Water Activity News 2004

2004

Published anuually by DECAGON

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Water Activity and Mars (not the candy bar company!)

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E USED TO believe the moon was made of green cheese. If that was the case we would probably worry about its water activity. Mars, on the other hand, is still a mystery.

The quest to understand Mars and the presence of water in one of its many states of existence is the subject of much conjecture and the object of interplanetary studies by many countries.

Mars

Decagon’s expertise in understanding and measuring water is being put to use in conjunction with NASA and the Jet Propulsion Lab. Decagon will be adding an instrumentation package on the Phoenix 2007 Mars lander to make environmental measurements on the surface of Mars. These measurements will include components used in the Pawkit and Aqualab to measure Relative Humidity (RH) on the surface of Mars.

Besides simply RH, the package will include techniques used with the KD2 Thermal Conductivity instrument. This sensor will measure thermal properties on the surface of Mars.

Decagon continues to pave the way in measuring water, whether in food, green cheese, or on the Martian surface.

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Trade shows 2004 Food Safety Summit Washington D.C. March 17–19, 2004 Pet Food Forum Chicago, Illinois March 29–31, 2004 NEHA 2004 Anchorage, Alaska May 8–12, 2004 IFT Annual Meeting and Food Expo Las Vegas, Nevada July 13–16, 2004 IAFP 2004 Phoenix, Arizona August 8–10, 2004 Fundamentals of Water Activity Seminar October 19, 2004—Philadelphia October 21, 2004—Chicago AAPS Baltimore, MD November 7–11, 2004

INSIDE

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Water Activity & Mars R&D at DECAGON When to calibrate AquaLab Using water activity to control Listeria monocytogenes.

Certifying calibration of AquaLab for HACCP plans.

Temperatures influence on water activity readings.

Water activity regulations for pharmaceuticals.

Book: Water Activity in Foods Want a Piece of the Low-Carb Pie? Sample Preparation

aw Seminars 2004

Sample Preparation NE FACTOR that may affect the water activity (aw) measurement is the sample preparation procedure. Eliminating or reducing this potential variable will yield more consistent and reliable water activity readings.

Reducing variability due to sample preparation will also enable researchers and technicians to better identify other causes of aw change in their products.

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establish procedures to minimize this variable. In order to do this, it is necessary to understand how preparation methods affect different products.

Prominent reasons for product aw fluctuation not due to sample preparation include changes in product formulation, processing methods, or temperature. Such changes may influence product quality, shelf-life, and safety. It is important to understand the effects of sample preparation and

Sample Preparation Testing

Decagon conducted the following research on a diverse range of multi-component food, pharmaceutical, and cosmetic products using three different preparation methods.

To test the effect of sample preparation three different methods were used. The first sample preparation method involved taking the sample from its original packaging and directly placing it into a sample cup. All samples fit into the sample cup with Continued on page 6

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Anthony J. Fontana Jr. Ph.D. Senior Research Scientist Decagon Devices, Inc.

Dear Anthony: How often do I need to calibrate my AquaLab?

D

ECAGON RECOMMENDS all of its water activity instruments be verified before sampling at least once per day, at each shift, or if readings become unstable. Checking the water activity of a standard solution will alert the operator to the possibility of contamination of the unit or shifts in the linear offset from other causes. Verify the performance of your AquaLab with salt standards that have known water activities. Either saturated or unsaturated salt solutions are suitable for verifying instrument performance. Unsaturated salt solutions, at four convenient water activity levels (0.250, 0.500, 0.760, and 0.984), are readily available from Decagon in certified individual pre-packaged vials.

Choose a salt standard with a water activity level that is slightly below the water activity of the sample. Measure the water activity of the salt standard, making sure that the temperature of the standard is within 2°C of the instrument temperature. Make two measurements. The water activity readings should be within ±0.003aw of the given value for your chosen salt standard. If the readings are within ±0.003aw of the known value for the salt standard, prepare a sample cup half full of either Is it time for your food lab to steam-distilled water or a “ketchup” by instrumenting second salt standard above with AquaLab or Pawkit? the water activity of the product to be tested. The second water activity reading should be 1.000 ±0.003aw for water or within ±0.003aw of the known value for the salt standard. This procedure should take no more than 15 to 20 minutes and ensures the highest accuracy for your water activity measurements.

I am a small beef jerky processor and would like to use water activity to control Listeria monocytogenes.

Good news! There is a new FSIS (Food Safety and Inspection Service) Directive 10,240.4 that provides verification procedures for Listeria monocytogenes

aw

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(Lm) control on RTE (Ready-to-eat) products. This FSIS Directive uses a post-lethality treatment (which may also be the antimicrobial agent or process) that reduces or eliminates microorganisms on the product AND (Alternative 1) OR (Alternative 2) an antimicrobial agent or process that suppresses or limits the growth of L. monocytogenes. Water activity is an accepted antimicrobial process that suppresses the growth of Lm. These RTE products are stable with respect to growth of L. monocytogenes by any of the following means: aw < 0.90 aw < 0.92 + refrigerated storage aw < 0.95 + pH < 5.5 pH < 4.5 pH < 5.0 + refrigerated storage How do I certify calibration of AquaLab for my HACCP plan?

Decagon Devices offers an Annual Factory Calibration Service for your AquaLab. This gives you the documented proof for HACCP, ISO, and GMP of the instrument’s compliance with Decagon’s standards for accuracy. The Calibration Service, along with a daily verification of calibration will let you operate your instrument with confidence and ensure the quality and safety of your products.

How does temperature influence water activity readings?

Water activity is temperature dependent. The effect of temperature on the water activity of a food is product-specific. Some products increase water activity with temperature, others decrease aw with increasing temperature, while many high moisture foods have negligible change with temperature. One can therefore not predict even the direction of the change of water activity with temperature, since it depends on how temperature affects the factors that control water activity in the food. Temperature changes water activity due to changes in water binding, dissociation of water, solubility of solutes in water, or the state of the matrix (glassy vs. rubbery).

The temperature coefficient for the water activity of foods range from 0.003 to 0.02aw/°C for highcarbohydrate or high-protein foods. Thus, a 10°C decrease in temperature can cause a lowering in aw ranging from 0.03 to 0.2aw.

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Water Activity News

New Book The importance of temperature control is significant for laboratory comparisons, accelerated shelf-life studies and packaging requirements. Also, temperature may be essential when measuring aw levels near critical values, especially for government regulations or critical control points. Decagon offers a temperature-controlled water activity meter, AquaLab Series 3TE. The Series 3TE lets you set the temperature (15 to 50°C) to easily measure water activities at any constant required temperature.

w Are there water activity regulations for pharmaceuticals like foods?

No, currently there are no water activity regulations for pharmaceutical or cosmetic products.

There is a proposed USP (United States Pharmacopeial) Method <1112> using water activity. USP Method <1112> Microbiological Attributes of Nonsterile Pharmaceutical Products – Application of Water Activity Determination provides guidance on the influence of water activity as it pertains to product formulation susceptibility to microbial contamination. The chapter discusses the potential for improving product preservation by maintaining low water activity. The determination of the water activity of nonsterile pharmaceutical dosage forms aids in the decisions relating to the following: Optimizing product formulations to improve antimicrobial effectiveness of preservative systems.

Reducing the degradation of active pharmaceutical ingredients within product formulations susceptible to chemical hydrolysis.

Reducing the susceptibility of formulations (especially liquids, ointments, lotions, and creams) to microbial contamination.

Providing a tool for the rationale for reducing the frequency of microbial limit testing and screening for objectionable microorganisms for product release and stability testing using methods contained in the general test chapter Microbial Limit Tests <61>

Water Activity in Foods

Fundamentals and Applications Edited by Gustavo B BarbosaCánovas, Anthony J Fontana Jr, Shelly J Schmidt, Theodore P Labuza This one-of-a-kind reference text brings together an international group of food scientists, chemists, and engineers to present a broad but thorough coverage of water activity.

A team of experienced editors designed this book to have lasting value as an introduction to the concept of water activity for neophytes and seasoned professionals in both academia and industry.

Topics have been selected to provide a thorough understanding of the mechanisms by which water activity influences the quality, shelf life, and safety of food products. Concepts in the practical uses and applications of water activity for food formulation, processing, and storage are generously illustrated with practical examples from the food industry that will facilitate later applications by professionals in their own laboratories and production facilities.

512 pages • 0-8138-2408-7 • hb • 2005 • IFT Press

Thermal Conductivity and Thermal Diffusivity KD2 is designed for use for Foods in solids, gels, powders and now liquid samples.

• •Compact •Easy to use •Direct readout Portable

KD2 for foods.

Call today.

DECAGON

800-755-2751 509-332-5158 kd2@decagon.com www.decagon.com/kd2

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Continued from cover

Research and Development

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F THE MANY products in development at Decagon, one of the most exciting is an instrument that generates sample Moisture Sorption Isotherms. The Moisture Sorption Isotherm is the relationship between water activity (aw) and equilibrium moisture content of a sample at a specified temperature. The isotherm for any product is important because it relates the amount of water in a sample to its water activity, which is much more important to know. Currently in its prototype phase, the Isotherm Generator has shown considerable promise as a research instrument whose output is both accurate and reproducible.

Each product has its own unique moisture sorption isotherm due to different interactions (colligative, matric, and capillary) between the water and the solid components at different moisture contents. An increase in aw is almost always accompanied by an increase in the water content, but in a nonlinear fashion. Moisture sorption isotherms are sigmoidal in shape for most foods, although foods that contain large amounts of sugar or small soluble molecules have a J-type isotherm curve shape.

Isotherms are an extremely valuable tool for scientists because they are used to predict potential changes in product stability.

The moisture sorption isotherm of a food is obtained from the equilibrium moisture contents determined at several water activity levels at constant temperature.

Historically, these relationships have been derived by equilibrating samples with saturated salt solutions of known water activities. Samples are equilibrated at constant temperature (isothermal) in sealed Isotherms are hot stuff. chambers with saturated salt solutions at different water activities for up to three weeks. After equilibration is complete, samples are removed from the chamber and the moisture content is determined by some appropriate method (loss-on-drying, moisture balance, microwave balance, or Karl-Fischer). Isotherm curves are constructed using the moisture content and water activity (from the known saturated salt water activity) for each sample. Although this technique has been the standard for many years and yields good sample isotherms, it is very time consuming, and may be hindered by problems like

Water Activity News

molding at high water activities. In the last 20+ years, instruments have become available that produce isotherms much faster and more simply, but these instruments have been extremely expensive and are limited to extremely small sample sizes (around 5 to 10 mg).

The Research and Development group at Decagon is in the process of developing an Isotherm Generator that produces isotherm curves simply, accurately, and at a reasonable cost. Using the AquaLab chilled-mirror dew point sensor and a high-precision balance, the Isotherm Generator produces isotherms on samples that fit in a standard Decagon sample cup (7 to 10 ml or 2 to 10 g, typical). Saturated or dry air is pumped into the sample chamber to increase or decrease the moisture of the sample. After the sample weight changes by a user-defined amount, the aw and weight are measured after equilibrium. The measurement process is fully automated and allows the user to set the flow rate, the maximum/minimum aw values, and several other parameters for the isotherm.

Data from the Isotherm Generator have been promising. Figure 1 shows excellent agreement between isotherms from several different samples of microcrystalline cellulose run in the Isotherm Generator along with the GAB equation fitted with parameters from Bell and Labuza (2000). Work is currently underway to develop a phase II prototype that will control temperature. In addition, the current prototype is being used to test a series of samples where the constants for the GAB equation are published. The expected release for the Isotherm Generator is the beginning of 2006.

Figure 1.

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Want a Piece of the Low-Carb Pie? Avoid Surprises—Read This First!

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OW-CARB DIETS—they’ve gone from fad to phenomenon. Nearly 40 million American dieters say they’re avoiding carbs. And recent research studies showing that low-carb dieters lose more weight will probably send those numbers higher. Is bread dead?

Of course not! Food technologists will always find a way to help dieters eat what they crave without cheating. Since 1999, about 1000 new low-carb products have been introduced in the US market. But transforming a high-carb cheat into a low-carb treat can drastically alter food quality. To make a shelfstable, high-quality product, you need to watch water activity.

Replacing Simple Sugars—A Recipe for Disaster?

If not formulated carefully, low-carb products won’t last like their high-carb siblings. They tend to go stale faster and have problems with mold and microbial growth. Why? Simple sugar binds water very effectively. Dietary fiber, protein, resistant starch, and gums—all typical carb replacers— are much less effective at binding water. So a sugar filled cake will last on the shelf much longer than the low-carb version even if they contain AquaLab can same amount of water. give you the inside Reduce the water “scoop” on water content of the low-carb activity results. cake and you’ll get better shelf-life. But you’ll also probably hear the complaint most associated with low-carb foods: they’re too dry.

To formulate high-carbohydrate foods into lowcarb versions, product developers are using old ingredients such as sugar alcohols and fermentable carbohydrates. Sugar alcohols or polyols (such as sorbitol, mannitol, maltitol, lactitol, xylitol, isomalt, erythritol, or hydrogenated starch hydrolysates) and fermentable starches (such as inulin, polydextrose, or resistant starch) are not digested the same way in the small intestine as regular sugars.

Have Your Low-Carb Cake—And Make it Edible

No question about it—getting the recipe right is tough. It’s not all science. But knowing the water activity gives you a powerful edge. The challenges

inherent in most approaches are the use of “foreign” ingredients that will impart nontypical flavors and textures. Measure water activity and you can hit that perfect point—moist enough to be tasty, but not wet enough to spoil.

Water content measures quantity. It tells you how much water is in your product. Water activity measures quality because it tells you what the water is doing inside the product. Some is bound—tied up chemically within the product. The rest is free. The free water is waiting to be used by passing microbes—but only if there is enough of it. Some need more, some need less, but all need a certain amount of free water. Moisture content tells only how much water there is, not how much is available.

If you measure the water activity of your product, you will know which microbes, molds, and fungi can grow on and in it. By reducing the water activity, you can rule out the growth of whole classes of microbes.

At low water activities, you can preclude the growth of anything at all.

Water Activity—A Precise Tool

You can accurately and routinely measure small changes in water activity. So you can get your cake as moist as possible and still be confident that it will stay fresh and safe on the shelf. Water activity is powerful, because it predicts not just whether microbes and bacteria will grow in the product, but also whether the product will change in quality over time. AquaLab is great in the development lab, because quick readings let you adjust ingredients and processes to get exactly the result you want.

Get the Recipe Right

You know that eighty percent of new food products fail within the first year. So you’re looking for the perfect recipe. A quick, accurate picture of food quality can help—and water activity can give you that picture. It predicts not only freshness and keeping qualities, but also crunchiness, chewiness, lipid oxidation, softness, and many other factors of quality. Want to know more about how water activity can help you get the recipe right? Call Decagon at (800) 755-2751 and ask to speak to a food scientist.

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Continued from page 1

Sample Preparation Applications Note-continued no modification to their original form. The water activity was measured using an AquaLab Series 3 water activity meter. Sample temperature and water activity were recorded. In the second portion of the experiment, new samples were removed from the original packaging and cut or sliced in half before placing into a sample dish. The water activity of each was measured immediately after slicing. In the third experiment, samples were taken from their original packaging and ground for approximately 30 seconds using a mortar and pestle. The samples were immediately transferred to a sample cup, and again, the water activity of each processed sample was measured.

Discussion

The tested products showed varying degrees of influence due to preparation methods. Differences in water activity readings before and after sample cutting or grinding were most pronounced on gelcoated solid dosage forms and the non-coated OTC pharmaceutical product. The four food products tested showed relatively small changes in water activity due to preparation methods.

RECOMMENDATIONS— Representative Sampling

If you are measuring the water activity of consumer products, test them in their final state. If the product isn’t chopped, ground, or sliced before it reaches consumers, avoid doing this to the product before you measure its water activity. Because AquaLab accommodates samples with a volume of less than 10 mL, it is inevitable that some slicing or cutting may be necessary. Keeping this to a minimum will

ensure that the aw of the product you test will be the same as the consumer product. When measuring multi-component foods place a representative amount of each component into the sample cup. In other words, if you’re measuring a product which is filling sandwiched between two cookies, put both parts (cookie and filling) into the sample cup.

Consistency

Establish a sampling procedure with set guidelines.

For example, specify how long your samples should be ground, how they should be handled, and (if you have a temperature-controlled AquaLab) at what temperature they should be measured.

Your Own Testing

Perform preparation tests on your own samples and measure the change in water activity that results.

Use this data to determine the method which produces the most stable results, and incorporate this procedure into your sample preparation practices.

Efficiency

Use the testing data above and your own testing data as a guideline to determine what kind of preparation procedure is right for your products. Eliminate any which you decide are unnecessary.

Sample Exposure

Many products can gain or lose moisture through being exposed to ambient air. In general, exposed products with an aw higher than room humidity will lose moisture, and those with an ERH below room humidity will gain moisture. In order to avoid moisture gain or loss, keep time that the samples are exposed to ambient humidity to a minimum. The sample lids are excellent for short-term storage of samples in the sample cups. Parafilm® the lids on or store samples in hermetically sealed containers to minimize moisture transfer.

Results

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Temperature Dependence of Water Activity

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ecagon Devices, Inc. presented at the Third International Workshop on Water in Foods held in Lausanne, Switzerland on March 29-30, 2004. Dr. Gaylon Campbell, Vice President of Decagon Devices, presented a paper at that conference on the measurement of heat of sorption using a chilled mirror dew point water activity meter. Below is the abstract for the paper or for a copy of the entire paper visit http://www.decagon.com/aqualab/download.html Heat of Sorption Measured using a Chilled Mirror Dew Point Water Activity Meter G. S. Campbell, E. M. Huffaker, and A. J. Fontana The water activity of foods changes with temperature. Typically, increasing temperature increases water activity, but decreasing water activity with increasing temperature has also been observed. The magnitude of the temperature effect typically decreases as the sample water activity increases, and becomes negligible at very high water activity.

If the matrix binding the water is stable with temperature, the effect of temperature on water activity can be predicted using a

ln

( a ) = QR (T1 w2

w1

S

1

1 T2

)

where aw1 and aw2 are water activities at Kelvin temperatures T1 and T2, R is the gas constant (8.3143 J mol-1 K-1 ) and QS is the heat of sorption (J/mol). In general, the value of QS depends on the makeup and the water activity of the sample. If QS is known, then one can predict the temperature dependence of the water activity. As the name implies, QS is also a measure of how tightly water is bound by the sample. A plot of ln aw vs. 1/T should produce a straight line with slope QS/R. Multiplying the slope by R gives the heat of sorption.

We measured heats of adsorption for corn, wheat flour, mustard seed, and powdered milk using an Aqualab Series 3TE with internal temperature control. Sample temperatures ranged from 16 to 40°C, and water activities from 0.1 to 0.75. Heats of sorption ranged from near zero to about 16 kJ/mol. In corn, wheat flour and powdered milk QS decreased rapidly with increasing water activity. In mustard seed QS was near zero and changed little with water activity. In addition to providing measurements from which QS can be computed, these experiments give the temperature dependence of water activity, which is useful for storage studies.

Intermediate benchtop water activity meter—AquaLab LITE

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quaLab LITE incorporates technology from AquaLab, the world’s fastest and most accurate water activity meter, and the ultracompact Pawkit into this midrange instrument. All AquaLab models are supported

by Decagon’s experienced and educated staff.

When you buy an instrument from us, you get unlimited support.

AquaLab LITE uses the same sample cups and standards as AquaLab Series 3 chilled-mirror models and the portable Pawkit water activity meter.

Specifications Range: 0 to 1.0aw Accuracy: ±0.015aw Resolution: ±0.001aw Measurement Time: 5 minutes Sensors: 1) Dielectric humidity sensor 2) Infrared sample temperature Case dimensions: 6 x 7 inches (oval) Weight: 1.5kg (3.3lbs) Power: AC Adaptor

New Instrument

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Water Activity News Dear Customers,

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S ALWAYS, we try to stay on top of all the current issues where water activity can be used to make better products.

In this issue of our newsletter, read all about how water activity can help in the development of “lowcarb” products, certainly an up-to-date topic!

We have a commitment to your success in measuring water activity. If we can assist you in any way, let us know.

Sincerely,

Water Activity Seminars Schedule for 2004 Dates and Venues:

October 19 Philadelphia October 21 Chicago Check our website in early 2005 for spring dates and venues.

What are the Water Activity Seminars all about?

Our one-day short course on Fundamentals of Water Activity will help you understand how the water in your product relates to quality, shelf-life, and safety.

You will learn practical uses and applications of water activity in product formulation, processing, and storage. The concepts will be illustrated with examples from the food industry.

Comments from past Attendees:

Tamsin Campbell Product Manager

©2004 DECAGON Printed in USA

“Excellent presentation overall, particularly the instructor's expertise was second to none!”

—Andrew Kavc, Guernsey Bel “One of the best day-seminars for the money I have attended...Well-organized outline, most information delivered at a level that was understandable and applicable.”

—Julia Linski, Weber Flavors

New dispenser packages.

“Course overall was very good.

Good value learned alot!”

—Mike Duellman, General Mills Register Now! Cost: $179 for one person $159 per person for two or more attendees.

Disposable Sample Cup Specifications

Capacity: 15 ml.

Fill: Minimum sample amount should cover bottom of cup (small gaps OK) with the maximum at half full (7ml).

Material: Low Density Polyethylene (LDPE).

Lids: Allow the short term storage of samples.

Sample cups are purchased in boxes of 500 with discounts for multiple box orders.

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Note: The sample cups are intended to be single-use disposable cups. We cannot recommend that you wash and reuse your sample cups. There is a chance a washed cup may still have residual contamination from the previous sample or may not be completely dry from washing.

http://www.decagon.com/seminar/

DECAGON 950 NE Nelson Court Pullman, Washington 99163 Wanting to get meaningful measurements on your recipes?

Try AquaLab!

800-755-2751 fax 509/332-5158 aqualab@decagon.com www.decagon.com/aqualab

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