Orathai Pornsunthorntawee

Purification and concentration of a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa SP4 using foam fractionation

Pseudomonasaeruginosa SP4 was cultivated to produce a rhamnolipid biosurfactant from a nutrient broth with palm oil. The foam fractionation technique in batch mode was used for the recovery of the excreted biosurfactant from the free-cell culture medium. The effects of air flow rate, initial foam height, the pore size of the sintered glass disk, initial liquid volume, and operation time on the process performance were studied. The results showed that the operating conditions were optimized at an air flow rate of 30 ml/min, an initial foam height of 60 cm, a pore size of the sintered glass disk in the range of 160-250 microm (No. 0), an initial liquid volume of 25 ml, and an operation time of 4 h, providing a biosurfactant recovery of 97% and an enrichment ratio of 4. The HPLC results also indicated that the rhamnolipid was concentrated by using the foam fractionation technique.

Solution properties and vesicle formation of rhamnolipid biosurfactants produced by Pseudomonas aeruginosa SP4.

A biosurfactant produced by Pseudomonas aeruginosa strain SP4 was previously reported as a mixture of 11 types of rhamnolipid compounds. Among them, the major component in the biosurfactant was characterized as l-rhamnosyl-3-hydroxydecanoyl-3-hydroxydecanoate, or monorhamnolipid (Rha-C(10)-C(10)). In this present study, solution properties of the biosurfactant were investigated in a phosphate-buffer saline (PBS) solution (pH 7.4) by using surface tension, turbidity, electrical conductivity, and dynamic light scattering (DLS) measurements. It was found that spherical biosurfactant vesicles of various sizes (ranging from 50 to larger than 250 nm) were spontaneously formed at a biosurfactant concentration greater than its critical micelle concentration (CMC), which was 200mg/l. The encapsulation efficiency (E%) of the biosurfactant vesicles was preliminarily studied by using Sudan III, a water-insoluble dye, as a model hydrophobic substance. The obtained results showed that the vesicle formed in the PBS solution at a biosurfactant concentration of 1280 mg/l could entrap about 10% of the initial hydrophobic dye concentration. The effects of salt and alcohol on the vesicle formation of the biosurfactant and its encapsulation efficiency were also observed by using sodium chloride (NaCl) and ethanol (C(2)H(5)OH), respectively. In the presence of either NaCl or C(2)H(5)OH, the vesicle size was reduced from larger than 250 nm to 50-250 nm. The encapsulation efficiency of the biosurfactant vesicle was slightly influenced by the addition of NaCl, but was significantly increased, up to nearly 30%, in the presence of C(2)H(5)OH.

Biosurfactant production by Pseudomonas aeruginosa SP4 using sequencing batch reactors: effects of oil loading rate and cycle time.

In this present study, sequencing batch reactors (SBRs) were used for biosurfactant production from Pseudomonasaeruginosa SP4, which was isolated from petroleum-contaminated soil in Thailand. Two identical lab-scale aerobic SBR units were operated at a constant temperature of 37 degrees C, and a mineral medium (MM) with palm oil was used as the culture medium. The effects of oil loading rate (OLR) and cycle time on the biosurfactant production were studied. The results indicated that the optimum conditions for the biosurfactant production were at an OLR of 2 kg/m(3)days and a cycle time of 2 days/cycle, which provided a surface tension reduction of 59%, a chemical oxygen demand (COD) removal of 90%, and an oil removal of 97%. Under the optimum conditions, it was found that the biosurfactant production was maximized at an aeration time of 40 h. These preliminary results suggest that the SBR can potentially be adapted for biosurfactant production, and perhaps further developed, potentially for large-scale biosurfactant production.

Depolymerization of chitosan-metal complexes via a solution plasma technique.

Chitosan-metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag(+), Zn(2+), Cu(2+), and Fe(3+) ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu(2+) or Fe(3+) ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan-Ag(+) and chitosan-Zn(2+) complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan-metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan-Fe(3+) complex with the plasma treatment time of 180 min.

Rhamnolipid biosurfactants: production and their potential in environmental biotechnology.

Certain species of Pseudomonas are able to produce and excrete a heterogeneous mixture of biosurfactants with a glycolipid structure. These are known as rhamnolipids. In the biosynthetic process, rhamnolipid production is governed by both the genetic regulatory system and central metabolic pathways involving fatty acid synthesis, activated sugars and enzymes. These surface-active compounds can be produced from various types of low-cost substrates, such as carbohydrates, vegetable oils and even industrial wastes, leading to a good potential for commercial exploitation. By controlling environmental factors and growth conditions, high rhamnolipid production yields can be achieved. Rhamnolipids provide good physicochemical properties in terms of surface activities, stabilities and emulsification activities. Moreover, these surface-active compounds exhibit antimicrobial activities against both phytopathogenic fungi and bacteria. Due to an increase in concerns about environmental protection and the distinguishing properties of the rhamnolipids, it seems that rhamnolipids meet the criteria for several industrial and environmental applications, such as environmental remediation and biological control. Rhamnolipids have already been commercially produced, making them more economically competitive with synthetic surfactants. In the near future, rhamnolipids may be commercially successful biosurfactants.

Characterization and encapsulation efficiency of rhamnolipid vesicles with cholesterol addition.

The effect of cholesterol on the vesicle formation of a rhamnolipid biosurfactant extracted from the liquid culture of Pseudomonas aeruginosa SP4 was investigated. The rhamnolipid vesicles were prepared in a phosphate-buffer saline (PBS) solution (pH 7.4) at a biosurfactant concentration of 2.6mM, or 6.5 times the critical micelle concentration (CMC), with various amounts of cholesterol. The biosurfactant solution was characterized using turbidity, zeta potential, and dynamic light scattering (DLS) measurements. The morphology of the rhamnolipid vesicles formed at different cholesterol concentrations was examined with the use of transmission electron microscopy (TEM). The results showed that the rhamnolipid biosurfactant formed spherical vesicles both in the absence and presence of cholesterol, but the incorporation of the cholesterol into the bilayer membrane reduced the vesicle size. Sudan III, a water-insoluble dye, was used as a model hydrophobic compound in the encapsulation experiment. The encapsulation efficiency (E%) of the rhamnolipid vesicles was affected by the cholesterol concentration and the initial Sudan III concentration. The maximum E% of nearly 90% was achieved at the cholesterol concentration of 100μM and the initial Sudan III concentration of 8.8μM.

Purification of Single-Walled Carbon Nanotubes (SWNTs) by Acid Leaching, NaOH Dissolution, and Froth Flotation

The SWNTs with a carbon content of approximately 3% were synthesized via the disproportionation of CO over a CoMo/SiO2 catalyst. The three sequential steps, including acid treatment, silica dissolution, and froth flotation, were proposed for the purification of the as-synthesized SWNTs. The pretreatment step for the catalyst removal by acid leaching was optimized at an HCl concentration of 6 M, 50°C, and a sonication time of 3 h, corresponding to the Co and Mo removals of 84% and 44%, respectively. For the silica dissolution, the SWNTs sample after the acid leaching step was treated with a 5 M NaOH solution at 50°C and a sonication time of 3 h, leading to a silica removal of 54%. The froth flotation was employed to separate the SWNTs from the remaining silica using SDBS as an anionic frother. The process performance was maximized at an SDBS concentration of 0.1 × CMC, an air flow rate of 120 cm3/min, and a solution pH of 5, yielding a carbon content of the purified SWNTs of 71%. It was also found that the proposed technique successfully purified the as-synthesized SWNTs sample without damaging its nanostructure.

Recovery of Surfactant from an Aqueous Solution Using Continuous Multistage Foam Fractionation: Mixed Surfactant System

A continuous multistage foam fractionation column with bubble caps was used for surfactant recovery from mixed surfactant solutions containing polyethylene glycol tert-octylphenyl (OPEO10) and cetylpyridinium chloride (CPC) and the effects of air flow rate, foam height, and feed flow rate were investigated under a steady state of conditions. For the mixed surfactant system, the effect of synergism in the surfactant adsorption density was found. For separation efficiency, the total residual factor remained unchanged with an increasing feed molar fraction of OPEO10 (α), suggesting that the addition of OPEO10 does not increase the total separation efficiency. The residual factor of CPC increased with an increasing molar fraction of OPEO10 (α), while the residual factor of OPEO10 was lower for the mixed surfactant systems. A competitive removal was found in that the OPEO10 can compete with CPC for the bubble surface. The total separation factors and enrichment ratio of mixed surfactant systems were in-between the two single surfactant systems at a long foam residence time and, in contrast, showed antagonism at short foam residence. This is due to the difference in liquid entrainment in foam at long and short foam residence times.

CHAPTER 11:Silk Fibre Composites

Silk fibers, animal-based protein fibers, are composed of two fibroin protein filaments embedded in sericin, a glue-like protein coating. The exploitation of silk fibers as sutures and textiles has been done for centuries and industrial-scale production of silk fibers has further expanded their utilization. At present, both silk fibers and their protein component, known as regenerated silk fibroin, can be effectively used as either matrices or biofillers/reinforcements for the fabrication of composite materials because of their remarkable characteristics in terms of mechanical properties, degradability, and biocompatibility. The silk-based composites can be prepared in several forms, including fibers, films, and sponges or scaffolds. In recent years, silk-based composites have gained much more attention as one of the most promising candidates for use in various fields, such as technical textiles, structural applications, biosensors, biomedical applications, tissue engineering, and drug delivery systems. Since the incorporation of either the silk fibers or the regenerated silk makes the fabricated composites “greener”, silk-based composites should be potential alternatives to traditional composites on the basis of an environmentally friendly viewpoint.