Esterification of used vegetable oils using the heterogeneous WO3/ZrO2 catalyst for production of biodiesel.

Tungsten oxide zirconia, sulfated zirconia and Amberlyst-15 were examined as a catalyst for a conversion of used vegetable oils (VOs) to fatty acid methyl esters (FAMEs). Among them, tungsten oxide zirconia was a promising heterogeneous catalyst for the production of biodiesel fuels from used VOs because of high activity in the conversion over 93% and no leaching WO(3) in the esterification reaction. The reaction conditions were optimized. A study for optimizing the reaction parameters such as the reaction temperature, stirring speed, WO(3) loading over ZrO(2) and reaction time, was carried out. The catalyst was characterized by BET, XRD, FT-IR, and NH(3)-TPD. With increasing WO(3) loading over ZrO(2), the triclinic phase of WO(3) increased and the tetragonal phase of zirconia was clearly generated. The highest acid strength of 20 wt% tungsten oxide zirconia catalyst was confirmed by NH(3)-TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction.

High-sensitivity detection for model organophosphorus and carbamate pesticide with quartz crystal microbalance-precipitation sensor.

The effect of acetylcholinesterase (AChE) immobilization over the surface of a quartz crystal microbalance (QCM), by chemisorption of the AChE thiolated with a heterobifunctional cross-linker, sulfo-succinimidyl-6-[3-(2-pyridyldithio)propionamido]hexanoate, and carboxyl-amine coupling of AChE to 3-mercaptopropionic acid self-assembled monolayer, on the responses of a batch-type QCM-precipitation sensor was compared, resulting in a better sensitivity and binding efficiency in the former method. When an inhibition study with the developed sensor was undertaken at the optimized AChE immobilization with varying concentrations of a model organophosphorus pesticide EPN and carbamate one carbofuran, a sensitive detection for them was possible with the limit of detection corresponding to 1.55 x 10(-8) and 1.30 x 10(-9)M, respectively.

Development of a chemiluminescent immunosensor for chloramphenicol.

A direct competitive chemiluminescent immunosensor system that exploits the competition between chloramphenicol (CAP) as an analyte and CAP-horseradish peroxidase conjugate as a tracer for binding to an anti-CAP antibody on a solid support was devised by installing a flow-through cell which was connected to an injector and a peristaltic pump inside a dark box, followed by positioning a photomultiplier tube as light detector in front of it. The anti-CAP antibody was immobilized onto positively charged Biodyne B membrane pieces by a dipping procedure. The operating conditions for the immunosensor were selected with respect to substrate composition (0.25, 13.3 and 0.66 mM for luminol, H2O2 and p-iodophenol, respectively), injection volume of the substrate solution (200 microL) and the concentrations of antibody for immobilization (0.10 mg mL(-1)) and tracer (0.030 mg mL(-1)). At these conditions, sensor response according to analyte concentration was well fitted to a linear equation when plotted in semi-logarithmic scale, with the limit of detection for CAP of 10(-8) M. By using the immunosensor, CAP measurement in the model samples prepared from five food materials was conducted.

Application of a taste evaluation system to the monitoring of Kimchi fermentation.

As an objective method, taste evaluation with an instrument is able to supplement the subjective sensory evaluation and to be applied to the optimization of food processing. Kimchi, a Korean traditional pickle fermented with lactic acid bacteria, is expanding its consumption worldwide. The fermentation control of it has been routinely done by measuring titratable acidity and pH. In this study, an eight-channel taste evaluation system was prepared, followed by an application to the monitoring of Kimchi fermentation. Eight polymer membranes which individually responded to cationic or anionic substances were prepared by mixing electroactive materials such as tri-n-octylmethylammonium chloride, bis(2-ethylhexyl)sebacate as the plasticizer and polyvinyl chloride in the ratio of 1:66:33. Each membrane prepared was separately installed onto the sensitive area of an ion-selective electrode to produce the respective taste sensor. The eight-channel sensor array and a double junction reference electrode were connected to a 16-channel high input impedance amplifier. The amplified sensor signals were stored to a personal computer via a multi-channel A/D converter. Two sensor groups composed of the cation-selective and anion-selective polymer membrane electrodes showed characteristic concentration-dependency to various artificial taste substances. As a whole, the response potentials of the sensor array increased during the fermentation period at 4, 10 and 25 degrees C. Even the response potentials of the anion-selective taste sensors slightly increased possibly due to the protonation of anions by liberated H+ ions, thereby leading to a decrease in the anion concentration. When the signal data were interpreted by principal component analysis (PCA), the first PC at 4 degrees C explained most of the total data variance. A close correlation was found between the values of titratable acidity and the first PC, which indicated a possible applicability of the multi-channel taste sensor of this study to the process monitoring of various pickle.

Development of a direct-binding chloramphenicol sensor based on thiol or sulfide mediated self-assembled antibody monolayers.

A batch-type antibody-immobilized quartz crystal microbalance (QCM) system for detecting chloramphenicol (CAP) was developed. To bind an anti-CAP antibody onto the gold electrode surface of piezoelectric crystals, self-assembled monolayers (SAMs) of different thiols or sulfides were formed by a chemisorption procedure. Then, the anti-CAP antibody was covalently linked to the pre-formed monolayers by an activation procedure using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysulfosuccinimide. The antibody-immobilized QCM chip thus prepared was installed in a well holder and was measured for sensor response. Compared with the bare QCM chip and the QCM chip only coated with 3-mercaptopropionic acid (MPA), the antibody-immobilized sensor showed greatly enhanced frequency shifts by 10-50-fold after CAP injection. In this case, CAP detection which was indicated by steady-state resonant frequency shift was accomplished within 10 min. When CAP solution was injected into the reaction cell in 50mM concentration, the frequency shifts obtained were, respectively, 530 and 505 Hz in case of thiosalicylic acid and MPA immobilization. Repeated use of the sensor chips up to eight times was possible after 1 min regeneration with 0.1M NaOH. This system demonstrated a potential application of thiol or sulfide mediated SAMs as the pre-coatings of a real-time detection on CAP in solution.

Application of a flow-type antibody sensor to the detection of Escherichia coli in various foods.

A flow-type biosensor system which uses a broad-spectrum anti-Escherichia coli antibody and quartz crystal microbalance as biological component and transducer was developed. Biosensor responses were initiated by injecting viable E. coli suspensions through a flow cell and the sensor system was optimized for response time according to flow rate and injection time, followed by the measurement of responses for various E. coli strains. As expected, the sensor system showed a characteristic broad binding feature against E. coli strains. A linear sensor response in double-logarithmic scale was observed for the microbial suspensions ranging from 1.7 x 10(5) to 8.7 x 10(7) CFU/ml. Sample measurements could be done within 20-30 min after Stomacher treatment followed by spiking or enrichment.