Aqua Lab Series 3 Operator's Manual
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Aqua Lab Series 3 Operator's Manual

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Water Activity Meter
Operator's Manual
Version 6
for AquaLab Series 3
Decagon Devices, Inc.

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  • Page 1 Water Activity Meter Operator’s Manual Version 6 for AquaLab Series 3 Decagon Devices, Inc.
  • Page 2 Decagon Devices, Inc. 2365 NE Hopkins Court Pullman WA 99163 (509) 332-2756 fax: (509) 332-5158 www.decagon.com support@decagon.com Trademarks AquaLab is a registered trademark of Decagon Devices, Inc. © 1990-2009 Decagon Devices, Inc.

  • Page 3: Table Of Contents

    AquaLab Table of Contents Contents 1. Introduction ....1 About this Manual ....1 Customer Support .
  • Page 4 AquaLab Table of Contents Changing Languages ....21 Normal Sampling Mode ....22 Continuous Mode .
  • Page 5 AquaLab Table of Contents 12. Support and Repair ... 64 Shipping Directions: ....64 Repair Costs .

  • Page 6: Introduction

    AquaLab 1. Introduction 1. Introduction Welcome to Decagon’s AquaLab Series 3, the industry standard for measuring water activity (a ). AquaLab is the quickest, most accurate, and most reliable instrument available for measuring water activity. Whether you are doing research or working on the production line, AquaLab will suit your needs.

  • Page 7: Warranty

    AquaLab 1. Introduction E-mail support@decagon.com Please include your name, contact information, instru- ment serial number(s), and a description of your problem or question. sales@decagon.com Please include your name, address, phone number, the items you wish to order and a purchase order number. Credit card numbers should always be called in.

  • Page 8: Seller's Liability

    AquaLab 1. Introduction Seller’s Liability Seller warrants new equipment of its own manufacture against defective workmanship and materials for a period of three years from date of receipt of equipment (the results of ordinary wear and tear, neglect, misuse, accident and excessive deterioration due to corrosion from any cause are not to be considered a defect);...

  • Page 9: About Aqualab

    AquaLab 2. About AquaLab 2. About AquaLab AquaLab is the quickest and most accurate instrument available for measuring water activity, giving readings in five minutes or less. Its readings are the most reliable pro- viding ±0.003a accuracy. The instrument is easy to clean and checking calibration is simple.

  • Page 10: Aqualab And Water Activity

    AquaLab 2. About AquaLab on samples with no significant impedance to vapor loss AquaLab is calibrated to a NIST traceable temperature standard. AquaLab and Water Activity Water activity (a ) is a measurement of the energy status of the water in a system. It indicates how tightly water is “bound”, structurally or chemically, within a substance.

  • Page 11: Aqualab And Temperature

    AquaLab and Temperature The AquaLab Series 3 does not control temperature, mak- ing it ideal for the measurement of samples at room tem- perature. However, samples that are not at room...
  • Page 12 AquaLab 2. About AquaLab the temperature difference between your sample and the instrument, you can access a sample equilibration screen at the main menu that can shows the difference in temper- ature between the sample and chamber block (see chpt. 4). If temperature control is desired, Decagon offers a tem- perature-controlled model, the AquaLab 4TE.

  • Page 13: Limitations

    AquaLab 2. About AquaLab 5°C daily, water activity readings will vary by ± 0.01a Such variations in ambient temperatures are uncom- mon. As stated above, this much uncertainty in sample water activity is sometimes acceptable, so there may be no need for temperature control. However, if your lab temperature varies to this degree and you require bet- ter than 0.01a precision, you may want a tempera-...

  • Page 14: Water Activity Theory

    AquaLab 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: water content and water activity. Moisture content The meaning of the term moisture content is familiar to most people.
  • Page 15 AquaLab 3. Water Activity Theory water in a system, and thus is a far better indicator of per- ishability than water content. Figure 1 shows how the rela- tive activity of microorganisms, lipids and enzymes relate to water activity. While other factors, such as nutrient availability and temperature, can affect the relationships, water activity is the best single measure of how water affects these processes.

  • Page 16: Temperature Effects

    AquaLab 3. Water Activity Theory the infrared thermometer measures the sample tempera- ture. From these measurements the relative humidity of the headspace is computed as the ratio of dew point tem- perature saturation vapor pressure to saturation vapor pressure at the sample temperature. When the water activ- ity of the sample and the relative humidity of the air are in equilibrium, the measurement of the headspace humidity gives the water activity of the sample.

  • Page 17: Water Potential

    AquaLab 3. Water Activity Theory perature difference were in error by 1°C, an error of up to 0.06a could result. In order for water activity measure- ments to be accurate to 0.001, temperature difference measurements need to be accurate to 0.017°C. AquaLab’s infrared thermometer measures the difference in tempera- ture between the sample and the block.

  • Page 18: Factors In Determining Water Potential

    AquaLab 3. Water Activity Theory closely related to a thermodynamic property called the wa- ter potential, or chemical potential (m) of water, which is the change in Gibbs free energy (G) hen water concentra- tion changes. Equilibrium occurs in a system when m is the same everywhere in the system.
  • Page 19 AquaLab 3. Water Activity Theory meable membrane, water tends to move from the pure water side through the membrane to the side with the added solute. If sufficient pressure is applied to the solute- water mixture to just stop the flow, this pressure is a mea- sure of the osmotic potential of the solution.

  • Page 20: Sorption Isotherms

    AquaLab 3. Water Activity Theory water activity levels, capillary forces and surface tension can also play a role. Sorption Isotherms Relating Water Activity to Water Content Changes in water content affect both the osmotic and matric binding of water in a product. Thus a relationship exists between the water activity and water content of a product.
  • Page 21 AquaLab 3. Water Activity Theory For example, if one were using the AquaLab to monitor the water content of dried potato flakes, one would mea- sure the water activity and water content of potato flakes dried to varying degrees using the standard drying process for those flakes.

  • Page 22: Getting Started

    AquaLab 4. Getting Started 4. Getting Started Components of your AquaLab Your AquaLab should have been shipped with the follow- ing items: • AquaLab water activity meter • Power cord • RS-232 interface cable • 100 disposable sample cups • Operator’s Manual •...

  • Page 23: Features

    AquaLab 4. Getting Started conditioner and heater vents, open windows, etc. Place the AquaLab in a location where cleanliness can be maintained to prevent contamination of the sample chamber. Features Function Key s LED indicator light Sample drawer Front view of AquaLab Lid thumb-screw RS-232 interface Power cord...

  • Page 24: Preparing Aqualab For Operation

    AquaLab 4. Getting Started Preparing AquaLab for Operation After finding a good location for your AquaLab, plug the power cord into the back of the unit. Before turning it on, turn the knob to the “OPEN/LOAD” position, pull open the sample drawer and remove the empty disposable sam- ple cup.
  • Page 25 AquaLab 4. Getting Started In order to provide the most accurate readings, your AquaLab should ideally be allowed to warm-up for at least 15 minutes after turning it on. This allows the air inside the AquaLab to equilibrate to the temperature of its sur- roundings.

  • Page 26: The Menus

    AquaLab 5. The Menus 5. The Menus The Measurement Screen 0.000 0.0 °C Each time you turn on your AquaLab, the screen above will appear. As mentioned earlier, the water activity and sample temperature are displayed on the screen. On each side of the LCD there are two buttons.

  • Page 27: Normal Sampling Mode

    AquaLab 5. The Menus on-screen user language. If you prefer not to use English, you can change it to one of a variety of other languages: German, French, Spanish, Italian, Swedish, Danish, Nor- wegian, Czech, Portuguese, Japanese, Polish or Finnish. This is done simply by pressing the upper right button of the instrument while the drawer knob is in the OPEN/ LOAD position.

  • Page 28: Continuous Mode

    AquaLab 5. The Menus Continuous Mode Continuous mode reads your sample continuously until you turn the knob to the OPEN/LOAD position. It will read the sample, display the water activity and sample tem- perature, then begin another read cycle without turning the knob.

  • Page 29: System Configuration

    AquaLab 5. The Menus knob is in the OPEN/LOAD position. The following screen will appear: Ts = 23.1 Ts - Tb = 0.125 This screen shows the temperature difference between the sample (Ts) and the chamber block (Tb), allowing you to quickly check if the sample is too hot, which may cause condensation inside the chamber.
  • Page 30 AquaLab 5. The Menus Beeper Beeper Linear offset menu Icon Mode indicator (continuous shown) System configuration menu Completion Notification When you are sampling, the AquaLab has two ways of notifying you that the water activity reading is complete: an audible alarm and a flashing green LED, located on the left front corner of the AquaLab’s case.
  • Page 31 AquaLab 5. The Menus The audible alarm can be turned off completely, it can beep momentarily when the sample is finished and then stop, or it can beep continuously until the knob is turned to the OPEN/LOAD position. EXIT You may press the EXIT button (the lower left button) to exit back to the main measurement screen at any time.

  • Page 32: Cleaning And Maintenance

    AquaLab 6. Cleaning and Maintenance 6. Cleaning and Maintenance Keeping your AquaLab clean is vital to maintaining the accuracy of your instrument. Dust and sampling debris can contaminate the sampling chamber and must there- fore be regularly cleaned out. To clean your instrument, carefully follow these instructions and refer to the labeled diagram below.

  • Page 33: Cleaning The Block And Sensors

    AquaLab 6. Cleaning and Maintenance absorb/release water during verification, calibration, and/ or sample testing. For a smooth and even dew formation, it requires the mirror to be perfectly clean. If there are any contaminants (e.g. fingerprints) on the mirror, the dew will form unevenly and thus affect the accuracy of the reading.

  • Page 34: Cleaning Procedure

    Turn the block over to expose the chamber cavity as shown in the illustration at the beginning of this chapter. NOTE for Volatiles Block: If cleaning an AquaLab Series 3 Vol- atiles Block, follow the cleaning procedures listed below being espe- cially careful not to get cleaning solution or alcohol on the capacitance sensor filter.
  • Page 35 AquaLab 6. Cleaning and Maintenance plastic rod (spatula) and moisten it with isopropyl alcohol or Decagon Cleaning Solution. Note: Do NOT dip a used Kimwipe into your container of IPA or cleaning solution (the IPA or cleaning solution will become contaminated). c.
  • Page 36 AquaLab 6. Cleaning and Maintenance d. DRY--Repeat steps a-b using new, dry Kimwipes to help remove any moisture remaining from the cleaning. e. Visually inspect the mirror for cleanliness. Re-clean if necessary. 3. Clean the Thermopile and Optical Sensor a. Wrap a new Kimwipe around the end of the thin plas- tic rod (spatula) and moisten it with isopropyl alcohol or Decagon Cleaning Solution.

  • Page 37: Checking Calibration

    AquaLab 6. Cleaning and Maintenance Checking Calibration After you have cleaned the chamber and other parts of your AquaLab, it is important to check the instrument’s performance in order to correct for any linear offset that may have occurred during the cleaning process. Before you check the instrument we recommend that you run a sample of the activated charcoal pellets provided in your AquaLab cleaning kit.

  • Page 38: Verification And Calibration

    AquaLab 7. Verification and Calibration 7. Verification and Calibration It is important to verify AquaLab’s water activity calibra- tion against known standards to guarantee optimal perfor- mance and accuracy. Decagon recommends verification daily, once per shift, or before each use (if used infre- quently).
  • Page 39 AquaLab 7. Verification and Calibration that were sent with your initial shipment are very accurate and readily available from Decagon. Using calibration standards to verify accuracy can greatly reduce preparation errors. For these reasons, we recommend using standards available through Decagon for the most accurate verifica- tion of your AquaLab’s performance.

  • Page 40: Calibration

    AquaLab 7. Verification and Calibration pour the contents into an AquaLab sample cup. If for some reason you cannot obtain Decagon’s calibration standards and need to make a saturated salt solution for verification, refer to Appendix A. Calibration When to Verify for Linear Offset Linear offset should be checked against two known cali- bration standards either daily, once per shift or before each use.
  • Page 41 AquaLab 7. Verification and Calibration 2. Empty a vial of the chosen calibration standard into a sample cup and place it in the AquaLab’s sample drawer. Make sure that your standard is as close to the instrument temperature as possible. Note: Make sure the rim of the sample cup is clean.
  • Page 42 AquaLab 7. Verification and Calibration 7. If either one of the verifications is not correct, it is probably due to contamination of the sensor chamber. For cleaning instructions, see Chapter 6. After clean- ing, repeat verification from step two. 8. If you are consistently getting readings outside the water activity of your first calibration standard by more than ±0.003a , a linear offset has probably...
  • Page 43 AquaLab 7. Verification and Calibration 3. Empty the whole vial of a calibration standard into a sample cup. We recommend using the 6.0M NaCl (0.76a ). Do not adjust for the offset using distilled water. Ensure the rim and outside of the cup are clean.
  • Page 44 AquaLab 7. Verification and Calibration 6. Adjust the water activity value to its proper value for the particular calibration standard you are measuring by pressing the up or down buttons until the correct value is displayed. When the value is correct, press the Exit button to store this new value.
  • Page 45 AquaLab 7. Verification and Calibration This flowchart is a graphical representation of the directions given above for checking for linear offset.

  • Page 46: Sample Preparation

    AquaLab 8. Sample Preparation 8. Sample Preparation Your AquaLab will continually provide accurate water activity measurements as long as its internal sensors are not contaminated by improperly-prepared samples. Care- ful preparation and loading of samples will lengthen time between cleanings and will help you avoid cleaning and downtime.
  • Page 47 AquaLab 8. Sample Preparation For example, raisins only need to be placed in the cup and not flattened to cover the bottom. A larger sample surface area increases instrument efficiency by provid- ing more stable infrared sample temperatures. It also speeds up the reading by shortening the time needed to reach vapor equilibrium.

  • Page 48: Samples Needing Special Preparation

    AquaLab 8. Sample Preparation 5. If a sample will be read at some other time, put the sample cup’s disposable lid on the cup to restrict water transfer. For long-term storage, seal the lid by placing tape or Parafilm completely around the cup/lid junction.
  • Page 49 AquaLab 8. Sample Preparation that something is wrong with your instrument; it simply means that your particular sample takes longer than most to equilibrate water with its outside environment. To reduce the time needed to take a water activity reading for coated or dried samples, one thing you can do is crush, slice, or grind the sample before putting it in the sample cup.
  • Page 50 AquaLab 8. Sample Preparation reach an accurate measurement of water activity and noth- ing can be done to decrease the reading times of these types of samples. For faster reading, it is important to have the water activity of the chamber at or below the water activity of these type of samples.

  • Page 51: Low Water Activity

    Samples that have a water activity of less than about 0.03 cannot be accurately measured with the normal AquaLab Series 3 model. Samples with such low water activity val- ues are rare. When a sample’s water activity value is below...
  • Page 52 AquaLab 8. Sample Preparation to ambient temperature before a fast, accurate reading can be made. Rapid changes in temperature over short periods of time will cause the water activity readings to rise or fall until the temperature stabilizes. When the temperature sta- bilizes within one or two degrees of the chamber tempera- ture, you can proceed with normal measurements.

  • Page 53: Taking A Reading

    AquaLab 9. Taking a Reading 9. Taking a Reading Measurement Steps Once you have prepared your sample, you are ready to take readings. The process is simple: 1. Turn the sample drawer knob to the OPEN/LOAD position and pull the drawer open. 2.

  • Page 54: How Aqualab Takes Readings

    AquaLab 9. Taking a Reading may vary depending on temperature differences between the chamber and your sample, and other properties of your sample. Note: Samples that have a large difference in water activity from previous samples may need extra time to reach equilibrium, since some of the previous sample’s atmosphere stays in the chamber after measurement.
  • Page 55 AquaLab 9. Taking a Reading • Take special care not to move the sample drawer too quickly when loading or unloading liquid samples, in order to avoid spilling. • If a sample has a temperature that is four degrees higher (or more) than the AquaLab’s chamber, the instrument will display a message (below) sample too hot alerting you to cool the sample before reading.
  • Page 56 AquaLab 9. Taking a Reading that the mirror has become too dirty to give accu- rate measurements, and you need to clean the mirror and chamber before continuing to sample. For more details about this symbol, please refer to Chapter 11. For cleaning instructions, refer to Chapter 6.

  • Page 57: Computer Interface

    AquaLab 10. Computer Interface 10. Computer Interface Your AquaLab was shipped to you with a standard RS-232 interface cable. Using this, you can use your computer’s terminal program to send water activity data to your com- puter for further analysis and storage. AquaLink Software An optional program that is available for use with your AquaLab is AquaLink.

  • Page 58: Using Windows Hyperterminal

    AquaLab 10. Computer Interface AquaLink screen Using Windows Hyperterminal To use Hyperterminal with your AquaLab, follow these steps: 1. Press the Start button and select Programs > Accesso- ries > Hyperterminal and click on the Hyperterminal icon. 2. At the prompt, choose a name for this program (AquaLab is a good one) and choose an arbitrary icon above to represent it.

  • Page 59: Troubleshooting

    AquaLab 11. Troubleshooting 11. Troubleshooting AquaLab is a high performance instrument, designed to have low maintenance and few problems if used with care. Unfortunately, sometimes even the best operators using the best instruments encounter technical difficulties. Below is quick reference guide that will direct you to detailed solutions of some problems that may occur.
  • Page 60 AquaLab 11. Troubleshooting Troubleshooting Quick Guide (continued) If this problem occurs: Refer to: Screen displays “a >1.0” ......... Problem #6 Verification not correct ........Problem #7 Triangle appears in upper right corner.... Problem #8 Screen displays “Block failure” ......Problem #9 turning on AquaLab PROBLEM #1: AquaLab won’t turn on.
  • Page 61 AquaLab 11. Troubleshooting Caution: Do not use any other kind of fuse or you will risk damage to your instrument as well as void your warranty c. Replace the fuse-holder and push it into the fuse- well until the release tab snaps in place. d.
  • Page 62 AquaLab 11. Troubleshooting dense on the surface of the chilled mirror and alter readings. Please refer to the volatiles section in Chap- ter 8 for hints on reducing difficulties with measuring samples with propylene glycol. If you have further questions regarding the measurement of volatiles con- tact Decagon.
  • Page 63 AquaLab 11. Troubleshooting PROBLEM #4: Message on screen displays the following: sample too hot SOLUTION: 1) Your sample’s temperature is too high for the instrument to equilibrate with it in a reasonable amount of time. The instrument and sample need to be in temperature equilibrium before accurate samples can be made.
  • Page 64 AquaLab 11. Troubleshooting this message will come up. Essentially, it means that there is not enough sample moisture to condense on the mirror and provide a reading. 2) The mirror may be dirty. Try cleaning the mirror and chamber and measuring the sample again. PROBLEM #6: Message on screen displays “a >...
  • Page 65 AquaLab 11. Troubleshooting PROBLEM #8: A small triangle appears in the upper right corner after sampling: 0.853 24.7°C SOLUTION: 1) The mirror needs to be cleaned, along with the rest of the sample chamber, or a volatile contaminant is interfering with the dewpoint determination. This tri- angle is a mirror performance indicator.
  • Page 66 AquaLab 11. Troubleshooting PROBLEM #9: The following screen comes up after turning on the machine: block failure SOLUTIONS: 1) The block is not plugged in to the motherboard. Open the case and check to make sure that the small ribbon cable that connects the block to the mother- board is snapped and locked in place.

  • Page 67: Component Performance Screen

    AquaLab 11. Troubleshooting Component Performance Screen If, after cleaning your instrument and reading the other troubleshooting hints, you have reason to believe that one of the components of your AquaLab may be causing mea- surement error, you can access a screen that will display values for component performance.
  • Page 68 AquaLab 11. Troubleshooting voltage, in units of millivolts. This value should normally be between 400 and 2400mV, and should be steady. You can’t change anything in this screen, but it is here to give you an indication of the component performance. If you notice that any of these values are not what they should be, contact Decagon for further instruction.

  • Page 69: Support And Repair

    AquaLab 12. Support and Repair 12. Support and Repair NOTE: If you purchased your AquaLab from one of our interna- tional distributors, please contact them. They will be able to provide you with local support and service. When encountering problems with your AquaLab (that can’t be resolved with the help of this manual), please con- tact Decagon Customer Support at support@decagon.com, 800-755-2751 (US and Canada), 509-332-2756 (Interna-...
  • Page 70 AquaLab 12. Support and Repair 2. Place an empty sample cup in the sample drawer to help protect it from damage during shipping. 3. Place the AquaLab in a plastic bag to avoid disfiguring marks from the packaging. 4. Don’t ship the power cord or serial cable. 5.

  • Page 71: Repair Costs

    AquaLab 12. Support and Repair Repair Costs Manufacturer’s defects and instruments within the three- year warranty will be repaired at no charge. Non-warranty repair charges for parts, labor and shipping will be billed to you. An extra fee may be charged for rush work. Decagon will provide an estimated repair cost, if requested.

  • Page 72: Further Reading

    AquaLab 13. Further Reading 13. Further Reading Water Activity Theory & Measurement Bousquet-Ricard, M, G. Qualyle, T. Pharm, and J.C. Chef- tel. (1980). Comparative study of three methods of deter- mining water activity in intermediate moisture foods. Lebensmittel-Wissenschaftund-Technologie.13:169-173. Chirife, J., G. Favetto, C. Ferro-Fontan, and S. Resnik. (1983).
  • Page 73 AquaLab 13. Further Reading Karmas, E. (1981). Measurement of moisture content. Cereal Foods World. 26(7):332-334. Kitic, D., D.C. Pereira-Jardim, G. Favetto, S.L. Resnik, and J. Chirife. (1986). Theoretical prediction of the water activ- ity of standard saturated salt solutions at various tempera- tures.
  • Page 74 AquaLab 13. Further Reading Roa, V. and M.S. Tapia de Daza. (1991). Evaluation of water activity measurements with a dew point electronic humidity meter. Lebensmittel-Wissenschaft und-Technol- ogie. 24(3):208-213. Roos, K.D. (1975). Estimation of water activity in interme- diate moisture foods. Food Technology. 29:26-30. Scott, V.N.
  • Page 75 AquaLab 13. Further Reading Troller, J.A. and J.H.B. Christian. (1978). Water Activity and Food. Academic Press, New York. Troller, J.A. and V.N. Scott. (1992). Measurement of water activity (a ) and acidity. In: Compendium of Methods for the Microbiological Examination of Foods. Vanderzant, C. and D.F.

  • Page 76: Food Quality And Safety

    AquaLab 13. Further Reading (1994). Prediction of water activity in food systems: A computer program for predicting water activity in multi- component foods. Revista Espanola De Ciencia Y Tecno- logia De Alimentos. 34:427-440. Vos, P.T. and T.P. Labuza. (1974). Technique for measure- ments of water activity in the high a range.
  • Page 77 AquaLab 13. Further Reading in foods. Critical Reviews in Food Science and Nutrition. 36(5):465-513. Franks, F. (1982). Water activity as a measure of biological viability and quality control. Cereal Foods World. 27(9):403-407. Franks, F. (1991). Water activity: a credible measure of food safety and quality? Trends in Food Science and Tech- nology.

  • Page 78: Water Activity And Microbiology

    AquaLab 13. Further Reading food polymer science: Implications of state on arrhenius and WLF models in predicting shelf life. Journal of Food Engineering. 22:271-289. Rockland, L.B. and G.F. Stewart. (1981). Water Activity: Influences on Food Quality. Academic Press, New York. Rockland, L.B.
  • Page 79 AquaLab 13. Further Reading Garcia de Fernando, G.D., O. Diaz, M. Fernandez, and J.A. Ordonez. (1992). Changes in water activity of selected solid cul- ture media throughout incubation. Food Microbiology. 9:77-82. Gibson, A.M., J. Baranyi, J.I. Pitt, M.J. Eyles, and T.A. Roberts.
  • Page 80 AquaLab 13. Further Reading Kuntz, L.A. (1992). Keeping microorganisms in control. Food Product Design. August:44-51. Li, K.Y. and J.A. Torres. (1993). Water activity relationships for selected mesophiles and psychrotrophs at refrigeration temperature. Journal of Food Protection. 56:612-615. Marauska, M., A. Vigants, A. Klincare, D. Upite, E. Kaminska, and M.
  • Page 81 AquaLab 13. Further Reading Petersson, S. and J. Schnuerer. (1995). Biocontrol of mold growth in high-moisture wheat stored under airtight con- ditions by Pichia anomala, Pichia guilliermondii, and Sac- charomyces cerevisiae. Applied and Environmental Microbiology. 61:1027-1032. Pitt, J.I. and B.F. Miscamble. (1995). Water relations of Aspergillus flavus and closely related species.

  • Page 82: Water Activity In Foods

    AquaLab 13. Further Reading Tokuoka, K. and T. Ishitani. (1991). Minimum water activ- ities for the growth of yeasts isolated from high-sugar foods. Journal of General and Applied Microbiology. 37:111-119. Ucar, F. and I. Guneri. (1996). The effect of water activity ), pH and temperature on the growth of osmophilic yeasts.
  • Page 83 AquaLab 13. Further Reading Clavero, M.R.S. and L.R. Beuchat. (1996). Survival of Escherichia coli O157:H7 in broth and processed salami as influenced by pH, water activity, and temperature and suitability of media for its recovery. Applied and Environ- mental Microbiology. 62:2735-2740. Duffy, L.L., P.B.
  • Page 84 AquaLab 13. Further Reading Luecke, F.K. (1994). Fermented meat products. Food Research International. 27:299-307. Minegishi, Y., Y. Tsukamasa, K. Miake, T. Shimasaki, C. Imai, M. Sugiyama, and H. Shinano. (1995). Water activity and microflora in commercial vacuum-packed smoked salmons. Journal of the Food Hygienic Society of Japan. 36:442-446.
  • Page 85 AquaLab 13. Further Reading Dairy Products Fresno, J.M., M.E. Tornadijo, J. Carballo, P.J. Gonzalez, and A. Bernardo. (1996). Characterization and biochemi- cal changes during the ripening of a Spanish craft goat’s milk cheese (Armada variety). Food Chemistry. 55:225- 230. Hong, Y.H. (1991). Physical and chemical properties of the process cheese on the domestic market.
  • Page 86 AquaLab 13. Further Reading Vivier, D., M. Rivemale, J.P. Reverbel, R. Ratomahenina, and P. Galzy. (1994). Study of the growth of yeasts from feta cheese. International Journal of Food Microbiology. 22:207-215. Vivier, D., R. Ratomahenina, and P. Galzy. (1994). Charac- teristics of micrococci from the surface of Roquefort cheese.
  • Page 87 AquaLab 13. Further Reading Kiranoudis, C.T., Z.B. Maroulis, E. Tsami, and K.D. Mari- nos. (1993). Equilibrium moisture content and heat of desorption of some vegetables. Journal of Food Engineer- ing. 20:55-74. Makower, B. and G.L. Dehority. (1943). Equilibrium mois- ture content of dehydrated vegetables. Industrial and Engineering Chemistry.
  • Page 88 AquaLab 13. Further Reading Zeb, A., R. Khan, A. Khan, M. Saeed, and S.A. Manan. (1994). Influence of crystalline sucrose and chemical preser- vatives on the water activity and shelf stability of intermediate banana chips. Sarhad Journal of Agriculture. 10:721-726. Zhang, X.W., X.
  • Page 89 AquaLab 13. Further Reading Harris, M. and M. Peleg. (1996). Patterns of textural changes in brittle cellular cereal foods caused by moisture sorption. Cereal Chemistry. 73:225-231. Michniewicz, J., C.G. Biliaderis, and W. Bushuk. (1992). Effect of added pentosans on some properties of wheat bread.
  • Page 90 AquaLab 13. Further Reading lar crunchy cereal foods at various water activity levels. Journal of the Science of Food and Agriculture. 70:347-354. Weegels, P.L., J.A. Verhoek, A.M.G. de Groot, and R.J. Hamer. (1994). Effects of gluten of heating at different moisture contents: I.

  • Page 91: Pharmaceuticals/Cosmetics

    AquaLab 13. Further Reading Kusumegi, K., T. Takahashi, and M. Miyagi. (1996). Effects of addition of sodium citrate on the pasteurizing conditions in “Tuyu”, Japanese noodle soup. Journal of the Japanese Society for Food Science and Technology. 43:740-747. Sa, M.M. and A.M. Sereno. (1993). Effect of temperature on sorption isotherms and heats of sorption of quince jam.
  • Page 92 AquaLab 13. Further Reading Enigl, D.C. and K.M. Sorrels. (1997). Water Activity and Self-Preserving Formulas. In: Preservative-Free and Self- Preserving Cosmetics and Drugs: Principles and Practice. Kabara, J.J. and D.S. Orth (ed.) Marcel Dekker, pp. 45-73. Hageman, M.J. (1988). The role of moisture in protein sta- bility.

  • Page 93: Miscellaneous

    AquaLab 13. Further Reading Miscellaneous Bell, L.N. and T.P. Labuza. (1992). Compositional influ- ence on the pH of reduced-moisture solutions. Journal 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 reaction kinetics.
  • Page 94 AquaLab 13. Further Reading senschaft und-Technologie. 18:111-117. Lomauro, C.J., A.S. Bakshi, and T.P. Labuza. (1985). Eval- uation of food moisture sorption isotherm equations. Part II: Milk, coffee, tea, nuts, oilseeds, spices and starchy foods. Lebensmittel-Wissenschaft und-Technologie. 18:118-124. Yasuda, H., H.G. Olf, B. Crist, C.E. Lamaze, and A. Peter- lin.

  • Page 95: Preparing Salt Solution

    AquaLab Appendix A Appendix A Preparing Salt Solution If you choose to mix a saturated salt solution for use as a calibration standard, we recommend that you use the approved AOAC method. This method is as follows: 1. Select a reagent-grade salt and place it in a test con- tainer to a depth of about 4cm for more soluble salts (lower water activity), to a depth of about 1.5 cm for less soluble salts (high water activity), and to an inter-...
  • Page 96 AquaLab Appendix A standard error for each salt solution, not the AquaLab’s accuracy in measuring the salt. AquaLab measures all samples with an accuracy of ±0.003a 4. Saturated salt solutions are very temperature-sensitive and their values are not as accurate as the calibration standards offered by Decagon.

  • Page 97: Appendix B

    AquaLab Appendix B Appendix B Table 2: Temperature Correction of Decagon’s Calibration Standards Temp. 0.5m 6.0m 8.57m 13.41m (°C) NaCl LiCl LiCl 15.0 1.000 0.984 0.761 0.492 0.238 20.0 1.000 0.984 0.760 0.496 0.245 25.0 1.000 0.984 0.760 0.500 0.250 30.0 1.000 0.984...

  • Page 98: Declaration Of Conformity

    All instruments are built at the factory at Decagon and pertinent testing documentation is freely available for verication. This certification applies to all AquaLab Series 3 models, including, but not limited to, the Series 3 and 3TE.

  • Page 99: Certificate Of Traceability

    AquaLab Certificate of Traceability Certificate of Traceability Decagon Devices, Inc. 2365 NE Hopkins Court Pullman WA 99163 tel: (509) 332-2756 fax: (509) 332-5158 support@decagon.com This is to certify that AquaLab water activity meters are manufactured utilizing temperature standards with calibra- tion traceable to the National Institute of Standards and Technology (NIST).
  • Page 100 AquaLab Index Index Accessories 17 Accuracy 4 AquaLab and chilled mirror dewpoint technique 5 and temperature 6 limitations of 8 theory 9 Beeper 25 changing Block failure 61 Buttons for linear offset settings 37 for menu selection 21 C for continuous mode 23 Calibration 35 Calibration standards 33 Cautions 49...
  • Page 101 AquaLab Index Continuous sampling mode 23 Customer service 1 Czech 21 Danish 21 Declaration of Conformity 93 Dehydrated samples 44 Dried samples 43 Dry samples 50, 58, 59 Error messages 54 "sample too dry" 58, 59 "sample too hot" 58 triangle on screen 60 Exit 26 inside sample chamber 6...
  • Page 102 AquaLab Index Italian 21 Languages changing 21 LED 25 Linear offset causes for 33 definition 33 how to adjust for 35 menu 26 when to verify for 35 Location for sampling 18 Low water activity 46, 50 Main menu 19, 21 Maintenance 27 Manual 1 Material Safety Data Sheet 34...
  • Page 103 AquaLab Index Peltier cooler 6 Portuguese 21 Preparing salt solutions 90 Propylene glycol 46, 56 cleaning out of chamber 46 Read time affected by sample temp. 46 long read time 6, 43, 56 Readings cautions 49 how AquaLab takes 48, 49 taking readings 48 References 67 Relative humidity 5, 11...
  • Page 104 AquaLab Index dehydrated 44 dried 43 low water activity 46 multi-component 41 needing special preparation 43 not at room temperature 46 slow water-emitting 44 surface area of 44 viscous 44 Sampling modes continuous 23 normal 21 Saturated salts 90 Seller’s liability 3 Spanish 21 Spilling the sample 49 Swedish 21...
  • Page 105 AquaLab Index Troubleshooting 54 Verification 35 Verification standards 33 aw readings too high/low for 57 compared to saturated salts 91 Volatiles 8, 46 Warm-up 20 Warranty 2 Water activity adjusting for offset 39 Aqualab and 4 calibration standards 34 definition 5, 9 displayed 19 effect on food 5, 9 low 50, 51...

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