Texture Measurement in Foods
Food texture is a physical property of foods arising from the structural constituents and is evaluated by touch. Textural properties are related to the deformation, disintegration, and the flow of a food under force. They are measured objectively by the functions of time, mass, and distance. The study of texture is a branch of rheology. Rheology is the science dealing with the study of the deformation and flow of matter. Rheology studies both viscosity and texture.
Viscosity can be defined as the internal friction of a fluid or its tendency to resist flow. The distinction between viscosity and texture is simple. Viscosity relates to fluid foods or foods that flow, and texture relates to solid foods.
Although the pure science of rheology can define and compute ideal properties of foods, the technologist is mainly concerned with the process of mastication and how foods are perceived in the mouth. This takes us back to the measurement of texture. While sensory tests and descriptors are highly useful in understanding product rheology, there are problems and costs associated with training and maintaining of sensory panels. As an alternative, instruments for rheological food measurements are straightforward to use and provide consistent and significant data.
Often, instrumental texture measurements are grouped as fundamental methods, imitative methods, or empirical methods.
Fundamental methods are based on the measurement of physical proper ties of the food. These are mechanical properties based on stress-strain relationships. The data can be useful for determining processing characteristics. Imitative methods are designed to simulate the chewing process. These usually involve subjecting the food to controlled compression in a manner which simulates the initial stages of chewing. Such methods often correlate well with sensory data. Empirical methods involve subjecting the food to a force using a device having specific characteristics. The data are usually highly specific to a particular food and are difficult to generalize.
Texture measurements are based on stress-strain relationships or rheological properties. Texture instruments have been classified as measuring force, distance, time, and energy. They may also measure ratios of these variables or measure in multiple units. Force measuring instruments are some of the most commonly used in the food industry. In this type of instrument, the variable is force, while time and distance are constant. A wide variety of instruments are available to assess puncture strength, extrusion, shear, crushing, tensile, torque, and snapping strength.
Stress is a measure of force concentration on a material, i.e., the force per unit area (measured in Newtons). It is a measure of the relative displacement between the particles of a material. Strain is the change in dimensions of a sample caused by the application of a stress.
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Texture instruments have applications in the areas of product development, product substitution, and quality control. Often in the product development process, they support sensory testing. After the product is initially developed, the instrumental measurement of texture can provide a standard for specifications. Another area in which these instruments may be used is in substituting for a current product. Often, developing a product substitute is a back-and-forth process, and texture instruments can help in keeping to a standard. Texture instruments are also often used in quality control situations.
Various instruments are available from several suppliers that address these needs.
Texture Technologies Corp. offers the Stable Micro System of texture instruments. The Stable Micro Systems family of instruments may be used to measure hardness, fracturability, springiness, adhesiveness, spreadability, tensile strength, and more in dough, bread, cookies, cakes, pasta, icings, jellies, dairy products, fruits, vegetables, and other foods. The family of instruments is used in both research and quality assurance testing.
One of the most recent instruments from this group is the TA-XT Plus Texture Analyzer. The instrument has been enhanced with the ability to plug in peripheral instruments to provide multichannel data acquisition. This allows for relevant test equipment to be used in conjunction with other units (with their data simultaneously collected), such as temperature monitors to test dairy products, and humidity monitors to test dry products—crackers and biscuits, for instance. Modifications have been made to maximize the flexibility of the texture analyzer. These include multistage test programming facilities so the user can define individual arm-movement sequences at various speeds and distances. This unique control feature enables the most complex test protocols to be established. As a result, the texture analyzer is no longer limited to fixed library tests. The speed range of the instrument has also been extended. Speed can also change in proportion to the height of the sample, so products can be tested at a constant strain rate. For more information, contact Texture Technologies Corp., 18 Fairview Rd., Scarsdale, NY 10583 (phone 914-472-0531; fax 914-472-0532; www.texturetechnologies.com).
Instron Corp. is a provider of testing equipment designed to evaluate mechanical properties of materials and components. Recently, the company introduced a hand-held mechanical tester, called the In-Spec 2200. The portable testing instrument is designed for testing firmness, texture, and ripeness for a variety of foods. The hand-held tester easily converts between two test modes: “push-pull” and “tension-compression.” In the push-pull mode, the force is reacted against the object itself. In the tension-compression mode, the force is reacted against a built-in crosshead. In both operational modes, the tester applies load or displacement at known, repeatable speeds to ensure consistent testing and results.
This new device is equipped with a color, hand-held Personal Digital Assistant (PDA) that monitors tests, captures results, and connects to networks. With the PDA, data can be downloaded to a PC or network, or uploaded to individual testers to provide instructions and work requirements.
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The tester can be customized with grips, fixtures, and application software to meet unique testing requirements. In both operational modes, the tester applies load or displacement at known, repeatable speeds to ensure consistent testing and results. For more information, contact Instron Corp., 100 Royall St., Canton, MA 02021 (phone 781-828-2500; fax 781-575-5751; www.instron.com).
Food Technology Corp. is a manufacturer of food texture gauges based on the Kramer shear press. The company is offering the newly redesigned TP-6 shear press. It is said to be lighter and quieter than any previous shear press offered by the company. The hydraulic system is capable of up to 3,000 lb of force, for testing very hard products and large sample sizes. The shear press comes with the industry-standard shear-compression test cell as well as a force transducer. The transducers, or “load cells,” are available in force ranges of ±10, 50, 100, 250, 500, 1,000, and 3,000 lbs.
The press offers four testing modes: Manual, “One Bite,” TPA, and multi-step programmable mode, selectable data acquisition rates and filters with >2.5-min test duration at the highest rate; and data display and storage in either metric or English units. The system also offers automatic calculations of integrals, slopes, curvatures, statistics, and Texture Profile Analysis parameters. It also features exportation of test data to other programs and applications. For more information, contact Food Technology Corp., 45921 Maries Rd., Suite 120, Sterling, VA 20166 (phone 703-444-1870; fax 703-444-9860; www.foodtechcorp.com).
C.W. Brabender Instruments, Inc. is a manufacturer of laboratory testing equipment designed for physical testing applications. The company specializes in measuring dough and wheat gluten quality for bread making. A new offering from the company is the Micro Visco Amylo Graph. It evaluates starch or flour samples at a fraction of the standard requirements. Only 5–10 g of sample is needed for an evaluation. Total test time can be reduced by the elevated temperature rate increase (up to 10°C/min). The new instrument follows previous Brabender® models, monitoring and recording actual stock temperature. Correlation software allows use to compare up to 15 different curves. The instrument may be used to measure the gelatinization properties of starch and flour.
Features include variable speed, evaluation of small sample sizes, rapid test results, accelerated temperature rates, real stock temperature measurement, port for liquid addition, and correlation software. For more information, contact C.W. Brabender Instruments Inc., 50 E. Wesley St., South Hackensack, NJ 07606 (phone 201-343-8425; fax 201-343-0608; www.cwbrabender.com).
Brookfield Engineering Laboratories, a leader in viscosity measurement, has recently expanded its product offerings by acquiring the texture products division of CNS Farnell, formerly known as the Stevens line of texture analyzers. Their products include the standardized Stevens LFRA texture Analyzer and the QTS-25 Texture Analyzer. The QTS 25 is a overall texture analysis tool operating at forces up to 25 kg while providing a resolution of 1 G force. The system is said to be versatile and operates in conjunction with a software package permitting the calculation of all Texture Profile Analysis parameters (e.g., hardness, springiness, etc.) as well as a wide range of fundamental calculations, including Young’s modulus. The instrument is available with a wide range of accessories that enable the generation of many different test conditions ranging from back extrusion to force in tension.
According to the supplier, the system may be used for research and development applications environment where large numbers of samples may be assessed and up to ten results at a time cross-compared for trends or patterns. For more information, contact Brookfield Engineering Laboratories, 11 Commerce Blvd., Middleboro, MA 02346 (phone 508-946-6200 or 800-628-8139; fax 508-946-6262; www.brookfieldengineering.com; or for more information on the instruments see the CNS Farnell web site (www.textureanalysis.com).
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PRODUCTS & LITERATURE
Glassware Washers in the Flask-Scrubber® Vantage™ Series are engineered to meet the requirements of the laboratory scientist. Stainless-steel construction is said to be able to withstand heavy use and reduce corrosion and contaminant buildup. Adjustable-cycle programs give the user control in setting the right combination of water temperature, detergent and rinse aid amounts, wash and rinse times, and number of rinses. Memory stores both factory-set and user-set programs for reproducible protocols. The RS-232 port provides a means to document settings and actual washing conditions. The viewing window with light lets the user see each cycle in progress. Temperatures up to 82°C may be programmed for wash and rinse cycles to remove lipids and sanitize glassware. Up to 6 purified water rinses may be programmed to ensure that no water-soluble contaminants are introduced. The forced–air drying system incorporates a 99.97% efficient HEPA filter to remove airborne particulates. For more information, contact Labconco Corp., 8811 Prospect Ave., Kansas City, MO 64132-2696; (phone 800-821-5525; 816-333-8811; fax 816-363-0130.
Laboratory Pump, the PC 3000, may be used for repeat line and science applications. The microprocessor-controlled variable-speed pump is rated for continuous operation. According to the company, flexibility is achieved by allowing the user to set dose, time, and speed variables. The user may also calibrate for fluid viscosity. The microprocessor stores delivery rates for each tube size, but a calibration feature enables the user to store an amended delivery rate for each tube size. The alphanumeric display indicates the value of all adjustable parameters for pump speed (RPM), tube size, flow rate (mL/min or L/min, dose (mL or L), and repeat dose interval time (sec, min, hr). Manual keypad control can be over-ridden by analog signals or computer control via RS232. For more information, contact Clark, 10 Brent Dr., Hudson, MA 01749 (phone 978-568-3400; fax 978-568-0060; e-mail [email protected]).
Relative Humidity Meter, the GrayWolf RH Meter, is said to take advantage of the power of Pocket PC computers. A thin-film capacitive %RH sensor and PT100 temperature sensor are incorporated for fast measurement. The meter displays %RH and temperature, as well as derived moisture readings including dewpoint, wet bulb temperature, specific humidity, absolute humidity, and humidity ratio. The user can also add optional carbon monoxide or carbon dioxide sensors. The application software allows for real-time display of up to 7 simultaneous measurements on a mobile computer, plus instantaneous data-logging and long-term trending. In addition, data file association of text, graphic, audio, photo, CAD/CAM, and calibration notes results in detailed documentation. Changes in sensor tips are available through the tactile screen, and industry/application relevant Word and PDF documents are also included. Additional probes are available for air velocity, toxic gases, and indoor air quality parameters. For more information, contact GrayWolf Sensing Solutions, 12 Cambridge Dr., Trumbull, CT 06851 (phone 203-416-0005; www.WolfSense.com).
Chromogenic/Fluorogenic Medium, BD MI Agar, is a new agar formulated to simultaneously detect total coliforms and Escherichia coli in drinking water by membrane filtration. The agar conforms to the U.S. EPA 1604 approved procedure for monitoring drinking water under the Total Coliform Rule and source water under the Surface Water Treatment Rule. An enhancement to the membrane filtration (MF) test method, the agar increases the analytical quality, while reducing analysis time compared to conventional techniques. Final results are available in 24 hr or less. The benefit for testing facilities is said to be a more efficient, cost-effective, sensitive, and specific tool for the detection of total coliforms and E. coli in drinking water. While the agar is approved for use by certified drinking water laboratories for microbial analysis of potable water, it’s also ideal for a wider range of applications. It may be used to test recreational, surface, or marine water, bottled water, groundwater, well water, treatment plant effluents, water from drinking water distribution lines, drinking water source water and possibly foods. For more information, contact BD Diagnostic Systems, 1 Becton Dr., Franklin Lakes, NJ 07417 (phone 201-847-6800).
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Nutrition Analysis software, called Nutritionist Pro Version 1.3, incorporates a number of new features and an expanded nutrition knowledge base. The new software version comes with an electronic tutorial on CD-ROM, to help new users become familiar with the product’s features and functions more easily. The software is based on the company’s nutrition knowledge base, which contains detailed information on more than 19,000 foods. The company also offers Food Labeling software as a standalone product or as an add-on module to Nutritionist Pro. Food Labeling enables users to create camera-ready Nutrition Facts labels in 17 different formats. In addition, labels may include Nutrient Content Claims, and Hazard Analysis Critical Control Points (HACCP). The labels generated are guaranteed to meet all Food and Drug Administration requirements. For more information, contact First Databank, 1111 Bayhill Dr., San Bruno, CA 94066 (phone 800-633-3453; 650-588-5454; fax 650-588-4003; www.firstdatabank.com).
Food Texture Analyzer, called the Chatillion TAPlus, may be used for both routine testing and more sophisticated analysis. The analyzer can accommodate large samples and accepts a wide range of food texture probes, jigs, and attachments as well as multi-purpose grips for testing food packaging. Using the appropriate test fixture, typical test applications with the instrument include gelatin bloom strength measurement; dough firmness; softness measurement; crumb strength; shelf life of baked goods; cutting forces of bread, meat, and butter; fracture properties of biscuits and confectionery; and compressibility of cooked spaghetti. Tension and compression testing with cycling to load and extension limits extends the testing capabilities. The instrument comes with data analysis and control software. Standard test setups include fatigue cyclic testing for measuring the recovery properties of a sample not expected to rupture and a four-point gel test to measure the four parameters of a gel. Other tests include a single hardness test, single stickiness test for measuring the adhesive force of a sample, a snap strength test, and a stress relaxation test setup for measuring the relaxation of a sample which has been compressed for a length of time. The texture profile analysis setup is designed to measure the hardness, cohesiveness, springiness, gumminess, fracture force, and adhesive force of a food sample. For more information, contact Ametek Test and Calibration Instruments Div., P.O. Box 1982, Largo FL 33779 (phone 727-536-7831; fax 727-539-6882).
Cutting Mill, the SM 2000, is said to be suitable for both experimental and routine sample preparation of soft, medium, tough, elastic, fibrous, and temperature-sensitive materials. The cutting mill is available in two speeds. A complete line of accessories is available, including rotors, hoppers, and sieves to match specific applications. Easy access to the grinding chamber and the foldback hopper make the unit easy to clean. For more information, contact Retsch GmbH & Co., KG 42781 Haan, Germany (phone +9(0)21-29-55-61-0; fax +9(0)21-29-87-02; [email protected]).
Mini Digital Refractometer, the model RF80, measures both % Brix concentration and refractive index. Measurements range from 0 to 45% Brix with 0.1% resolution and accuracy and from 1.333 to 1.4098 nD with 0.0001 resolution and 0.0015 accuracy. The portable compact design features a built-in prism and automatic temperature compensation. The device may also be used to measure temperature from 0 to 40°C with 0.1°C resolution and 0.5°C accuracy. For more information, contact Extech Instruments Corp., 285 Bear Hill Rd., Waltham, MA 02451 (phone 781-890-7440; fax 781-890-7864).
by JAMES GIESE