James Giese

Online instruments to measure various physical and chemical attributes of food can be powerful tools for process and quality control. Control of food processing operations requires timely knowledge of the condition of the material. Physical attributes such as pressure, weight, temperature, and flow rate and chemical attributes such as moisture, fat, and protein must be monitored to control a process and ensure product quality. Various online instruments are available for measuring food attributes. These include refractometers, near-infrared analyzers, and guided microwave spectrometers.


The use of online refractometers to measure constituents of foods is based on the refraction of light. When a ray of electromagnetic radiation strikes a flat surface at an angle, the ray is reflected or refracted. The amount of refraction is a characteristic of every substance and is called the refractive index. In most online refractometers, an LED creates a beam of light which passes through a special optical assembly, focusing the light into a prism in contact with the analyzed liquid. The “critical angle” phenomenon occurs at the interface between the prism and the liquid, where the light beam divides into two parts. One part of the light bends or refracts” as it passes into the product and is absorbed. The other part reflects at the surface as if it were a mirror, following the physical laws of total reflection. The optical image reaching the CCD sensor is therefore divided into two areas: one lighted and the other practically dark. The position of the separation line between the light and dark is a direct function of the refractive index of the liquid. The separation line is detected by an optical sensor. The refractive index can be used to determine component concentration such as the percentage of dissolved solids.

One of the most common uses of refractometers is in the soft drink industry. Refractometers are available which mount directly on the process line to continuously measure inline dissolved CO2 concentration, display the carbonation value, transmit the value in digital and analog mode, and activate alarm relay outputs. Dissolved carbonation is measured using the well-known relationship between saturation pressure, temperature, and carbonation, as defined by Henry’s Law.

Another common type of online food processing instrument is the near-infrared analyzer. Near-infrared reflectance (NIR) is a noncontact technology already in wide use for online analysis of fat, protein, and moisture in the processing of milk powder, snack foods, potato powders, flour starch, and breakfast cereals, among others.

The basic principle of operation of NIR involves light from a quartz halogen lamp being focused into a parallel beam and projected onto a sample. A filter wheel rotating in the optical path contains optical interference filters to transmit narrow bands of infrared energy at specially chosen measurement wavelengths. Wheel rotation speeds of 50 Hz are typical. The pulses of light landing on the product are both scattered and absorbed to some extent. A proportion of the scattered light is focused by a collecting mirror onto a lead sulfide detector, which generates a signal proportional to the reflected intensities at each wavelength. These signals are manipulated using algorithms specific to each application, to give an output proportional to the parameter being measured.

To make an NIR measurement, a product must satisfy three fundamental criteria: absorptivity, selectivity, and sensitivity. A product must be capable of absorbing near infrared energy; the sample must absorb near infrared at energy maxima particular to the component to be measured; and a means of desensitizing to interfering components must exist.

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Raw filter signals are collected from a matrix of samples and used to generate a robust, reliable measurement, which is linearly proportional to the concentration of the component of interest within the test product.

NIR is not an absolute measurement. It needs to be calibrated against a primary reference—usually a laboratory technique. Uncalibrated measurements generated by the algorithm are amplified and offset by applying a gain and zero, so that they correspond with laboratory reference values. Both reflectance and transmission NIR instruments are available. Reflectance instruments scan in the spectral region of 700-2,500 nm, while transmission instruments scan in a much narrower range from 900-1,025 nm.

The dielectric constant and the loss factor of food materials may be used to determine their moisture content. Microwave dielectric analyzers are available to determine both the dielectric constant and the density at the same time, providing density compensation to the moisture measurement.

Guided Microwave Spectrometry (GMS) is a patented system, combining microwave spectral technology with a proprietary waveguide design to provide repeatable composition analysis. Materials ranging from liquids and cloudy slurries to granular flowable solids are routinely investigated using GMS. A GMS system consists of electronic controls and a sensor chamber, which houses a specially designed waveguide. Sensor bodies are available for inline, at line, or laboratory use. The spectrometer in these units transmits broad-frequency, low-power microwaves through the mixture filling the waveguide. This metallic rectangular section in the center of the sensor body creates a defined area for use in measuring the electrical response. Special algorithms are used to analyze the change in these microwaves caused by contact with the process material. For online use, the sensor body is simply a section of pipe. There are no moving parts, optical windows, or filters which require continual replacement or cleaning, protrude into the process stream, or create drift due to coating.

The GMS system detects changes in the key electrical properties—dielectric constant, conductivity, and molecular relaxation time. From these, an analysis of constituent properties is made. Because GMS is a noncontacting technology that measures the entire process stream (instead of only a small segment), the analysis of a representative sample is assured even if the mixture is nonhomogeneous.

Patents this month describe the noninvasive measure of temperature, detection of spongiform encephalopathies, and detection of microorganisms. For a complete description of these patents, go to the U.S. Patent Office Web site at www.uspto.gov/.

Non-invasive measurement of frozen tissue temperature using MRI signal. U.S. patent 6,032,068, filed 2/19/1998, issued 2/29/2000 to B. Daniel et al., assigned to Board of Trustees of the Leland Stanford Junior Univ. Describes a method of using MRI to non-invasively measure the temperature of frozen tissue. The method allows measurement from magnetic resonance signals from the frozen tissue based on spin-spin relaxation time (T2) or based on relative intensity of the magnetic resonance signals. It is possible the method could be used to non-invasively measure temperature in frozen foods.

Detection of transmissible spongiform encephalopathies. U.S. patent 6,033,858, filed 3/30/1998, issued 3/7/2000 to F. Bastian. Describes a method for detecting transmissible spongiform encephalopathies. The method consist of selecting a sample from a subject to determine whether the subject has a transmissible spongiform encephalopathy; and detecting spiroplasma-specific 16S rDNA indicative of transmissible spongiform encephalopathies in the sample. The spiroplasma-specific 16S rDNA is detected by contacting the sample with a pair of oligonucleotide primers and detecting the resulting polymerase chain reaction product, where each of the pair of the oligonucleotide primers is complementary to spiroplasmaspecific 16S rDNA indicative of transmissible spongiform encephalopathies.

Method of detecting organisms in a sample. U.S. patent 5,902,722, filed 12/5/1997, issued 5/11/1999 to J. Di Cesare et al., assigned to The Perkin-Elmer Corp. Describes a method for detecting the presence or absence of an organism in a sample by isolating the organism with an affinity matrix. The organism is then released from the affinity matrix, rupturing the cells of the organism to release total nucleic acid and hydrolyzing or digesting the total nucleic acid to form mononucleotides, or individual free nucleic acid basic and inorganic phosphate to form an analyte solution. This solution is then assayed for the presence of a free nucleic acid base or inorganic phosphate to thereby determine whether the organism was present in the sample.

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Products & Literature
PROGRAMMABLE TEMPERATURE BATHS, the TC Series, are available in three configurations. Temperature ranges as wide as –20 to +200oC are covered, as well as pumping capacities from 11 to 24 L/min and as low as 9 L/min. The series includes accessories for measuring samples directly in a bath and coolers for lower temperatures. For more information, contact Brook-field Engineering Laboratories, Inc., Dept. 154, 11 Commerce Blvd., Middleboro, MA 02346 (phone 508-946-6200)—or circle 368.

FOOD SAMPLING BLENDERS, called BagMixer, are designed to efficiently mix solid food samples in a sterile bag from 5 to 400 mL in less than one min. The blenders may be used by laboratories for the preparation of solid food samples before microbiological analysis. The units blend samples in robust, disposable bags with no contact between sample and machine, which increases hygiene, safety, and sample integrity. The stainless-steel units are equipped with a fully retractable windowed door to allow visual control of the blending process. For more information, contact Interscience, 100 Route de Sainte-Gemme, St. Nom, France, 78860 (phone 33-1-34-6262-61)—or circle 369.

MOISTURE AND FAT in cheese may be measured with the Infralab system. The unit measures moisture and fat in semi-hard and hard cheeses at line. This enables processors to manage yield optimization and increase product shelf life. The system uses infrared reflectance technology and a robust sampling system. For more information, contact NDC Systems, Infrared Engineering, 5314 N. Irwindale Ave., Irwindale, CA 91706 (phone 626-960-3300)—or circle 370.

LIMS NEWSLETTER, called PlusPoints, contains a mixture of technical information, product news, and company news. A guest column lets LIMS experts voice their opinions on a subject of interest. Application-specific articles gives users and prospects insight into how LIMS can be used in laboratory management. For a copy of the newsletter, contact Zumatrix, Inc., 81 Technology Park Dr., Office 125, East Falmouth, MA 02536 (phone 508-457-7911)—or circle 371.

MICROBIAL CONTAMINATION CHECK, called Spotcheck, is a pen-like device which produces a visible color change if a hygiene problem has occurred. The system uses reagents that have two main functions: to amplify trace amounts of adenosine triphosphate (ATP), the universal energy-carrying compound, and to convert ATP into a visible color change. Suitable for use in both large and small food production companies, the device can detect residues and microorganisms on surfaces and process equipment quickly allowing time for remedial action to be taken before food production starts. For more information, contact Celsis, Ltd., Cambridge Science Park, Milton Rd., Cambridge, UK CB4 4FX (phone +44-1223-426008)—or circle 372.

PORTABLE REFRACTOMETERS include 10 different meters that measure Brix sugar in the range of 0 to 82%, some with multiple scales and automatic temperature control. In addition, there are refractometers for measuring honey, salinity, and serum protein. For more information, contact AnalytiChem Corp., 12220 Maycheck Ln., Bowie, MD 20715 (phone 301-352-4075)—or circle 373.

MOISTURE ANALYZER, the Mark 2, is designed for testing cereals, dairy products, food additives, beverages, meat, vegetables, coatings, and slurries. This analyzer features, graphing capabilities, one-button operation, statistics, instrument validation, expanded memory, and internal printer. This unit is said to calculate the final moisture value using test data 'generated for each sample tested. For more information, contact Omnimark Instrument Corp., 1320 S. Priest Drive, Ste. 104, Temple, AZ 85281 (phone 800-835-3211; fax 602-784-4738; www.omniwww.com)— or circle 374.

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EXPERIMENTS SOFTWARE, the Design-Ease® Version 5, is a software package for Windows that may be used to find critical factors that may affect products and processes. This software is a statistical design-of-experiments package for engineers, scientists, and industrial researchers. This version is capable of generating two-level factorial designs and offers rotating 3D plots and interactive 2D graphics. The software package includes free technical and statistical support. For more information, contact Stat-Ease Inc., 2021 E. Hennepin Ave., Ste. 191, Minneapolis, MN 55413 (phone 800-801-7191; fax 612-378-2152; www.statease.com) or circle 375.

BI-METAL THERMOMETER is said to measure from 0 to 200oF. The thermometer comes equipped with a stainless-steel needle that measures five inches in length and comes with a pocket clip, needle protector, neck strap, and needs no batteries. This needle-tip thermometer works best with food having a high liquid content, but can be used to measure the temperature of many foods. For more information, contact All Quality Assurance Products, Inc., 3427 S.W. 42nd Way, Gainesville, FL 32608 (phone 352-335-5161; fax 352-335-4980)—or circle 376.

MICROWAVE ANALYZER, the SMART System5, is designed for automated microwave moisture/solids analysis. The sample is continuously weighed during the drying process. This process is to ensure complete dryness and prevent burning. Utilizing temperature feedback and built-in power control, this system adjusts microwave power to provide reproducible results. The software provides pre-programmed methods and help screens to guide the operator through a test. For more information, contact CEM Corp., P.O. Box 200, Matthews, NC 28106 (phone 704-821-7015; fax 704-821-8710; www.cem.com) —or circle 377.

GAS PURIFIER, the PureFit Modular System®, is said to have high-purity, high-capacity purifiers for removal of water, hydrocarbons, carbon dioxide, and other organics from gases commonly employed in gas chromatography. This all-metal cartridge-model purifier has the ability to provide a purified gas supply to multiple instruments from a single gas source. The systems are available in 1/8-in. and 1/4-in. inlet/outlet connection. For more information, contact J& W Scientific Inc., 91 Blue Ravine Rd., Folsom, CA 95630-4714 (phone 916-985-7888; fax 916-985-1101)—or circle 378.

WHOLE GRAIN ANALYZER, the Infratec® 1241, can be used to measure whole grain such as wheat, oats, triticale, rye, corn, and rice. This unit features ready-to-use calibrations, network capability, built-in multigrain cell, and transferable calibrations from one instrument to another. This analyzer is designed to be used as a stand-alone unit or a network unit. This unit is said to require no sample preparation and is dust and humidity protected. For more information, contact Foss Tecator AB, Box 70, SE-263 21 Höganäs, Sweden (phone +46-42-36-15-00; fax +46-42-34-03-49; www.fossfuture.com) —or circle 379.

PERISTALTIC PUMP, the Masterflex®, is a high-pressure peristaltic pump that is said to transfer fluids at rates between 0.9 and 170 mL/min (depending on tubing selection) at continuous pressure up to 100 psi. This pump contains no gears, valves, seals, or diaphragms to disassemble for cleaning. For more information, contact Cole-Parmer Instrument Co., 625 E. Bunker Crt., Vernon Hills, IL 60061 (phone 800-323-4340; international 847-549-7600; www.coleparmer.com) —or circle 380.

PORTABLE TABLE features two open shelves made of phenolic board with a melamine high-pressure laminate surface which is said to resist stains and corrosion. The shelves are open on all sides for effective equipment transfer from countertop to table. The 19-in.-wide frame is said to fit easily through most doors and wide corridors. The table has a lifetime guarantee, and no assembly is required. For more information, contact Labconco Corp., 8811 Prospect Ave., Kansas City, Missouri 64132-2696 (phone 816-333-8811; fax 816-363-0130; www.labconco.com) —or circle 381.

COLLOID MILLS have been designed to produce fine particle and droplet size in dispersions and emulsions of varying viscosities. The rotor/stator gap and the rotor speed can be controlled during processing for control over final particle/droplet size and size distribution. These colloid mills offer a variety of rotor and stator designs, plus options that allow the mills to be adapted for the cosmetics, food, chemical, and pharmaceutical industries. For more information, contact Bematek, 12 Tozer Rd., Beverly, MA 01915 (phone 877-236-2835; fax 978-922-7801; www.bematek.com) —or circle 382.

PYROLYSIS AUTOSAMPLER, the AS-2500, has been designed to perform thermal desorption and pyrolysis on solid, powder, and viscous liquid samples. This autosampler has a sample capacity of up to 45 samples. Programming is through a hand-held controller or optional software. Temperature programming rates range from 0.01oC/min to 20,000oC/sec, with a maximum temperature of 1300oC. For more information, contact CDS Analytical Inc., P.O. Box 277, Oxford, PA 19363-0277 (phone 610-932-3636; fax 610-932-4158; www.cdsanalytical.com) —or circle 383.

TEMPERATURE RECORDER, the DataSource™, is a multi-use temperature recorder featuring real-time monitoring. This electronic data logger is said to have the ability to record up to 4,000 observations of temperature and is suited for use in process, storage, safety, and quality control applications. Programming and downloading data is accomplished through Windows® based software via interface to an IBM or compatible PC. This model also features an alarm light that will notify the user if pre-set, out-of-safe range temperatures are observed. For more information, contact, Cox Recorders, 69 McAdenville Rd., Belmont, NC 28012 (phone 704-825-8146; fax 704-825-4498; www.cx-en.com/cox.htm) —or circle 384.

VACUUM OVENS, the Heraeus Vacutherm 600, are self-heated ovens that are said to rapidly and gently heat samples that are prone to decomposition. Direct heat transfer from the shelves, each with individual temperature control, allowing temperatures of up to 400oC to be reached. Standard equipment includes digital temperature controller, independent/adjustable temperature limit cut-off, inert gas connection, and an analog pressure display. For more information, contact Kendro Laboratory Products, 31 Pecks Ln., Newtown, CT 06470-2337 (phone 800-522-7746; www.kendro.com) —or circle 385.

Associate Editor

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