Application of chitosan–alginate microspheres for the sustained release of bacteriophage in simulated gastrointestinal conditions

This study was designed to evaluate the acid stability, release property and antimicrobial efficacy of Escherichia coli O157:H7 bacteriophages encapsulated in chitosan–alginate microspheres under the simulated gastrointestinal conditions. The bacteriophages belonging to Myoviridae family were stable at the pH above 4 in trypticase soy broth. The chitosan–alginate microspheres exhibited protective effect on the viability of bacteriophages in the simulated gastric conditions at pH 2.0 and pH 2.5, showing 4.8 and 5.6 log PFU mL^‐1, respectively, after 1 h of incubation at 37 °C. The release per cent of bacteriophages from microspheres gradually increased up to 65% in the simulated intestinal condition (pH 7.5) at 37 °C for 6 h. The lytic efficacy of chitosan‐ and alginate‐encapsulated bacteriophages against E. coli O157:H7 was significantly maintained in the simulated intestinal conditions to 10 h of incubation (1.3 log reduction). The results suggest that the chitosan–alginate microspheres can be used as a reliable delivery system for bacteriophages.     

Clarification of a wheat straw‐derived medium with ion‐exchange resins for xylitol crystallization

BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry     

Model study of the crosslinking of polydimethylsiloxanes by peroxides

The decompositions of di-t-butyl peroxide (TBP) and diaroyl peroxides in permethylated silicone oil (47V20) have been studied by differential scanning calorimetry (DSC). Results show the importance of the solubility of the peroxide in the silicone on their rate of disappearance. For the diaroyl peroxides, according to the nature of the substituents on the phenyl ring and the concentration of the peroxide, the decomposition occurs in solution and/or in the solid phase. Decomposition in solution began at a lower temperature than in the solid phase, which took place immediately after melting and was quite instantaneous. Decomposition of these peroxides was also performed in octamethylcyclotetrasiloxane (D₄) and decamethyltetrasiloxane (DMTS). According to DSC results, D₄ seems to be a better model of the silicone than the linear one. Analyses of the products of the decomposition of TBP and dibenzoyl peroxide (BP) in this model showed that the dehydrodimer of D₄ was produced in low yield relative to peroxide. The main compounds obtained were high molecular weight compounds, which were apparently different for the two peroxides. The free radical origin of these products has been proven in the case of TBP by the addition of TEMPO in the reaction medium.     

In-Situ and Real-Time Investigation of Columnar-to-Equiaxed Transition in Metallic Alloy

In this article, we present a review of observations during Al-3.5 wt pct Ni alloy solidi.cation experiments performed at the European Synchrotron Radiation Facility (ESRF) in Grenoble. These experiments provide direct access to dynamical phenomena during columnar growth (initial transient and breakdown of a planar solid-liquid interface), and for the first time to the transition from columnar-to-equiaxed microstructure (nucleation ahead of a columnar front and blocking of a columnar front by an equiaxed microstructure) and fully equiaxed growth (propagation of an effective front). Based on these experimental observations, critical parameters such as columnar growth velocity variation during the transition or equiaxed-grain diameter are measured and discussed. This article is based on a presentation made in the symposium entitled “Solidi.cation Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.