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Decagon Devices pawkit Operator's Manual

Portable water activity measurement system
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Portable Water Activity
Measurement System
Operator's Manual
Version 9

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  • Page 1 Portable Water Activity Measurement System Operator’s Manual Version 9...
  • Page 2 Decagon Devices, Inc. 2365 NE Hopkins Court Pullman, W A 99163 (509) 332-5601 fax: (509) 332-5158 www.aqualab.com support@aqualab.com sales@aqualab.com Trademarks AquaLab is a registered trademark of Decagon Devices, Inc. ©2008-2013 Decagon Devices, Inc. All rights reserved...

  • Page 3: Table Of Contents

    Seller’s Liability ..... . 2 2. About the Pawkit ....4 PawKit Specifications .
  • Page 4 Sampling Precautions ....22 Pawkit and Temperature ... . .23 5. Cleaning and Maintenance ..24 Cleaning .

  • Page 5: Introduction

    Customer Support If you ever need assistance with your Pawkit, or if you just have questions, there are several ways to contact us. Our Customer Support and Sales Representatives are available Monday thru Friday, between 7am and 5pm Pacific time.

  • Page 6: About This Manual

    Warranty The Pawkit has a 30-day satisfaction guarantee and a one- year warranty on parts and labor. Note to our Users This manual is written to aid the end user in understanding the basic concepts of water activity, enabling them to use our instrument with confidence.
  • Page 7 Pawkit User Manual 1. Introduction damage or injuries to persons (including death), or to prop- erty or things of whatsoever kind (including, but not with- out limitation, loss of anticipated profits), occasioned by or arising out of the installation, operation, use, misuse, non-...

  • Page 8: About The Pawkit

    Pawkit User Manual 2. About the Pawkit 2. About the Pawkit The Pawkit is designed to be a simple, rapid and portable system for measurement of water activity. It is easy to use, durable, and requires little maintenance. PawKit Specifications Water Activity Range: 0.00 to 1.00...

  • Page 9: How Pawkit Works

    ±0.003 , and measures based upon the chilled-mirror dewpoint method. Contact Decagon for more details. Getting Started Components of your Pawkit System: Your Pawkit should have been shipped to you with the fol- lowing items: • Pawkit main unit •...

  • Page 10: Preparing For Operation

    • AquaLab Cleaning Kit Preparing for Operation To ensure that your Pawkit operates correctly and consis- tently, always place it on a level surface when measuring. This reduces the chance that sample material will spill inside the instrument. To avoid inaccurate readings, place your Pawkit in a location where the temperature remains fairly stable.

  • Page 11: Water Activity Theory

    Pawkit User Manual 3. Water Activity Theory 3. Water Activity Theory Water is a major component of foods, pharmaceuticals, and cosmetics. Water influences the texture, appearance, taste and spoilage of these products. There are two basic types of water analysis: moisture content and water activity.
  • Page 12 Pawkit User Manual 3. Water Activity Theory water activity is of particular importance in determining product quality and safety. Water activity influences color, odor, flavor, texture and shelf-life of many products. Most importantly, it predicts product safety and stability with respect to microbial growth, chemical and biochemical reac- tion rates, and physical properties.

  • Page 13: Temperature Effects

    3. Water Activity Theory in the headspace and measuring the relative humidity of the headspace. In the Pawkit, a sample is placed in a sample cup which is sealed inside a chamber. Inside the sensor block is a capacitive humidity sensor. Changes in the electrical capaci- tance of the polymide layer of the sensor occur as the relative humidity of the chamber changes.

  • Page 14: Water Potential

    Pawkit User Manual 3. Water Activity Theory therefore obtained when the sample is near chamber tem- perature. Water Potential Some additional information may be useful for understand- ing what water activity is and why it is such a useful measure of moisture status in products.
  • Page 15 Pawkit User Manual 3. Water Activity Theory Osmotic Effects Osmotic effects are well known from biology and physical chemistry. Water is diluted when a solute is added. If this diluted water is separated from pure water by a semi-perme- able membrane, water tends to move from the pure water side through the membrane to the side with the added sol- ute.

  • Page 16: Sorption Isotherms

    Pawkit User Manual 3. Water Activity Theory matrix by hydrogen bonding and van der Waal forces. At higher water activity levels, capillary forces and surface tension can also play a role. Sorption Isotherms Relating Water Activity to Moisture Content Changes in moisture content affect both the osmotic and matric binding of water in a product.
  • Page 17 Pawkit User Manual 3. Water Activity Theory and moisture content of potato flakes dried to varying degrees using the standard drying process for those flakes. An isotherm would be constructed using those data, and the moisture content would be inferred using the measured water activity of samples and that isotherm.

  • Page 18: Operation

    Pawkit User Manual 4. Operation 4. Operation Operation of the Pawkit is very simple. Once you have ensured that you have a stable working environment, you are ready to begin sampling. Following is a description of the features and operation of the instrument.

  • Page 19: Sample Preparation And Insertion

    Thermopile Sensor Bottom of Pawkit Sample Preparation and Insertion Your Pawkit system comes with 60 disposable plastic sam- ple cups and 1 stainless steel sample cup. If you run out, additional cups can be purchased from Decagon. Sample Preparation Special care should be taken in preparing the sample in order to get the best readings possible.
  • Page 20 • Fill the cup no more than half-full of the sample. The Pawkit does not require a large sample size to make its reading. As long as the bottom of the cup is covered by the sample and that the sample is representative of the product you wish to measure, you should be able to make accurate readings.

  • Page 21: Sample Placement

    Sample Placement 1. Open the Pawkit by holding the case near the LCD with one hand and pulling down on the plastic sensor cover tab with the other hand. ...
  • Page 22 Ensure the cup is entirely within the recess. Otherwise, the Pawkit will not be level on the bench and the cup will not make a vapor seal with the sensor.

  • Page 23: Taking Measurements

    Pawkit User Manual 4. Operation 3. Once the Pawkit is properly positioned over the sample cup, you are now ready to take readings (see next section titled "Taking Measurements"). 4. To close the instrument, reverse the opening procedure. With one hand holding the case near the LCD pull...
  • Page 24 4. Once the measurement process has been started, the Pawkit will begin to display water activity measurements as well as temperature after 5 seconds, and update the display every second. During this time you will be able to see that it is measuring by looking at the “sunburst”...
  • Page 25 Refer to Chapter 7 for instructions on how to return your Pawkit for repair. NOTE: DO NOT lift or move the instrument during the measurement.

  • Page 26: Turning It Off

    Turning it off To turn off the Pawkit, leave it idle for more than 5 minutes, and it will shut off automatically. If the Pawkit has automati- cally shut itself off, pressing button (I) will wake up the instrument and display the last water activity measurement.

  • Page 27: Pawkit And Temperature

    If your sample is colder than the ambient temperature of the Pawkit, the accuracy of your reading after 5 minutes may be questionable. Wait until the sample’s temperature is similar to that of the Pawkit.

  • Page 28: Cleaning And Maintenance

    5. Cleaning and Maintenance 5. Cleaning and Maintenance Cleaning The accuracy of your Pawkit is dependent on keeping your instrument clean. Dust and sample debris can contaminate the sampling chamber, and must therefore be regularly cleaned out. To clean your instrument, carefully follow the instructions in this chapter.
  • Page 29 Pawkit User Manual 5. Cleaning and Maintenance Here are some tips for keeping your Pawkit clean: • First, watch the instructional DVD included with your cleaning kit to see step-by-step instructions on how to clean your Pawkit. • Use only a soft cotton cloth to clean the LCD. Tissues can scratch the plastic, causing damage.

  • Page 30: Maintenance

    To remove the sensor filter use a knife or needle point to gently pry up the edge of the filter. Your Pawkit was shipped with 3 spare fil- ters and you can order more by contacting Decagon by email at sales@aqualab.com or by phone at 1-509-332-5601.

  • Page 31: Thermopile Sensor Cleaning

    Pawkit User Manual 5. Cleaning and Maintenance NOTE: The capacitance humidity sensor below the filter is extremely fragile! Do not touch it! Thermopile Sensor Cleaning The lens of this sensor must be free of all dirt and lint to be accurate.

  • Page 32: Chamber Cleaning Instructions

    Note: Do NOT reuse Kimwipes. Battery Replacement The Pawkit uses two Lithium-ion battery cells, and they should last for several years. If the battery charge is low, you will see a low-battery indicator icon appear in the lower...
  • Page 33 5. Cleaning and Maintenance 24.6 0.89 To replace the battery, follow these steps: 1. Remove the Pawkit bottom by unscrewing the two screws: Screw Locations 2. Separate the stainless steel top and elastomer (which contains the batteries) from the white plastic bottom.
  • Page 34 (+) battery terminal and the circuit board are in place. 4. Replace the circuit board/plastic bottom in the elasto- mer top. Tighten the two screws to complete the assem- bly of the Pawkit.

  • Page 35: Verification And Calibration

    Pawkit User Manual 6. Verification and Calibration 6. Verification and Calibration As mentioned earlier, the Pawkit takes water activity mea- surements by measuring the change in electrical properties of a special polymer held between two electrodes. Due to the nature of the capacitance humidity sensor, there may be times when you may need to adjust the calibration.

  • Page 36: Steps To Verify Calibration

    Refer to Chapter 5 for shipping instructions. 4. Once the reading is finished, the right button (II) will be active. Button II is only active until the Pawkit shuts...
  • Page 37 0.76 standard. The numbers in the upper right corner indicate the water activity measurement that your Pawkit just read. Press the II button to scroll through the other selections. They are: u76, d76, u25, d25, Sto, u92 and d92. The “u” and “d”...
  • Page 38 0.76 , use the 0.92 standard. If it is normally lower than 0.76 , use the 0.25 standard. If the Pawkit mea- sures the second standard correctly (±0.02), begin test- ing your product. If it does not measure correctly, repeat steps 3-8 for the second standard.
  • Page 39 Pawkit User Manual 6. Verification and Calibration changes in the slope, so the 0.76 verification check is the most important and should be done more frequently. Following is a graphical representation of the calibration routine: Measure 0.76 Standard Adjust 0.76 Calibration if not within ±0.02...

  • Page 40: Support And Repair

    Pawkit User Manual 7. Support and Repair 7. Support and Repair NOTE: If you purchased your Pawkit from one of our inter- national distributors, please contact them. They will be able to provide you with local support and service. When encountering problems with your Pawkit (that can’t be resolved with the help of this manual), please contact Decagon Customer Support at support@aqualab.com, by...

  • Page 41: Repair Costs

    Pawkit User Manual 7. Support and Repair nuts or bubble wrap), ensuring the instrument is suspended in the packing material. Use a box that has at least 2 inches of space between your instrument and each wall of the box.

  • Page 42: Loaner Service

    Decagon has loaner instruments to keep you measuring water activity while your instrument is being serviced. If your Pawkit is still under warranty or you have a service plan with your instrument, there is no charge for the loaner ser- vice.

  • Page 43: Further Reading

    Pawkit User Manual 8. Further Reading 8. Further Reading Water Activity Theory & Measurement Duckworth, R. (1975). Water Relations of Foods. Academic Press, New York. Gomez-Diaz, R. (1992). Water activity in foods: Determi- nation methods. Alimentaria. 29:77-82. Greenspan, L. (1977). Humidity fixed points of binary satu- rated aqueous solutions.

  • Page 44: Food Quality And Safety

    Pawkit User Manual 8. Further Reading Food Quality and Safety Brandt, L. (1996). Bound for success. Controlling water activity gives technologists the edge in developing safe, shelf-stable foods. Food Formulating. Septem- ber:41-48. Franks, F. (1982). Water activity as a measure of biological viability and quality control.

  • Page 45: Water Activity In Foods

    Pawkit User Manual 8. Further Reading Farber, J.M., F. Coates, and E. Daley. (1992). Minimum water activity requirements for the growth of Liste- ria monocytogenes. Letters In Applied Microbiol- ogy. 15:103-105. Garcia de Fernando, G.D., O. Diaz, M. Fernandez, and J.A.
  • Page 46 Pawkit User Manual 8. Further Reading Hand, L. (1994). Controlling water activity and pH in snack sticks. Meat Marketing and Technology. May:55-56. Lee, M.B. and S. Styliadis. (1996). A survey of pH and water activity levels in processed salamis and sausages in Metro Toronto.
  • Page 47 Pawkit User Manual 8. Further Reading Vivier, D., R. Ratomahenina, and P. Galzy. (1994). Charac- teristics of micrococci from the surface of Roque- fort cheese. Journal of Applied Bacteriology. 76:546-552. Fruits and Vegetables Beveridge, T. and S.E. Weintraub. (1995). Effect of blanch- ing pretreatment on color and texture of apple slices at various water activities.
  • Page 48 Pawkit User Manual 8. Further Reading Clawson, A.R. and A.J. Taylor. (1993). Chemical changes during cooking of wheat. Food Chemistry. 47:337- 343. Gómez, R., Fernandez-Salguero J., M.A. Carmona, and D. Sanchez. (1993). Water activity in foods with inter- mediate moisture levels: Bakery and confectionery products: Miscellany.

  • Page 49: Pharmaceuticals/Cosmetics

    Pawkit User Manual 8. Further Reading Sa, M.M. and A.M. Sereno. (1993). Effect of temperature on sorption isotherms and heats of sorption of quince jam. International Journal of Food Science and Technology. 28:241-248. Pharmaceuticals/Cosmetics Ahlneck, C. and G. Zografi. (1990). The molecular basis of moisture effects on the physical and chemical stabil- ity of drugs in the solid state.

  • Page 50: Miscellaneous

    Pawkit User Manual 8. Further Reading Miscellaneous Bell, L.N. and T.P. Labuza. (1992). Compositional influ- ence on the pH of reduced-moisture solutions. Jour- nal of Food Science. 57:732-734. Bell, L.N. and T.P. Labuza. (1994). Influence of the low- moisture state on pH and its implication for reac- tion kinetics.

  • Page 51: Declaration Of Conformity

    Pawkit water activity meter. Model Number: Year of First Manufacture: 2000 This is to certify that the Pawkit water activity meter, manu- factured by Decagon Devices, Inc., a corporation based in Pullman, Washington, USA meets or exceeds the standards for CE compliance as per the Council Directives noted above.
  • Page 52 Pawkit User Manual Declaration of Conformity...
  • Page 53 Index Accuracy 5 AquaLab 5 Batteries 28 replacing 28 Beeper 21, 22 Buttons 19 to begin measurement 20 Calibration 31 Cautions with sampling 22 CE compliance 47 Cleaning 24 sensor filter 26 Closing the chamber 17 Cold samples 23 Contact information 1 Customer service 1 d25 33 d76 33...
  • Page 54 Declaration of Conformity 47 Display 20 Environment for sampling 6 Enzymes and water activity 8 Equilibrium of sample aw and rh 9 of temperature 9 Features 14 Filter sensor 26 Gibbs free energy 10 High temperature 23 Hot samples 23 Humidity related to water activity 5 Inserting samples 17...
  • Page 55 cleaning 25 display 20 Liability seller’s 2 LiCl standards 31 Lids for sample cups 17 Lipids and water activity 8 Liquid phase water 8 Lithium-ion batteries 28 Location for sampling 6 Low battery indicator 28 Maintenance 24, 26 Measurement taking 19 time 21 Molality of calibration standards 31...
  • Page 56 Operation environment 6 Osmotic effects 11 Pawkit accessories 5 features 14 operation 14 Pharmaceuticals 45 Power shutoff 22 Preparation for operation 6 of samples 15 References 39 baked goods and cereals 43 beverages, soups, sauces, preserves 44 dairy products 42...
  • Page 57 Sample insertion 17 Sample cups 6, 15 filling level 16 stainless steel 15 Samples multi-component 15 Seller’s liability 2 Sensor damage 22 Sensor filter cleaning and replacing 26 Sorption isotherms relating water activity to water content 12 Specification 4 Sto 33 Temperature 23 effects on water activity 9 equilibrium 9...
  • Page 58 Vapor phase water 8 Verification 31 steps 32 Verification standards 6, 31 LiCl 31 NaCl 31 Volatiles 22 Warranty 2 Water activity definition 7 effect on food 7, 8 related to microbial growth 8 stability diagram 8 Water content definition 7 vs.

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