Shelf-life Testing

The shelf life of a food is the length of time that a product is acceptable and meets consumer expectations regarding its quality, according to Graf and Saguy, in Food Product Development, From Concept to Marketplace. However, the quality of most foods decreases over time, and there is the natural need to evaluate for how long these products will maintain their commercial value. Shelf-life testing is designed to provide an objective measure of the quality factors that define the food and the point at which failure occurs. This failure is the point at which the food exhibits physical, chemical, microbiological, or sensory characteristics that are unacceptable to the consumer.

Shelf-life testing can be a difficult, daunting, and expensive task. Quality parameters must be monitored periodically for as long as the test is conducted. Such tests normally last at least as long as the required shelf life of the product. In some cases this may be as long as a year or more. Obviously, such a long test does not coincide with a 3-month product development cycle. The amount of sample required can be substantial, as well as the costs of the analysis.

Most shelf-life testing is microbiological or sensory evaluation. With some food products, however, the product developer can analytically determine an index of deterioration throughout the shelf life, that is, a chemical or physical property that corresponds to the sensory quality of the product. Examples include moisture, water activity, peroxide value, headspace oxygen content, redox potential, malonialdehyde, trimethylamine in decomposing fish, water-holding capacity, and loss of ascorbic acid

If it is not possible to establish an analytical test index of shelf life, a variety of techniques have been offered as ways to reduce the testing effort in some fashion. Statistically, experimental designs that minimize the number of samples required may reduce the testing cost while still providing reliable and valid results.

Various accelerated shelf-life testing methods have been developed. The basic ideas behind these types of tests were developed by T. Labuza of the University of Minnesota. With accelerated shelf-life testing, the food is subjected to a controlled environment in which one or more storage conditions, such as temperature, humidity, atmosphere, or light, are maintained at a higher than normal level. This will cause the deterioration rates to increase, resulting in a shorter than normal time for product failure. Since the effects of extrinsic factors on deterioration can be quantified using the Arrhenius equation, the magnitude of the acceleration can be calculated and the true shelf life of the product under normal conditions can be calculated. As described by Labuza, accelerated shelf-life testing requires that the user measure at least one analytical measurement that can be indexed to product quality and then used to mathematically model the deterioration kinetics.

Mathematical models that are based on functions representing the deterioration mechanisms of the product allow the system to be studied and optimized by determining the significance of changes to individual factors used in the model. The storage life of the product can be predicted considering different conditions and failure criteria.

Mathematical modeling is based upon several assumptions. If these assumptions are incorrect, the model no longer stands. Often with models, correction factors are included to account for any conditions which could significantly reduce shelf life.

At the recent 2000 IFT Annual Meeting and Food Expo in Dallas, Tex., some interesting research results on shelf life testing were presented:

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A group of researchers at the Univ. of Conn., Dept. of Nutritional Sciences, and the Food Innovation Center at Oregon State Univ. have explored using digital technology to provide interactive food quality and shelf-life models implemented on the Internet, allowing users access at anytime and anywhere. Their work was aimed at using current technologies to publish “live” demonstration food quality and shelf-life models on the Internet. Their program module was integrated with previous developed models to fully demonstrate the influence of temperature and other parameters on quality and shelf life of various perishable foods. The researchers used two commercial Java-development packages, SmartTable Pro™ and DataVista™ Pro, to convert Excel spreadsheet objectives and chart elements into Java applets. Additional Java codes were created to add communications between charting and spreadsheet objectives, and to bind chart elements to spreadsheet objectives.

The result was an interactive implementation of an Excel spreadsheet that describes quality and shelf life under user-defined storage conditions. Simulation results are shown on the screen immediately, along with a coordinate plot of the spreadsheet table. The program allows users to select storage temperature and time online. Input from client computer is sent to a host server for calculation. Shelf-life data of selected product in the spreadsheet table will change accordingly, upgrading the charts automatically. The program is intended to be used as an instructional aid in demonstrating changes in food quality and shelf life under certain storage conditions. Such a program could also be used for commercial applications.

Also at the 2000 IFT Annual Meeting, A. A. Glueck and C. H. White of the Food Science and Technology Dept. at Mississippi State Univ. have developed a method of evaluating five microbiological tests to correlate them with the predicted shelf life of milk. The ability to rapidly predict potential shelf life of finished milk products is extremely important to dairy processors. Identifying accurate, rapid, and economical tests to detect the presence of contaminants such as psychrotrophs is essential in increasing the keeping quality of fluid milk products. The researchers determined the shelf life of whole chocolate and reduced-fat milk samples from four different dairy plants. Samples were evaluated through preliminary incubation of product at 21°C for 18 hr followed by standard plate count, crystal violet tetrazolium, violet red bile, penicillin, and bioluminescence. Samples were stored at 7°C for seven days. Sensory evaluation was conducted at day 7, day 10, and every other day thereafter until off-flavors resulted. Shelf life ranged from 9.93 to 13.66 days for half-gallon reduced-fat milk and 7.16 to 12.46 days for reduced-fat pint milk samples. Shelf life ranged from 8.60 to 10.63 days for whole chocolate half-gallon and 9.16 to 11.36 days for whole chocolate pints. Out of sixteen product/plant/size combinations, crystal violet tetrazolium had the highest correlation with product shelf life 10 times, bioluminescence had the highest correlation three times, while violet red bile had the highest correlation with shelf life twice and once for penicillin.

PATENTS
Patents this month describe a method for detection of microorganisms and a pump for supercritical fluid extraction. For a complete description of these patents, go to the U.S. Patent Office Web site at www.uspto.gov/.

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Membrane filter agar medium containing two enzyme substrates used for the simultaneousdetection of total coliforms and E. coli. U.S. patent 6,063,590, filed 9/7/1993, issued 5/16/2000 to K.P. Brenner, assigned to The United States of America. Describes an improved method for detection of total coliforms and E. coli. The method consists of placing the target sample in a broth containing an ingredient that will encourage growth and repair of injured coliforms. It also includes at least one agent that suppresses growth of Gram-positive cocci and spore-forming organisms, at least one active agent that will suppress growth of non-coliform Gram-negative bacteria, and at least one chromogen or fluorogen. Both a fluorogen and chromogen are used. Preferred methods include use of filter and/or plates containing the growth-promoting ingredients and the indicators. This method allows simultaneous detection of total coliform bacteria and E. coli. The medium is particularly useful for routine testing of drinking water. The testing of water in certified laboratories for both total coliforms and E. coli at present is usually accomplished using two different tests. Traditional testing of water for drinking and recreation use requires much time. The method allows for testing of other samples that are frequently tested for total coliforms and/or E. coli, including urine samples (human and veterinary), foods, drugs, and pharmaceuticals. Testing of aerosols, soil, and sludge is sometimes required to evaluate the need for control of harmful organisms.

Apparatus and method for supercritical fluid extraction. U.S. patent 6,071,408, filed 5/18/1998, issued 5/6/2000 to R.W. Allington et al., assigned to Isco, Inc. Describes a pump that improves performance in supercritical extraction systems. This specially designed pump includes a cam-driven, single plunger with a cam having a profile that enables the pumping system to avoid destructive reverse torque on the cam, gear train, and drive motor after the cam passes top dead center. The fluid volume leaving the pump is determined by measuring only pressure or other parameters related to flow and movement of the plunger. Measurement of the fluid volume leaving the pump is useful for recording or indicating the flow rate while the pump is operating.

In supercritical fluid extraction, an extraction vessel is held at a temperature above the critical point and is supplied with fluid at a pressure above the critical pressure. Under these conditions, the fluid within the extraction vessel is a supercritical fluid. In one type of apparatus for supercritical extraction, there is a specially constructed extraction vessel within a source of heat and a specially constructed pump for supplying supercritical fluid to the extraction vessel.

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Products & Literature
MINIATURE-SCALE SPRAY CHILLER, the Armfield FT81, is capable of handling high-fat products such as bakery shortening mixes for laboratories or pilot plants. Spray-drying principles for atomization are used, but the process air is cooled instead of heated and the atomizing nozzle is installed in the counter-current position on the chamber to enable longer residence times of up to 18 sec. The unit produces powders comparable to those made in a production-scale plant. The liquid to be spray chilled is atomized by a two-fluid non-clogging nozzle, and the airflow within the chilling chamber is controlled by separate variable-speed inlet and exhaust fans. The operator can also control the temperature and relative humidity in the chamber. An optional data logger allows the major variables such as temperature, pressure, and relative humidity to be logged to a personal computer. For more information, contact Armfield, Ltd., Bridge House, West St., Ringwood, Hampshire, BH24 1DY England (phone 44-(0)-1425-478781; fax 44-(0)-1425-470916; www.armfield.co.uk) —or circle 317.

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SPECTROPHOTOMETER, the Genesys 10, is a new spectrophotometer that features a 5-nm spectral bandwidth. The spectrophotometer is equipped with a xenon lamp, dual detectors, and split beam optics for signal-to-noise ratio. The instrument contains eight built-in software programs. Test parameters and results can be printed on the optional 3-in-wide printer. This spectrophotometer is available in both visible (32–1100nm) and UV-visible (190–1100nm) models. For more information, contact Spectronic Unicam, 820 Linden Ave., Rochester, NY 14625 (phone 716-248-4185; fax 716-248-4014; www.uvvis.com) —or circle 318.

DATA LOGGERS, the HT100 and HT120, may be used to monitor and withstand temperatures from –40 to 125°C. The units feature a waterproof stainless-steel case and are said to be ideal for tracking pasteurization, sterilization process, and cooking. For more information, contact Dickson Co., 930 S. Westwood Ave., Addison, IL 60101-4997 (phone 800-323-2448 or 630-543-3747; fax 630-543-0498; www.dicksonweb.com) —or circle 319.

REVERSIBLE HOMOGENIZER, the Model CJ-4D, may be used for high-speed shearing, dispersion, and emulsification in laboratories. It is said to be the largest laboratory-sized rotor/stator mixer commercially available with a pumping flow rate of 333 L/min. It has operating speeds of 10,000 rpm producing a peripheral velocity upward of 5,000 ft/min. The extremely high shear rates are capable of deagglomerating tightly bound powder aggregates with fine-grain emulsions in the single-micron droplet size. To incorporate solids, a down-mode flow pattern draws floating powders off the top surface and then blasts any settling materials off the bottom of the vessel with a high-velocity flow. After introducing all ingredients, the mixer is reversed to the up mode and run at full speed for the highest shear. Excess surface turbulence is controlled by location of the variable level baffle plate. Finally, the batch can be atmospherically deaerated by reducing the mixer speed and gently pumping air incorporated liquid from the bottom of the batch to the top surface where bubbles can escape. The unit is equipped with a mixer stand, control box, and 0.75-hp motor. For more information, contact Arde Barinco, Inc., 500 Walnut St., Norwood, NJ 07648 (phone 201-784-9880; fax 201-784-9710; www.arde-barinco.com) —or circle 320.

ELECTRONIC OIL TESTER, the Fri-Check® makes it possible to accurately monitor frying oil at all stages of its useful life. The test shows the point to discard the abused deep frying fat or oil. The tester is said to be easy to use and provides data that correlate closely with laboratory analysis methods. The determination of the polar compounds is accepted criteria for monitoring the degradation of frying oils and fats. The principle of operation is simple and based on viscosity of the oil. The tester calculates the “polar materials” content of the frying oil. For more information, contact Fri-Check, E. Deneve, Grote Baan 375, B 2235 Hulshout (phone 321-669-4290; fax 321-669-4291)—or circle 321.

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CONTROLLED STRESS/STRAIN RHEOMETER, the StressTech HR, is designed for research and quality control and couples ultra-low-position resolution, high angular velocity, and a wide torque range with a Windows-based user interface. The software utilizes mouse control and features multitasking, help screens, menus, and files that are transferable to other applications. Transitent (creep) and periodic (dynamic oscillation) testing modes are available. Samples can range from low-viscosity fluids to solid pastes. The instrument comes standard with automatic gap setting and quantitative normal force, allowing the user to enter constant force loading and normal stress measurements. All measuring systems such as cone/plate and plate/plate are supported. Temperature range is –180 to 500°C. For more information, contact ATS RheoSystems, 52 Georgetown Rd., Bordentown, NJ 08505 (phone 609-298-2522; www.atsrheosystems.com) —or circle 322.

MICROWAVE ACCELERATED REACTION SYSTEM, the MARS 5™, is said to provide rapid acid digestion for nutrition labeling, trace metal analysis, and product verification. The system can digest up to 14 samples with a slide-in vessel assembly and snap-in sensor connections. The system is constructed of solid steel, is encased in a protective polymer shell, and features a fluoropolymer-coated cavity and an impact-resistant door. For more information, contact CEM Corp., P.O. Box 200, Matthews, NC 28106-0200 (phone 800-726-3331)—or circle 323.

HYDROGEN SULFIDE MONITORING may be done with a sensor offered by Control Instruments Corp. The sensor is said to be suitable for monitoring applications in wastewater and chemical processing plants. The sensor incorporates a capillary barrier that eliminates the possibility of puncturing problems. An on-board heater protects the sensor and extends its useful operation in subfreezing temperatures. For more information, contact Control Instruments Corp., 25 Law Dr., Fairfield, NJ 07004 (phone 973-575-9114; www.controlinstruments.com) —or circle 324.

TEXTURE ANALYSIS systems offer the flexibility to test food texture as well as food packaging. The systems feature a range of food texture application testing solutions for usage in R&D laboratories, quality control, and process control labs. The systems are said to be ideal for shelf-life studies and quantifying the effects of ingredient changes. In addition to the systems, texture analysis software is available to determine the texture properties for a range of food and food products. For more information, contact Instron Corp., 100 Royall St., Canton, MA 02021 (phone 781-575-5000)—or circle 325.

STERILE MEDIA, the BBL Isolator Pack, is designed for use within isolator systems. The media pack is said to have been performance-validated after exposure to the vaporized hydrogen peroxide atmosphere used during isolator facility decontamination cycles. The multi-wrap packaging is said to prevent exposure to the media to vaporized hydrogen peroxide. The media pack is gamma-irradiated and validated sterile according to AAMI guidelines. For more information, contact BD Biosciences (phone 800-638-8663; outside the U.S. 33-4-7668-3636)—or circle 326.

by JAMES GIESE
Associate Editor