C1 (only probiotic strain with direct vat set starter culture) sample represented the lowest rate (5.9 mL/25 g) on day 21. Among the samples with various contents, C2 (inoculated probiotic strain with 0.2% essential oil ginger) and C3 (inoculated probiotic strain with 0.4% essential oil ginger) were found to be organoleptically the most acceptable with close scores to that of control.

Practical applications

Antibacterial and antioxidant activities of essential oils have received considerable attention in food preservation. During bio‐yogurt storage, the edible film incorporating ginger and chamomile essential oils showed reducing effect on the microbial growth and extended the shelf‐life of samples.     

Impact modified epoxy/montmorillonite nanocomposites: synthesis and characterization

Diglycidyl ether of bisphenol A type epoxy resin-polyether polyol-organically treated montmorillonite ternary nanocomposites were synthesized in this study. The effects of addition of polyether polyol as an impact modifier on morphological, thermal and mechanical properties of nanocomposites were investigated by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, impact and tensile testing. The results showed that organically treated montmorillonite is intercalated by epoxy, since the interlayer spacing expanded from 1.83 to 3.82 nm upon nanocomposite synthesis. The addition of polyether polyol impact modifier had no effect on the interlayer spacing. SEM examination showed that polyol forms an immiscible phase in the epoxy matrix. Thermal characterization of nanocomposites indicated an increase in T_g with respect to both polyether polyol and montmorillonite contents. The impact strength of the samples with no clay was improved approximately 160% upon adding 7 wt% polyether polyol. In polyether polyol modified nanocomposites, the impact and tensile strengths decreased with respect to increasing amount of montmorillonite and showed a maximum with respect to the polyether polyol content at constant clay loading. The Young's modulus of the nanocomposites exhibited an increase with respect to the montmorillonite loading and showed a maximum with respect to the polyol content at each clay loading.     

Single-edge monotonic sequences of graphs and linear-time algorithms for minimal completions and deletions

We study graph properties that admit an increasing, or equivalently decreasing, sequence of graphs on the same vertex set such that for any two consecutive graphs in the sequence their difference is a single edge. This is useful for characterizing and computing minimal completions and deletions of arbitrary graphs into having these properties. We prove that threshold graphs and chain graphs admit such sequences. Based on this characterization and other structural properties, we present linear-time algorithms both for computing minimal completions and deletions into threshold, chain, and bipartite graphs, and for extracting a minimal completion or deletion from a given completion or deletion. Minimum completions and deletions into these classes are NP-hard to compute.     

Effects of cationic liposome-DNA complexes on pulmonary surfactant function in vitro and in vivo

Cationic liposome-DNA complexes are being evaluated as potential gene therapy agents for the lung. Cations have strong effects on the biophysical functions of lung surfactant. Therefore, we assessed whether cationic liposomes [composed of N-(1-(2,3-dioleyloxy) propyl)-N,N,N-trimethyl-ammonium chloride and dioleylphosphatidylethanolamine] with or without DNA affect behavior of four types of surfactant in vitro. Experiments were carried out using a modified Wilhelmy surface balance. The ability of surfactants that contain protein and anionic lipids to lower surface tension was inhibited in the presence of cationic liposomes. Inactivation was less when DNA was preincubated with cationic liposomes. Surfactant that contained neither protein nor anionic lipids was not inactivated. Mechanical properties of the lung were studied to assess in vivo surfactant function after intratracheal instillation of a cationic liposome-DNA complex into adult rats. Pressure-volume deflation curves were shifted by 18% compared with those from normal (untreated) animals, but this effect was transient and not different from that observed in animals who received a similar volume of saline. These findings indicate that cationic liposomes alone may have deleterious effects on behavior of some surfactants possibly by disrupting charge interactions between negatively charged phospholipids and surfactant proteins. When DNA is added to liposomes before exposure to surfactants, the adverse charge interactions may be obviated by charge neutralization of liposomes by DNA.     

Viscoelastic properties of reactive and non‐reactive blends of ethylene‐methyl acrylate copolymers with styrene‐maleic anhydride copolymer

The effects of compatibilizing reactions on the viscoelastic properties and morphology of ethylene‐methyl acrylate copolymers were studied. Potentially reactive blends of styrene‐maleic anhydride copolymer (SMAH) and a terpolymer of ethylene/methyl acrylate/glycidyl methacrylate (E‐MA‐GMA) were compared with a non‐reactive blend of SMAH and an ethylene/methyl acrylate (E‐MA) copolymer with similar rheological properties. Melt mixing was carried out in a batch mixer and in a co‐rotating twin screw extruder. The morphology of the reactive blends showed smaller domain sizes than the non‐reactive blends, and the viscoelastic properties of the blends were very different. The storage and loss moduli and the complex viscosity of the reactive blends were greater than those of non‐reactive blends. The reactive blends had a higher zero shear viscosity, plateau modulus and mean relaxation time than their non‐reactive counterparts, indicating a higher degree of melt elasticity. The melt elasticity was maximum at 25% functionalized ethylene‐methyl acrylate concentration.     

Multichromic conducting copolymer of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole with EDOT

Despite the significant progress made in the field of electrochromic polymers, the multichromic facility of current knowledge is restricted. Therefore, as previously proven, electrochemical copolymerization of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole (SNBS) and 3,4-ethylenedioxythiophene (EDOT) was used as a strategy to achieve desired multichromic properties, where the resultant copolymer displayed distinct color changes between claret red, yellow, green, and blue colors with short switching times and high optical contrast. As an application, absorption/transmission type electrochromic device with indium tin oxide (ITO)/copolymer/gel electrolyte PEDOT/ITO configuration was constructed, where copolymer and PEDOT functioned as the anodically and the cathodically coloring layers, respectively. Results implied the successive use of this copolymer in electrochromic device applications, since the device exhibited short switching times with a wide color variation upon applied potential.     

Polystyrene–organoclay nanocomposites prepared by melt intercalation,in situ,and masterbatch methods

In this study, polystyrene (PS)/montmorillonite nanocomposites were prepared by melt intercalation, in situ polymerization, and masterbatch methods. In the masterbatch method, as the first step, a high clay content composite of PS–organoclay (masterbatch) was prepared by in situ polymerization, and then the prepared masterbatch was diluted to desired compositions with commercial PS in a twin‐screw extruder. The structure and mechanical properties of the nanocomposites were examined. X‐ray diffraction (XRD) analysis showed that the d‐spacing of the in situ formed nanocomposites increased from 32.9 Å for the organoclay powder to 36.3 and 36.8 Å respectively in nanocomposites containing 0.73 and 1.6 wt% organoclay, indicating intercalation. However, the d‐spacing of the other prepared materials remained nearly unchanged when compared with pure organoclay powder. Thus, at these low clay contents, in situ formed nanocomposites showed the best improvement in mechanical properties including tensile, impact strength, and Young's modulus. In situ polymerization method did not prove to be efficient at high clay loadings in terms of intercalation and mechanical properties. At high clay loadings, the effects of the three methods in promoting mechanical properties were not significantly different from each other. POLYM. COMPOS., 27:249–255, 2006. © 2006 Society of Plastics Engineers     

Occurrence, oral exposure and risk assessment of volatile organic compounds in drinking water for Izmir

Concentrations of volatile organic compounds (VOCs) were measured in the drinking water in Province of Izmir, Turkey, and associated health risks due to ingestion of these compounds were investigated using population weighted random samples. A total of 100 houses were visited in different districts of Izmir and drinking water samples were collected from consumers' drinking water source. Questionnaires were administered to one participant in each house to determine demographics and drinking water consumption rates. Oral exposure and risks were estimated for each participant and Izmir population by deterministic and probabilistic approaches, respectively. The four trihalomethane (THM) species (i.e., chloroform, bromodichloromethane, dibromochloromethane, and bromoform), benzene, toluene, p-xylene, and naphthalene were the most frequently detected VOCs with concentrations ranging from below detection limit to 35 microg/l. The risk estimates were found to be less than the values reported in the literature with few exceptions. Noncarcinogenic risks attributable to ingestion of VOCs for Izmir population were negligible, whereas the mean carcinogenic risk estimates for bromodichloromethane and dibromochloromethane were above the de minimis level of one in a million (10(-6)). For all VOCs, the concentrations measured in metropolitan area were greater than those in other districts. All THM species were detected in higher concentrations in tap water, whereas nontap water contained more benzene, toluene, p-xylene, and naphthalene. Therefore, the concentrations of the latter four compounds and associated risks increased with increasing income and education level since bottled water was used in larger proportions within these subgroups. The results of this study showed that oral exposure to drinking water contaminants and associated risks may be higher than the acceptable levels even if the concentrations fall below the standards.