New Microorganism Detection Methods Introduced

This month’s lab column covers several recently introduced testing techniques. These include microorganism detection using luminescence, volatile amine detection, and measurement of chocolate coating viscosity.

Listeria Detection without Amplification Step
A French company, EuroProbe, is seeking to distribute in North America its new LumiProbe 24 test for Listeria and Salmonella contamination in food products. The test is said to be immune to false positives, as there is no PCR amplification step to allow introduction of foreign nucleic acids, and in principle can detect a single bacterium. This is said to make it useful for food processing companies working with meat, dairy, and seafood products that need to demonstrate an absence of bacterial contamination.

The technique is based on solid-phase sandwich hybridization with luminescent detection. It is claimed that the technique can detect targeted bacteria in less than 24 hr, most of which time is taken up by culture of the original sample in an enrichment broth. The test itself requires four steps and takes 2 hr. The procedure begins with sampling of the enrichment broth and lysis of the bacteria in it. The lysed sample is then placed in a test tube (for small-scale testing) or in a well of a microtiter plate. The tube or well has been previously coated with a DNA oligonucleotide complementary to a region on the ribosomal RNA of the target bacteria. Use of the ribosomal RNA, which is present in thousands of copies per cell, greatly increases the sensitivity of the assay.

The RNA bound by this “capture probe” is then further hybridized with another DNA oligonucleotide, a “reading probe,” that is fluorescein-labeled and binds to a different region of the rRNA. This requirement for binding to two distinct and unique regions of the rRNA makes the technique specific for the target bacteria. An antifluorescein antibody conjugated to alkaline phosphate is bound to the reading probe. A standard substrate that becomes luminescent when acted on by alkaline phosphatase therefore demonstrates the presence of the capture probe– rRNA-reading probe sandwich.

After all unbound nucleic acids and excess reagents are washed away, the test tube or plate is read using a standard chemiluminometer. Since the luminescence is permanent, the sample results can be examined later or stored as a permanent record. The procedure is currently in use in the European Union. Approval by the Food and Drug Administration has not yet been applied for.

For more information, contact EuroProbe, SA, Le Gemellyon Nord, 57, Boulevard Vivier Merle, 69429 Lyon Cedex 03, France (phone 011-33-4-72-68-71-78; fax 011-33-4-72-68-71-77) —or circle 309.

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New Rapid Detection of Salmonella in Foods
Salmonella is present in the environment and in the gastrointestinal tract of animals and humans. Approximately 800,000 to 4 million cases of salmonellosis occur in the U.S. yearly, according to the Centers for Disease Control and Prevention.

Gene-Trak Systems, a manufacturer of food diagnostics, has introduced a new rapid system for detecting Salmonella spp. in foods. Gene-Trak’s Sequepoint™ Salmonella uses DNA hybridization technology in a microtiter format that can be used manually or with an automated processor for high throughput of microbiological analysis of food samples.

The new system is a DNA probe assay specifically designed for the rapid detection of Salmonella spp. in foods. According to the company, utilization of directly labeled probes provides sensitivity and specificity equivalent to the company’s DLP assay and traditional culture methods. The assay is capable of detecting as few as one Salmonella cell in 25 g of food sample. The combination of DNA hybridization technology in a 96-well microtiter format is said to offer flexibility and convenience.

For more information, contact Gene-Trak Systems, 94 South St., Hopkinton, MA 01748 (phone 508-435-7400; fax 508-435-0025) —or circle 310.

Tags Detect Food Decomposition
Cox Technologies is offering a tag to detect decomposition in foods, such as seafood. The tags, called FreshTags®, are color indicators which sense the production of gases known as volatile amines. These compounds produce the familiar “fishy odor” that is common to all seafood. The odor-causing chemicals react with the patented, nontoxic food dye–based indicator inside the tag and gradually produce a color reaction, indicating that the seafood is past the point of usable freshness.

The tags were developed by FDA scientists working at the Jefferson National Laboratory in Jefferson, Ark. Dwight Miller and Jon Wilkes, inventors of the technology behind the tags, worked for several years to create a simple, inexpensive, and effective way for consumers and food retailers to know what is happening with the seafood they store and prepare. The tag has been tested at the University of Florida and at the Jefferson National Laboratory. It is effective for all types of shrimp and shellfish and most types of cold-water, white-fleshed finfish.

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The tags are adhesive labels which are attached to packages of seafood in a way that allows the gas space of the package to touch the reactive dot of the tag. The dots are printed elements that contain the proprietary chemicals that cause the volatile amines to change dot color. The tags warn of impending problems with decomposition of the seafood product, and their sensitivity can be adjusted to signal the right action to be taken with a certain type of seafood package.

The tags’ chemical system can also be embedded in flexible polymer films. There are several possibilities for their use in packaging. The technology is adaptable to volatile acid detection, as well. Volatile acids are produced by a wide variety of salad preparations and minimally prepared vegetables. The system, tag types, and application mechanisms are being tested by the National Marine Fisheries Service and several university and private industrial laboratories.

The company has released a professional testing kit based on the technology. The F-1 Rapid Detection Kit allows food industry professionals to detect early decomposition in almost any high-protein prepared or whole food product. It is useful for laboratories in food processing operations, seafood purchasing, inspection of incoming materials and in commissary operations with highly prepared food items subject to extended portion removal. The kit performs a generalized test for protein breakdown during food composition. It was originally set up to detect decomposition in whole shrimp, but can be used for any other application where a volatile amine signal is available. Decision-point setting will rely on determination of the level of signal that corresponds to a sensory-based good or bad product. The test takes about 12 min to perform. For more information, contact Cox Technologies, 69 McAdenville Rd., Belmont, NC 28012 (phone 800-848-9865; fax 704-825-4498; www.coxtec.com) —or circle 311.

New Chocolate Viscosity Application
Brookfield Engineering Laboratories, Inc., has released information on a new chocolate-coating viscosity-measurement application According to a application note by Alejandro Tomato, for the past 50 years or so, the confectionery industry in the U.S. has primarily relied on the Mac-Michael Viscometer to measure chocolate coating viscosity. The instrument has several disadvantages, but has not been replaced because other instruments are not easily correlated to it. Brookfield’s Model HAT Viscometer is said to offer significant improvements over the Mac-Michael unit and correlate well with it.

Different varieties of chocolates having a range of flow properties are used for “enrobing,” and for making “blocks.” In the viscosity measurement of chocolate products, it is common to describe the flow properties using the Casson flow curve, which incorporates the following parameters: The yield value, which is the shear stress that must be exerted to initiate flow in any product; in chocolate, this value relates to the coating or decorating characteristics. Plastic viscosity, which is a function of the shear stress that must be exerted to maintain constant flow; it determines how well the chocolate will flow into a mold.

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This flow curve is useful in determining the processing objectives in chocolate manufacture. These objectives include assuring a uniform flow rate for enrobing and block making; consistent product; and compliance with industry standards.

For more information and a copy of the application note for measuring chocolate viscosity, contact Brookfield Engineering Laboratories, Inc., 11 Commerce Blvd., Middleboro, MA 02346 (phone 508-946-6200; fax 508-946-6262; www.brookfieldengineering.com) —or circle 312.

USDA Approves Improved Test for DON
Neogen Corp.’s quicker and more sensitive test for deoxynivalenol (DON), a natural toxin in grain, has been approved by USDA’s Grain Inspection, Packers and Stockyards Administration (GIPSA) for official testing in the national grain inspection system. DON is a toxin produced by mold that has been shown to cause vomiting, feed refusal in animals, gastroenteritis, diarrhea, immunosuppression and blood disorders. Even at low levels, the toxin is a concern to the food industry, especially brewers and processed food manufacturers.

 GIPSA authorized the Veratox® for DON 5/5 for determining DON levels in wheat, barley, malted barley, oats, and corn. The new changes to the quantitative test for DON include: a new monoclonal antibody that increases the test’s sensitivity and reproducibility at lower levels; a new liquid conjugate that is ready to use and therefore requires no preparation or delays in running the test; two 5-min incubations; and a new lower limit of detection, with supplied controls now at 0, 0.25, 0.5, 1, and 3 parts per million. For more information, contact Neogen Corp., 620 Lesher Pl., Lansing, MI 48912 (phone 517-372-9200; www.neogen.com) —or circle 313.

PRODUCTS & LITERATURE
Flour and Dry Ingredient Measurement may be done with the InfraPowder Analyzer. The instrument allows for the rapid simultaneous analysis of flour, dairy, powders, spices, ingredients, instant beverages, and other dry ingredients. Sampling configurations include a fast loop configuration through a patented flow cell assembly with sample return to the process. Applications include measuring flour in the milling process for moisture, fat, and ash; cheese powders for fat, moisture, and protein; and instant beverages for moisture, Ace K, and Brix. For more information, contact Bran + Luebbe, Inc., 1025 Busch Pkwy., Buffalo Grove, IL 60089 (phone 847-520-0700; www.branluebbe.com) —or circle 314.

Mercury Sample Preparation System, the Hydra Prep, is designed to automatically digest samples according to operator selectable EPA methods. The system performs all reagent additions and heating steps required to digest a wide variety of sample types. As an added benefit, the system is said to use lower sample and reagent volumes, minimizing the quantity of hazardous waste generated. This series of instruments covers a broad range of applications such as water, soil, fish, tissue, and more. The series consist of cold-vapor atomic-absorption-based and coldvapor atomic-fluorescence-based mercury analyzers. For more information, contact Leeman Labs, Inc., 6 Wentworth Dr., Hudson, NH 03051 (phone 603-886-8400) —or circle 315.

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Moisture Analyzer, the Mark 4, is claimed to be the first moisture analyzer to have a “uni”-balance. That is, the balance mechanism is monolithic and is milled from a solid block of a proprietary alloyed aluminum. There are no fixtures, screws, or incompatible metals in the balance. The design is said to provide fast and accurate moisture results. For more information, contact Omnimark Instrument Corp., 1320 S. Priest Dr., Ste. 104, Tempe, AZ 85281 (phone 480-784-2200; fax 480-784-4738; www.omniwww.com) —or circle 316.

Universal Packaging Tester, the TMI LTL™, is designed for tension, compression, and flexural testing of a variety of materials such as plastics, film, paper, cord, textiles, packaging, rubber, adhesives, and components. It is a compact, single-column bench-top machine with force measurement ranges from 1 N to 2.5 kN and a crosshead travel of 1,000 mm. Interchangeable load cells are available. The integral display gives a readout of peak force (in tension, compression, or flexure), elongation, TEA, and the calculated statistics of mean, standard deviation, and others without the need to connect to a separate PC. This is a major benefit of the instrument over other similar systems on the market. Test parameters may be entered through a control panel in a sequential menu-driven format. For more information, contact Testing Machines, Inc., 2910 Expressway Dr., South, Islandia, NY 11749 (phone 631-439-5400; 800-678-3221; fax 631-439-5420) —or circle 317.

Flat-Surface pH Electrodes are said to be ideal for applications that easily cause coatings to form on the electrode measuring surface, such as viscous fluids, meat, cheese, skin, and other foods. Since the measuring surface is flat, accessibility for cleaning is greater than bulb-style pH electrodes. Additional features of the electrodes include a gel-filled sealed reference, durable epoxy bodies, and high-surface area peripheral reference junctions. For more information, contact Sensorex, Inc., 11751 Markon Dr., Garden Grove, CA 92841 (phone 714-895-4344; fax 714-894-4839; www.sensorex.com) —or circle 318.

Complete GPC/SEC System features triple detector technology and includes columns, standards, pumps, auto or manual injectors, software, and applications support. The instrument employs a concentration detector, viscometer, and light-scattering detector acting in concert, with each detector providing complementary but different information. The integrated detector array consists of three primary detectors: a light-scattering detector which measures molecular weight, a patented four-capillary differential viscometer which determines molecular density and size, and a differential refractometer which measures concentration. The detector array is designed as a module that plugs into the heated oven compartment and is easily removed for maintenance. For more information, contact Viscotek, 15600 W. Hardy Rd., Houston, TX 77060 (phone 281-445-5966; fax 281-931-4336) —or circle 319.

Gas Chromatograph brochure describes the Trace gas chromatograph. The unit is said to be a research-caliber GC at an affordable price. It has a wide selection of modular inlets to provide injection techniques that are best suited for each application. Detector options include flame ionization, thermal conductivity, nitrogen, phosphorus, electron capture, flame photometric, photoionization, and electrolytic conductivity. For more information, contact Thermo Finnigan, 2215 Grand Ave., Austin, TX 78728-3812 (phone 512-251-1555) —or circle 320.

 HACCP Video, called “Inside HACCP: Principles, Practices & Results,” is said to help companies build a more knowledgeable workforce and meet safety standards through a comprehensive overview of HACCP principles. The video opens with a brief introduction of the HACCP food safety system and explores the seven principles. It provides explanations of how HACCP works and places special emphasis on the four principles—monitoring, verification, corrective action, and recordkeeping—in which employees actively participate. For more information, contact Silliker Laboratories Group, Inc., 900 Maple Rd., Homewood, IL 60430 (phone 708-957-7878; fax 708-957-8449; www.silliker.com) —or circle 321.

Dewar Flasks that have been improved to withstand temperatures from –196 to +100°C are now available. The flasks include a finger grip on the bottom and molded-in ribs for easier handling, and a low center of gravity to reduce accidental spills. They also feature a large opening for access and a built-in spout for easier pouring. All the models have high-density polyethylene double-wall construction and CFC-free foamed urethane insulation. Covers are held in place by metal tabs. The flasks have a polyethylene-coated bail-type steel handle for added safety and ease of use. They are available in four capacities: 1, 2, 5, and 10 L. For more information, contact Nalge Nunc International, 75 Panorama Creek Dr., Rochester, NY 14625 (www.nalgenunc.com/dewar) —or circle 322.

by JAMES GIESE
Internet Editor