Electronic Noses

Electronic nose instruments are based on the fact that flavors, odors, and volatile compounds are recognized mainly through the sense of smell. The volatile and semi-volatile compounds which interact with biological sensors in the nose are responsible for odor. The unique quality and character of many products are found in the chemical volatiles which comprise their odor. The ability to reliably measure and identify quality factors impurities, taints, and adulteration is key for many companies to insure product quality consistency. Sensory panels have been identifying odors for years; however human panels are subject to fatigue, inconsistencies and are not able to compare over long periods of time.

There are two traditional methods for odor control and regulation analysis in the food industry. One method is to use advanced analytical instruments in laboratories. These methods can give very detailed information about the precise contents of the odor. While classical analytical techniques, such as gas chromatography (GC/MS) separate, quantify and identify individual volatile chemicals, they cannot tell if the component has an odor and data is often difficult to correlate with sensory information and is costly to produce. The results from these instruments must be thoroughly analyzed, and much of the information is not relevant. The other traditional method is the use of human test panels. Human sensory evaluation is a very powerful method. However, it has a number of limitations. Human sensory panels are expensive and time consuming. Even the most highly trained human testers are subjective, and illness and other factors can influence their performance. In contrast, the advantages of electronic noses include rapid, real-time detection of volatiles, less preparation time, greater safety, lower costs, and the ability to conduct automated odor measurements.

An electronic nose is composed of a chemical sensing system (such as a sensor array or spectrometer) and a pattern recognition system (artificial neural network). The sensing system can be an array of several different sensing elements (chemical sensors), where each element measures a different property of the sensed chemical, or it can be a single sensing device (spectrometer) that produces an array of measurements for each chemical, or it can be a combination. Each chemical vapor presented to the sensor array produces a signature or pattern characteristic of the vapor. By presenting many different chemicals to the sensor array, a database of signatures is built up. This database of labeled signatures is used to train the pattern recognition system. The goal of this training process is to configure the recognition system to produce unique classifications of each chemical so that an automated identification can be implemented.

Currently, the biggest market for electronic noses is the food industry. Applications of electronic noses in the food industry include quality assessment in food production, inspection of food quality by odor, control of food cooking processes, inspection of fish, monitoring the fermentation process, checking rancidity of cooking oils, verifying if orange juice is natural, monitoring food and beverage odors, grading whiskey, inspection of beverage containers, checking plastic wrap for containment of onion odor, and automated flavor control to name a few. In some instances electronic noses can be used to augment or replace panels of human experts. In other cases, electronic noses can be used to reduce the amount of analytical chemistry that is performed in food production especially when qualitative results will do. Examples in the food industry include: application in product development such as M&M/Mars and their search for improved chemical formulations; use for quality assurance by Anheuser-Busch to do beer testing, the Florida Dept. of Citrus’ purity testing, pulp wash detection, and Frito-Lay in the quality control of potato chips.

Environmental applications of electronic noses include analysis of fuel mixtures, detection of oil leaks, testing ground water for odors, and identification of household odors. Potential applications include identification of toxic wastes, air quality monitoring, and monitoring factory emissions.

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A variety of companies are developing and marketing electronic noses for the food industry:

Low-cost electronic noses that can be carried in the palm of the hand are now becoming commercially available after being developed during the past five years.

Cyrano Sciences (Pasadena, Calif.) will release in the first quarter of 2000 a light-weight, portable electronic nose for use in the field to detect volatile compounds. The device incorporates an easy-to-read graphic LCD with back lighting. Connection ports will enable downloading of data into spread-sheet packages. Rapid response time, combined with one-button operation will provide an effective and accurate measure of the vapors present. Standard, easily replaceable or rechargeable batteries will supply power. Housed in a robust, water-resistant case, the portable electronic nose will be suitable to all environments. The sensors have been shown to respond to a wide range of organic compounds, bacteria and natural products.

Researchers at Cyrano have developed applications of the portable electronic nose technology to provide an objective basis for the subjective descriptors of different coffee aromas, comparing volatile components from essential oils, detecting off-odors in packeging, and for checking quality of medium-grain rice. Researchers at the School of Engineering, University of Warwick in the U.K. (shown in the photo) have used the portable e-nose technology to predict the ripeness of bananas as well as apples. The technique has also been applied to other fruit, such as mangos, avocados, pineapples, and melons, and a variety of vegetables. Their technology has produced general purpose, desktop size, electronic noses. These may be used for checking the ripeness of certain fruits for food suppliers and supermarkets.

Osmetech (Hollis, N.H.) was founded under the name AromaScan in 1994 based on technology developed at the University of Manchester Institute of Science and Technology (UMIST) in the UK. The company’s products are based on its unique conducting-polymer sensor array. Across this array, the user is able to measure dynamically the total headspace of a sample. The Osmetech conducting polymers are produced by the electro-polymerisation of derivatives of polypyrole, polyaniline and polythiophenes which have been modified by attaching different functional groups onto the ring. This ring substitution is unique to Osmetech and enables each element on the array to have a different conductive property. Having multiple sensors allows you to build up many unique patterns. Multiple sensors also increase the resolution of differences between similar samples.

Osmetech’s products include the MultiSampler-SP, which is a complete automated detection system for characterizing the volatile content of a variety of sample types using dynamic headspace sampling, and the Core Sensor Module, which is a high-sensitivity, customizable sampling and analysis module for integration in third-party hardware and sampling processes. Research in the food industry for this company includes contaminant and infestation detection in bulk and in-transit grain, using sensors and physical methods. Osmetech plc support for a joint development by the Silsoe Research Institute, DIAS (the Department of Instrumentation and Analytical Sciences) at UMIST and Cranfield Biotechnology Centre, funded by the UK Ministry for Agriculture, Fisheries and Food.

Perkin-Elmer’s QMB6 Intelligent Chemosensory System is said to provide rapid, cost-effective quality control analysis of odorous compounds. The system is designed for food, cosmetics, pharmaceutical and environmental applications. The Analytical Instruments Division of Perkin-Elmer and HKR Sensorsysteme GmbH have developed an approach to improving the selectivity of chemosensors with the new QMB6 Intelligent Chemosensory System for olfaction detection. The unit offers the combination of automatic headspace sampling with the latest, most advanced intelligent chemosensory technology from HKR. The system is compact, lightweight, and designed for quality control in the food and aroma sector to analyze variety and geographical origins, composition, aroma intensity and degree of freshness. It may also be used to analyze off-odors, contamination, leaching and polymer outgassing in organic materials and pharmaceutical products. Other applications include cosmetics and environmental detection of nuisance smells, harmful substances and filter breakthrough.

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The technology inside the system has been adapted from the example of the olfactory sense in nature. A series of non-selective but different sensor elements provides a signal pattern characteristic of a particular odor or perfume. This signal pattern is evaluated using the methods of pattern recognition. The sensory system consists of a chemosensor array based on quartz crystals. Several sensor elements are integrated on a common quartz substrate. The sensors are coated with different gas-sensitive materials that react differently to the gases and vapors to be analyzed. Six different sensors are built into a temperature-controlled measuring chamber. An uncoated reference structure can be used to compensate for disturbances.

The Alpha MOS ( Hillsborough, N.J.) analytical instrumentation company was set up in 1992 to develop, manufacture and sell Smart Sensing Systems. Alpha MOS offers a variety of electronic nose instruments including the Odorscanner. This instrument has Windows-based software that automatically analyzes up to 96 samples simultaneously with no operator attention required. Features include a programmable sample volume as well as flexible sampling sequences that can be stored and retrieved at any time. Alpha MOS has a new range of electronic noses called the Fox series. The Fox 2000 is designed for routine quality control. It is configured as a 6 sensor array system and can be use specifically designed array for some sample matrixes. An array of 6 sensors is flexible and adaptable to provide selectivity and reproducibility. The configuration is commonly used for the routine analysis of grains, plastic, pulp and paper, meat and dairy products where odor intensity need to be assessed and controlled. The Fox 3000 provides either 12 sensors of same technology or 12 sensors of different type. By providing the flexibility of different sensor types, this unit may be sensitive to a broader range of compounds. The Fox 4000 and FOX 5000 are configured with respectively 18 to 24 sensors and are designed for use in research and development applications.

Nordic Sensor Technologies Inc. (Jersey City, N.J.) has launched the new NST 3310 and 3320 Electronic Nose instruments for odor and quality analysis. The NST 3320 was developed specifically for use in demanding food industry applications and employs a specially designed autosampler that allows food samples to be heated or cooled individually to maintain optimum sample quality and reproducibility. The NST 3310 instrument is designed for process monitoring or coupling to a high-capacity autosampler. These instruments are said to be of particular significance to processing applications in, for instance, the food and drink industry because, for the first time, it enables the direct on-line integration of an electronic nose with little or no preparation of the sample required. The company is also working on a project for developing an electronic nose for milk analysis on the farm. The purpose is to improve and simplify quality control of milk products. The goal is that the milk analysis project will result in a working intelligent sensor system that is suited for on-line quality- and process-control within dairy production.

PATENTS
Patents this month describe various sensors for food quality control. The complete patents are available via the Internet at www.uspto.gov.

Sensor arrays for detecting microorganisms. U.S. patent 6,017,440, filed 12/11/1998, issued 1/25/2000 to N. Lewis and M. Freund, assigned to the Calif. Institute of Technology. Describes a sensor array for detecting a microorganism. The array consists of first and second sensors electrically connected to an electrical measuring apparatus, where the sensors comprise a region of nonconducting organic material and a region of conducting material compositionally that is different than the nonconducting organic material and an electrical path through the regions of nonconducting organic material and the conducting material. A system for identifying microorganisms using the sensor array, a computer and a pattern recognition algorithm, such as a neural net are also described.

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Odor sensor. U.S. patent 5,928,609, filed 7/14/1997, issued 7/27/1999 to T.D. Gibson et al., assigned to Bloodhound Sensors, Ltd. Describes an odor sensor which may be useful for discriminating between the odor of human or other mammalian individuals, and perimidine monomers and polymers which may be used in such a sensor. This sensor allows the user to discriminate between human individuals (or individuals of other mammalian species). A preferred sensor may incorporate display means adapted to provide a display characteristic of the signals from an individual. Such a display may be referred to as an odor profile. In a preferred aspect of the present invention the personnel recognition sensor is adapted to identify a human individual. The sensor may further include a memory adapted to store a library of odor profiles characteristic of particular individuals and means for comparison of the odor profile constituted by the multiplicity of signals from the sensor elements with an odor profile contained in the library. Standard pattern recognition techniques or a neural network may be adapted to retain characteristic features of the multiplicity of signals for incorporation into the library.

Method for conservatively evaluating continuous thermal treatment process for a particulate-containing food product stream. U.S. patent 6,015,231, filed 4/29/1999, issued 1/18/2000 to K. Swartzel and J. Simunovic, assigned to North Carolina State Univ. Describes a method of generating a residence time measurement of a particulate-containing food product while passing the product as a continuous stream through a thermal processing apparatus. The method includes the steps of inserting at least one detectable particle, and preferably many detectable particles, tagged with at least one magnetic implant into the stream at pre-selected intervals; detecting the implant using at least one sensor located at a detection point downstream from a location of the inserting of the detectable particle; determining a time of passage of the detectable particle in the stream using output from the sensor; and generating a residence time measurement for the stream using the time of passage for the detectable particle. The method also includes the use of multiple sensors for detecting the implants. A suitable system and detectable particle for carrying the method are also described.

Reflection measuring device and method for determining quality properties of items, particularly fat-containing items. U.S. patent 6,014,222, filed 9/24/1998, issued 1/11/2000 to C. Borggaard et al., assigned to Slagteriernes Forskningsinstitut. Describes a reflection measuring device for determining quality properties of items. It consists of a measuring head with a housing which is optically open in one side. The housing is designed to be placed on the item requiring measurement of the reflection factor, with the open side turned towards the surface of the item. The system comprises filter elements each positioned adjacent to the other end of one or more of the optical fibers, each permitting passage of near infrared light in a predetermined wavelength range. The device is suitable for the on-line determination of the unsaturated fat content in the fatty tissue of carcasses or meat cuts conveyed on a slaughter or production line. On the basis of the unsaturated fat content, the device determines the consistency type of the fatty tissue (firm, normal or soft fatty tissue).

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Products & Literature
MOISTURE ANALYZERS, the MA50, the MA100, and MMA30, are said to combine speed with flexibility. By using patented microwave technology, the MMA30 can deliver results in less than 50 sec, with a reproducibility of between 0.03 and 0.4% depending on the sample. On the MA50 and MA100, the heating unit can be changed to suit a particular application. For example, the ceramic radiator is ideal for uniform heating and prevents the overheating of specific areas of a sample. Whilst the alternative choice of a halogen lamp unit provides the flexibility of an easy-to-regulate heat source. For more information, contact Sartorius Ltd., Longmead, Blenheim Rd., Epsom, Surrey, KT19 9QN, England (phone 01-372-737-100)—or circle 370.

“FUNDAMENTALS OF WATER ACTIVITY” is the title of an 8-p brochure that provides a compilation of current information on the measurement and definition of water activity. Included in the brochure are sections on how water activity affects quality, safety, and shelf life. Information on water activity’s role in hurdle technology, microbial growth, chemical reactivity, HACCP compliance, is also included. For free copies of the brochure, contact Decagon Devices, Inc., P.O. Box 835, 950 NE Nelson Court, Pullman, WA 99163 (phone 509-332-2756; www.decagon.com/aqualab) —or circle 371.

CHEMICAL ANALYZER, the LISA 200, may be used to determine more than 30 parameters on 150 samples in one hr. The programmable system performs both colorimetric and enzymatic determinations. The analyzer requires as little as 3 μL and can automatically prepare dilutions. It may be used for determination of nitrites, phosphates, sulfates, total nitrogen, cyanides, iron, calcium, manganese, acetic acid, citric acid, malic acid, gluconic acid, glycerol, saccharose, and others. For more information, contact AnalytiChem Corp., 12220 Maycheck Ln., Bowie, MD 20715 (phone 301-352-4075)—or circle 372.

MOISTURE MEASURING SYSTEMS may be used in a variety of industrial process settings. These moisture sensors utilize a high-frequency dielectric shift principle. The sensors detect approximately 6 in into the material and are said to yield greater product representation and more accurate control for improved product quality. The circuitry is protected by a fully potted stainless steel housing with optical face materials to match the environmental demands of the different applications. For more information, contact Arnold USA, Inc., P.O. Box 174, Amery, WI 54001 (phone 715-268-5668)—or circle 373.

BENCHTOP ELECTROCHEMICAL INSTRUMENTS may be used to perform a variety of tests including pH/ORP ISE, conductivity, DO, temperature, and multiparameter configurations. The system organizes bench space through a multifunction box that serves as an electrode stand, storage compartment for cables, and a calibration station complete with beakers, calibration standards, and storage solutions. The meters are available in three functional levels to suit different applications. For more information, contact WTW Measurement Systems, Inc., 3170 Metro Pkwy., Ft. Myers, FL 33916-7597 (phone 800-645-5999 or 941-337-7112)—or circle 374.

LABORATORY HOMOGENIZER may be used for research and development, ingredient optimization, and process simulation in the food industry. The homogenizer has a integrated touch panel that allows the user to select the mixer speed, run time, mix head rotation, program store, and retrieve, pause mode, and print-out mode. It features a reversible mixing head, self-adjusting vortex plate, brushed stainless steel enclosure, and an optional printer for data logging of run time parameters. For more information, contact Chemineer, Inc., 125 Flagship Dr., North Andover, MA 01845 (phone 978-687-0101)—or circle 375.

BACTERIOLOGY PROOFREADING SOFTWARE, BactiSpell, may used with Microsoft Word 97 to enhance the ordinary spelling dictionary with thousands of technical terms. With the software installed, the user can continue to use the familiar spellchecker interface. The software will recognize genus, species, family, and other taxonomical orders as well as thousands of other bacteriology-related terms. The software allows the user to quickly and easily format all taxonomic names in documents according to accepted criteria. Genus and higher order names will be capitalized and italicized. Species names will be italicized and any erroneous capitalization will be removed. The software includes more than 1,500 genus names, more than 5,000 species names, and more than 300 names of other taxonomical orders. It also includes more than 12,000 other entries covering antimicrobials, tests, media, stains, enzymes, proteins, and other biochemicals. It also includes the names of clinically important fungi, yeasts, parasites, and viruses. For more information, contact Microrite, 5019 New Trier Ave., San Jose, CA 95136 (www.microrite.com) —or circle 376.

by JAMES GIESE
Associate Editor

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