Home

AquaLabCX-2v3 AquaLab CX

1. A qualab and 5 definition 5 low 28 water bath 29
2. CX 2T e The CX 2T should be hooked up to a running water bath for at least one half hour before the unit is turned on This allows the water bath to reach a desired and accurate tem perature e When using your CX 2T it is important that the temperature of the drawer and the temperature of the sample are the same The sample to be measured should sit in the tempera ture tray for at least 3 minutes before any measurements are taken e When running the CX 2T with a water bath the instru 31 AquaLab Temperature Control ment s case fan must always be turned off When the water bath is not employed the fan must remain on The switch controlling the case fan is located on the instru ment s back panel above the fan filter e Thecase fan keeps the block temperature constant when the water bath is not in use This helps to ensure accurate read ings When a water bath is employed the water maintains the block temperature If the case fan is on at this time it will cool the block to a temperature lower than the sample causing condensation within the block and faulty readings e As the temperature of the CX 2T increases water activity readings will decrease It is necessary to adjust for an offset when the instrument is run at different temperatures Instructions for this process are located in Chapter 7 of this manual Note Do not try to chill the CX 2T usinga water bath Dew will form throughout the sample chamber causing
3. T P Labuza 1985 Evaluation of food moisture sorption isotherm equations Part Fruit vegetable and meat products Lebensmittel Wissenschaft und Technologie 18 111 117 Lomauro CJ AS Bakshi and T P Labuza 1985 Evaluation of food moisture sorption isotherm equations Part Il Milk coffee tea nuts oilseeds spices and starchy foods Lebensmittel Wissenschaft und Technologie 18 118 124 Yasuda H H G Olf B Crist CE Lamaze and A Peterlin 1972 Movement of water in homogeneous water swollen polymers In Water Structure at the Water Polymer 70 AquaLab Further Reading Interface Jellinek H H G ed Plenum Press New York London 71 AquaLab Appendix A Appendix A Salt Solutions Preparing Salt Solution If you choose to mix a saturated salt solution for use as a verification 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 container to a depth of about 4cm for more soluble salts lower aw to a depth of about 15 cm for less soluble salts high aw and to an intermediate depth for intermediate salts 2 Add distilled water in increments of about 2mL stirring con stantly 3 Add water until the salt can absorb no more water as evi denced by the presence of free liquid Keep the amount of free liquid to the minimum needed to keep the solution satu rated with water If you intend
4. and at any voltage near 110 120 220 or 240 volts The voltage setting can easily be changed by rotating a tab inside the power module The power module is located in the lower right corner of the instrument s back panel AquaLab CX2 serial number B96 1082 Docsgon Devices Inc WARNING 3 DANGER OF ELECTRIC SHOCK EL LD TE 270 CEs DISCONNECT AC POWER a z BEFORE REMOVING COVER apan ON REAR C SERIAL vO power module e Unplug AquaLab s power cord before checking or changing the voltage 10 AquaLab Getting Started e Slide the plastic cover to the left to expose the fuse chamber e Remove the fuse by pulling out the fuse pull lever located under the fuse to the right fuse LINE FREQUENCY ASE ONLYWITH 250V FUBE AE AAOME J 1OOVIT IS VII 20VI220VI239VI220 voltage board fuse pull lever When the fuse has been removed the voltage board a small light colored board located in the bottom of the fuse chamber will be visible The current voltage setting is displayed in the back left hand corner If this voltage matches the voltage of the power source to be used replace the fuse and continue setting up AquaLab If the two do not match the voltage tab needs to be changed to match the correct line voltage To change the voltage e Remove the tab by inserting a small screwdriver or awl into the hole at the center bottom of the power module chamber e Slide the tool under the tab and hook it into
5. are influenced by potentials that affect the binding of water These include matric potentials chemical bonding energies osmotic potentials gravitational potentials and pressure potentials Matric chemical bonding and osmotic potentials are very important in their relation to water activity in foods By altering any of these potentials the a of a sample may also be altered Matric potential refers to the sample s structure and its ability to hold water within that structure through capillary and surface tensions Chemical bonding energy refers to the energy of chemical water bonds within a sample Osmotic potential refers to not only the potential energies exerted on water across semi permeable membranes but also to the energy a microorganism might exert on a sample in order to take on water If the water within a sample is tightly bound a microorganism will find it hard to survive If you would like more information about water activity in foods please contact Decagon We have a collection of papers written about water activity in a variety of applications We can send you a copy of the articles or you may find what you need in the reference section of this manual 39 AquaLab Cleaning and Maintenance 10 Cleaning and Maintenance The accuracy of your AquaLab is vitally dependent on keeping your instrument clean Because of this we include a prepared cleaning kit with each AquaLab to ensure that you have the rig
6. different methods Journal of Food Science 41910 917 Prior BA 1979 Measurement of water activity in foods A review Journal of Food Protection 42 8 668 674 Reid DS 1976 Water activity concepts in intermediate moisture foods In Intermediate Moisture Foods Davies R GG Birch and KJ Parker ed Applied Science Publishers London pp 54 65 Richard J and T P Labuza 1990 Rapid determination of the water activity of some reference solutions culture media and cheese using a new dew point apparatus Sciences des Aliments 10 57 64 Roa V and MS Tapia de Daza 1991 Evaluation of water activity measurements with a dew point electronic humidity meter Lebensmittel Wissenschaft und Technologie 24 3 208 213 Roos K D 1975 Estimation of water activity in intermediate moisture foods Food Technology 29 26 30 Scott V N and DT Bernard 1983 Influence of temperature on the measurement of water activity of food and salt systems Journal of Food Science 48 552 554 Snavely MJ J C Price and H W Jun 1990 A comparison of three equilibrium relative humidity measuring devices Drug Development and Industrial Pharmacy 16 8 1399 1400 Stamp JA S Linscott C Lomauro and T P Labuza 1984 Measurement of water activity of salt solutions and foods by several electronic methods as compared to 57 AquaLab Further Reading direct vapor pressure measurement Journal of Food Scienc
7. kind of fuse or you will risk damage to your instrument as well as void your warranty 4 Replace the fuse holder and push it into the fuse well until the release tab snaps in place 5 Re connect the power cord and turn your instrument on If the fuse blows again a failed component may be causing the problem Contact Decagon to make arrangements for repairs PROBLEM The instrument s display doesn t go to zeroes a short while after turning it on SOLUTION e Some of the AquaLab s components may be damaged The garbage that shows on the display when AquaLab is first turned on should disappear after about thirty seconds If it doesn t some of the internal components may be damaged and you may have to return your AquaLab for repair See Chapter 11 for repair instructions 52 AquaLab Troubleshooting PROBLEM Readings are slow or inconsistent SOLUTION The sample chamber may be dirty Refer to Chapter 10 of the manual for directions on cleaning the sample chamber Some foods absorb or desorb moisture so slowly that mea surements take longer than usual and nothing can be done to speed up the process Refer to Chapter 5 for further expla nation Your sample may contain propylene glycol This com pound is known to cause unstable readings because it con denses on the surface of the chilled mirror and alters readings Please refer to the propylene glycol section in Chapter 5 for hints on redu
8. manual How it works AquaLab uses the chilled mirror dew point technique to measure the a of a sample This technique is a primary measurement method of relative humidity When a sample is measured with AquaLab a stainless steel mirror within the chamber is repeatedly cooled and heated As it does so dew is continually forming and evaporating The instrument s fan circulates air in the sensing chamber which speeds up the equilibration process Each time dew forms on the mirror AquaLab measures the temperature and calculates a of the sample Each a value is saved and compared to previous values as it makes new AquaLab A bout A quaLab readings When the a values of any two readings are less than 001 apart the instrument has reached equilibrium and the measurement process stops AquaLab then signals you by beeping The final water activity and temperature of the sample is then displayed With AquaLab temperature control is unnecessary for most applications The change in a due to temperature change for most materials is less than 002 per degree Celsius Therefore model CX 2 is ideal for the measurement of samples at room temperature However samples that are not at room temperature during the read cycle will equilibrate to the temperature of AquaLab This variable temperature will cause longer reading times since a complete and accurate reading will not be made until the sample and the instrument are within 2 degre
9. sample equilibration by restarting the read cycle while keeping the chamber sealed Dehydrated Samples Some extremely dry samples such as dehydrated foods because of their moisture sorption characteristics also have increased reading times AquaLab may require up to ten minutes to reach an accurate measurement of a Nothing can be done to decrease the reading times of some dehydrated samples Propylene Glycol AquaLab will give accurate readings on most alcohols However samples with high levels of propylene glycol require special sampling procedures to get accurate readings If your sample contains propylene glycol in levels of less than 10 there will probably be no effect on the accuracy of consecutive a readings Samples that contain propylene glycol in concentrations higher than 10 will not damage the instrument but a values for consecutive samples will not be accurate unless certain precautions are taken Propylene glycol condenses on the mirror during the reading process but it never evaporates from the mirror as water does As a result the very first reading will be somewhat accurate but subsequent readings will not be accurate unless you clear the condensed propylene glycol out of the chamber after each reading This is 24 AquaLab Sample Preparation done by running a sample consisting of activated charcoal after each propylene glycol bearing sample Another option is to clean the chamber as described in
10. sample material left on the cup rim will be transferred to the block preventing this seal and contami nating future samples 5 If the same sample will be read at some other time put the sample cup s disposable lid on the cup to restrict water transfer To seal the cap place tape completely around the cup lid junction It is necessary to seal the cup if it will be a long time before the measurement is made Materials Needing Special Preparation AquaLab reads most materials in less than five minutes depending on which mode you are operating in Some samples however may require longer reading times due to the nature of the material you are sampling These materials need additional preparation to ensure quick accurate readings To find out whether special sample preparation is necessary take a reading and see how long it takes to find the water activity If it takes 22 AquaLab Sample Preparation longer than six minutes remove the sample and take a reading of a verification standard This will ensure that the sample itself is causing the long read time and that there is not a problem with your instrument If the verification standard also takes longer than six minutes to sample refer to Chapter 12 of this manual for more information Coated and Dried Samples Samples that have coatings such as sugar or fat often require longer reading times This is because it takes longer for the samples to equilibrate If this is
11. the hole in the center front of the tab You may need to hold the fuse pull 11 AquaLab Getting Started lever as you slide the tab gently out The tab allows you to select between four voltage settings 100 120 220 and 240 If your power source does not exactly match one of these set tings choose the closest setting e Align the tab by rotating it until the number corresponding to the voltage you want is right side up and facing you Slide the tab back into position The correct voltage should now be displayed in the back left hand corner e Carefully replace the fuse and slide the plastic cover over the fuse chamber Preparing AquaLab for Operation After finding a good location to do your sampling and checking the voltage plug the power cord to the back of the unit Before turning it on pull open the sample drawer turn the knob to the OPEN LOAD position An empty disposable sample cup is usually placed upside down in the drawer to protect it during shipment Remove this sample cup and turn the instrument on The ON OFF switch is located on the lower left corner of the AquaLab s front panel When you turn it on all the segments on the LCD will appear like 8 s across the screen Within 30 seconds the display should show all zeroes ARS OPEN LOAI POWER E In order to provide the most accurate readings AquaLab should 12 AquaLab Getting Started ideally be allowed a wa
12. which is the ratio of water vapor pressure above any sample to the water vapor pressure of pure water at the same temperature Samples with no free water will have an a of 0 000 while a sample such as pure water will have an a of 1000 There are two basic types of water analysis The first is a quantitative or volumetric analysis to determine the water content of a sample Typically the sample is first weighed then oven dried and reweighed to measure its total water content But merely knowing the water content of a sample does not give an indication of the physical properties of that water The question is not how much water is in a sample but how much of that water is available to be used by microorganisms or other destructive agents The second type of water analysis the measurement of water activity answers this question Water activity is an energy measurement which defines the amount of unbound water in a sample Because microorganisms require water for survival too 38 AquaLab Theory W ater Activity in Foods much free water in a sample can serve as a medium for microbial reproduction travel and contamination If water within a sample is held with enough force microorganisms will not be able to exert the energy required to obtain water necessary for their subsistence Because of this a is commonly used in the evaluation of quality and safety of foods drugs and cosmetics Energy measurements
13. 343 G mez R Fernandez Salguero J MA Carmona and D Sanchez 1993 Water activity in foods with intermediate moisture levels Bakery and confectionery products 67 AquaLab Further Reading Miscellany Alimentaria 30 55 57 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 CG Biliaderis and W Bushuk 1992 Effect of added pentosans on some properties of wheat bread Food Chemistry 43 251 257 Ramanathan S and S Cenkowski 1995 Sorption isotherms of flour and flow behaviour of dough as influenced by flour compaction Canadian Agricultural Engineering 37 19 124 Roessler P F and M C Ballenger 1996 Contamination of an unpreserved semisoft baked cookie with a xerophilic Aspergillus species Journal of Food Protection 59 1055 1060 Seiler DAL 1979 The mould free shelf life of bakery products FMBRA Bulletin April 2 71 74 Sumner S S JA Albrecht and D L Peters 1993 Occurrence of enterotoxigenic strains of Staphylococcus aureus and enterotoxin production in bakery products Journal of Food Protection 56 722 724 Tesch R M D Normand and M Peleg 1996 Comparison of the acoustic and mechanical signatures of two cellular crunchy cereal foods at various water activity levels Journal of the Science of Food and Agriculture 70 347 354 Weegels PL JA Ver
14. 51 F fan blade 41 43 fan filter 32 fax number 2 features 8 L linear offset 55 Causes for 14 definition 14 how to adjust for 18 18 20 when to verify for 18 loaners 50 location 9 low water activity 25 28 M maintenance 40 manual 1 microbial growth related to water activity 38 O offset 32 O rings 44 45 P pharmaceuticals 69 powdery samples 28 preparing salt solutions 72 propylene glycol 6 24 53 R read time 6 long read time 6 22 53 readings cautions 27 how Aqualab takes 26 27 taking readings 26 references 56 baked goods and cereals 67 beverages Soups sauces preserves 68 dairy products 65 food quality and safety 59 meat and seafood 63 microbiology 60 pharmaceuticals 69 water activity theory 56 relative humidity 38 repair costs 49 repair instructions 48 S salt solutions uncertainty using saturated solutions 15 salt standards See verification standards Sample cup 45 Sample cups filling level 22 sealing 22 sample draw er 44 sample preparation 21 sample temperature and CX2 T 31 saturated salts 72 seller s liability 3 Shipping 48 T technical assistance 55 technical support 1 telephone number 1 temperature hot samples 27 of instrument 27 samples not at room temp 25 temperature control 6 29 theory water activity 56 troubleshooting 51 V verification standards 14 equations 16 table of values 17 voltage settings 12 W warm up 13 warranty 3 water activity
15. 7 46 Wijtzes T PJ Mcclure MH Zwietering and TA Roberts 1993 Modelling bacterial growth of Listeria monocytogenes as a function of water activity pH and temperature International Journal of Food Microbiology 18 139 149 Zw ietering MH T Wijtzes J C De Wit and RK VanT 1992 A decision support system for prediction of the microbial spoilage in foods Journal of Food Protection 55 973 979 W ater Activity in Foods Meat and Seafood Chen N and LA Shelef 1992 Relationship between water activity salts of lactic acid and growth of Listeria monocytogenes in a meat model system Journal of Food Protection 55574 578 Clavero MRS and LR 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 Environmental Microbiology 62 2735 2740 Duffy LL P B Vanderlinde and F H Grau 1994 Growth of 63 AquaLab Further Reading Listeria monocytogenes on vacuum packed cooked meats Effects of pH a w nitrite and ascorbate International Journal of Food Microbiology 23 377 390 Fernandez Salguero J R G mez and MA Carmona 1994 Water activity of Spanish intermediate moisture meat products Meat Science 38 341 346 G mez R and Fernandez Salguero J 1993 Note Water activity of Spanish intermediate moisture fish products Revista Espanola De Ciencia Y Tecn
16. 80 Comparative study of three methods of determining water activity in intermediate moisture foods Lebensmittel Wissenschaft und Technologie 13 169 173 Chirife J G Favetto C Ferro Fontan and S Resnik 1983 The water activity of standard saturated salt solutions in the range of intermediate moisture foods Lebensmittel Wissenschaft und Technologie 16 36 38 Duckworth R 1975 Water Relations of Foods Academic Press New York Gomez Diaz R 1992 Water activity in foods Determination methods Alimentaria 29 77 82 G mez R and Fernandez Salguero J 1992 Water activity and chemical composition of some food emulsions Food Chemistry 45 91 93 Greenspan L 1977 Humidity fixed points of binary saturated aqueous solutions Journal of Research of the National Bureau of Standards A Physics and Chemistry 81A 89 96 Karmas E 1981 Measurement of moisture content Cereal Foods World 26 7 332 334 Kitic D D C Pereira Jardim G Favetto SL Resnik and J Chirife 1986 Theoretical prediction of the water activity of standard saturated salt solutions at various temperatures 56 AquaLab Further Reading Journal of Food Science 511037 1042 Labuza T P and R Contreras Medellin 1981 Prediction of moisture protection requirements for foods Cereal Foods World 26 7 335 343 Labuza TP K Acott SR Tatini and RY Lee 1976 Water activity determination A collaborative study of
17. AQUA Water Activity Meter Operators Manual Version 3 0 Decagon Devices Inc AquaLab Table of Contents Table of Contents es 1 Introduction 1 A bout this M anual 1 Customer Service 1 Phone 1 Fax 2 E mail 2 W arranty 3 Note to our AquaLab Users 3 Seller s Liability 3 2 About AquaLab 5 How it works 5 Features 8 3 Getting Started 9 Components of your AquaLab 9 Choosing a Location 9 Checking and Changing Voltage Settings 10 Preparing AquaLab for O peration 2 4 Linear Offset and Verification Standards 14 W hat is Linear Offset 14 Verification Standards 14 Saturated Salt Solutions 5 A qualab s Verification Standards 16 W hen to Verify for Linear O ffset 18 How to Verify and Adjust for Linear O ffset 18 5 Sample Preparation 21 AquaLab Table of Contents 9 Preparing the Sample 21 M aterials Needing Special Preparation 22 Coated and Dried Samples 23 Speeding up Read time 23 Dehydrated Samples 24 Propylene Glycol 24 Low W ater Activity 25 Samples not at Room Temperature 25 Taking a Reading 26 How AquaLab takes Readings 27 Cautions 27 Temperature Control 29 Important Hints Concerning the CX 2T 31 Computer Interface 33 O utput Format 33 Using Hyperterminal in W indows 95 and W indowsNT 34 Using Terminal for W indows 3 0 and 3 1135 Using A quaLink 35 Theory Water Activity in Foods 38 10 Cleaning and Maintenance 40 Tools N
18. C 1995 Seafood microorganisms and seafood safety Journal of Food and Drug Analysis 333 144 Farber J M F Coates and E Daley 1992 Minimum water activity requirements for the growth of Listeria 60 AquaLab Further Reading monocytogenes Letters In Applied Microbiology 15 103 105 Garcia de Fernando G D O Diaz M Fernandez and J A Ordonez 1992 Changes in water activity of selected solid culture media throughout incubation Food Microbiology 9 77 82 Gibson AM J Baranyi J Pitt MJ Eyles and T A Roberts 1994 Predicting fungal growth The effect of water activity on Aspergillus flavus and related species International Journal of Food Microbiology 23 419 431 Goaleni N JE Smith J Lacey and G Gettinby 1997 Effects of temperature water activity and incubation time on production of aflatoxins and cyclopiazonic acid by an isolate of Aspergillus flavus in surface agar culture Applied and Environmental Microbiology 63 1048 1053 Hocking A D and B F Miscamble 1995 Water relations of some Zygomycetes isolated from food Mycological Research 99 113 1118 Hocking AD BF Miscamble and J I Pitt 1994 Water relations of Alternaria alternata Cladosporium cladosporioides Cladosporium sphaerospermum Curvularia lunata and Curvularia pallescens Mycological Research 98 91 94 Houtsma PC A Heuvelink J Dufrenne and S Notermans 1994 Effect of sodium lactate on toxin pro
19. Chapter 10 Low Water Activity Samples that have an a of less than 03 cannot be accurately measured However samples with such low a values are rare When a sample s a value is less than 03 AquaLab will display an error message informing you that your sample is too dry to be read If your sample is not extremely dry but is still getting the error message refer to the troubleshooting section of this manual for other possible explanations Samples not at Room Temperature Samples that are 4 degrees colder or warmer than the instrument chamber temperature will need to equilibrate to ambient temperature before a fast accurate reading can be made Rapid changes in temperature over short periods of time will cause the a readings to rise or fall until the temperature stabilizes Because the AquaLab is always comparing its previous and current results it will not terminate the read cycle until its compared readings are less than 001 apart Initial readings on colder or warmer samples should not be averaged Such measurements will not be accurate When the temperature stabilizes within one or two degrees of the chamber temperature you can proceed with normal measurements 25 AquaLab Taking a Reading 6 Taking a Reading 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 Place your pre
20. RTE BEFORE REMOVING COVER power cord plug fuse well linm ota adusimert de pin power switch sampio Gwar AquaLab Getting Started 3 Getting Started SS ee Components of your AquaLab Your AquaLab should have been shipped with the following items e AquaLab main unit e Power cord e 100 disposable sample cups e Operator s Manual e 3vials each of the following verification solutions 760 a NaCl 500 a LiCl 250 a LiCl Choosing a Location To ensure that your AquaLab operates correctly and consistently place it on a level surface This reduces the chance that sample material will spill and contaminate the inside of the instrument To protect the internal electrical components and to avoid inaccurate readings place your AquaLab in a location where the temperature remains fairly stable This location should be well AquaLab Linear O ffset and Verification Standards away from air conditioners heaters open windows outside doors refrigerator exhausts or other items that may cause rapid temperature fluctuation Checking and Changing Voltage Settings Users in the United States and Canada will not have to change AquaLab s voltage setting Users in other countries particularly those which supply power at 220V or 240V should check the voltage setting before using the instrument Your AquaLab may sustain damage if the voltage is incorrectly set AquaLab will operate at both 50 and 60Hz
21. ab s fan filter is designed to limit the intake of debris from the environment The accuracy of the instrument is dependent on a clean chamber Therefore the fan filter should be routinely checked and cleaned You may observe that your sample temperatures rise faster than usual when your fan filter becomes increasingly clogged with dust A clogged filter will reduce airflow inside your instrument making it more difficult to maintain the correct temperature balance between the block and the sample To clean the fan filter do the following 45 AquaLab Cleaning and Maintenance 1 2 4 5 Unplug your instrument Locate the fan guard filter at the back of the case Pry off the top plate of the fan guard to expose the foam rubber fil ter AquaLab CX2 serial number WARNING te DANGER OF ELECTRIC SHOCK s DISCONNECT AC POWER BEFORE REMOVING COVER location of the fan filter Remove the filter and rinse it under running water with the dusty side down to avoid forcing dust back into the filter Pat the filter dry with paper towels Replace the filter and snap the filter plate back in place Verifying Operation 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 cleaning procedures 46 AquaLab Cleaning and Maintenance Check the response of you
22. accuracy errors To read chilled products the entire instrument must be chilled For more detailed information regarding the operation of the CX 2T please refer to Appendix A 32 AquaLab Computer Interface 8 Computer Interface Your AquaLab has the capability to send water activity data to your computer for further analysis and storage To do this you can purchase an AquaLab RS 232 interface cable and a terminal program called AquaLink or you can use the RS 232 cable with your computer s own terminal program The RS 232 cable is specially designed for use with the CX 2 so other types will not work Output Format AquaLab data is output in comma delimited ASCII format Each time the AquaLab makes a measurement one line of information will be sent to the computer Here is an example illustrating the format in which it appears on screen 187 405 20 77 6 The first number that appears is from the datalogger and is not relevant to your measurments The second is the water activity value The third is the temperature in degrees Celsius at the timeof measurement and the fourth is the time in hours and minutes since AquaLab was turned on If AquaLab is left on for more than 24 hours the clock will reset to zero 33 AquaLab Computer Interface Using Hyperterminal in Windows 95 and Windows NT To use Hyperterminal with your AquaLab follow these steps 1 Press the Start button and select Programs gt Acce
23. afety and quality Trends in Food Science and Technology March 68 72 Hardman T M 1988 Water and Food Quality Elseiver Press 59 AquaLab Further Reading London Kress Rogers E 1993 Food quality measurement Food Industry News September 23 26 Levine H and L Slade 1991 Water Relationships in Foods Plenum Press New York Mannheim CH J X Liu and SG Gilbert 1994 Control of water in foods during storage Journal of Food Engineering 22 509 532 McMeekin T A and T Ross 1996 Shelf life prediction Status and future possibilities International Journal of Food Microbiology 33 65 83 Nelson KA and T P Labuza 1994 Water activity and food polymer science Implications of state on arrhenius and WLF models in predicting shelf life Journal of Food Engineering 22 271 289 Rockland LB and GF Stewart 1981 Water Activity Influences on Food Quality Academic Press New York Rockland L B and SK Nishi 1980 Influence of water activity on food product quality and stability Food Technology 34 42 59 Seow C C T T Teng and CH Quah 1988 Food Preservation by Moisture Control Elsevier New York Taoukis P W Breene and TP Labuza 1988 Intermediate moisture foods Advances in Cereal Science and Technology 9 914 28 Water Activity and Microbiology Beuchat L R 1981 Microbial stability as affected by water activity Cereal Foods World 26 7 345 349 Chen H
24. al Select Communications from the Settings menu Set the baud rate to 300 and make sure the other settings are as fol lows 8 data bits 1 stop bit no parity Select the COM port that you will be using Click OK Select Receive text file from the Transfers menu A pop up window will appear Type in a name for this terminal ses sion and click OK Begin sampling with your AquaLab The data will be dis played on screen as you sample When you are finished click on the Stop button on the bot tom left corner of the screen Terminal will save your data to the filename you indicated earlier If you wish you can open this file in a spreadsheet program and analyze the data further Using AquaLink AquaLink is a program that can only be used in DOS Therefore 35 AquaLab Computer Interface if your computer uses Windows 95 or higher you may not be able to use AquaLink If this is the case refer to the directions above for using HyperTerminal 1 Install AquaLink to your hard drive or run it from the floppy disk 2 Type AquaLink in the AquaLink directory to execute the program 3 Press return and begin taking readings with AquaLab The readings will be displayed on screen under three headings time a and temperature The time readings are real clock time according to your computer If your computer s clock is set to the correct time the time readings will be accurate 4 Save listed
25. al water bath Temperature control can be purchased as a feature on the AquaLab model CX 2T instrument or retrofit in an existing AquaLab model CX 2 Water is circulated from a user provided water bath through the sample drawer base and a temperature tray The temperature tray holds two samples and equilibrates them to the temperature of the drawer This speeds the reading 29 AquaLab Temperature Control process However the water bath should only be used for higher than ambient samples The temperature of the whole instrument needs to be altered when reading samples colder than AquaLab The coldest ambient temperature of AquaLab and the cold samples should not be below 5 C If you have purchased AquaLab with the temperature control feature you should have received e AquaLab fit with water ports and internal circulating base e Temperature Tray e Tygon tubing for connections 4 Elbows 2 with valves for the rear of AquaLab e 2without valves for the sample tray The drawer should be placed in the feed loop from the water bath and the temperature tray should be placed in the return path This keeps sample temperatures below the block temperature to ensure that unwanted condensation does not occur 30 AquaLab Temperature Control Water Flows Diagram of CX2T setup Note Water temperature settings and water circulation are controlled by the user provided water bath Important Hints Concerning the
26. ar offset prepare a sample cup half full of distilled water and make two readings The a read ing for the distilled water should be 1000 003 If it is not within this range clean the sensor chamber see Chapter 10 and repeat these instructions If it is reading within this 19 AquaLab Linear O ffset and Verification Standards range you can now measure samples accurately 8 If after adjusting for linear offset and cleaning the chamber you still are getting incorrect readings when reading verifi cation standards contact Decagon at 509 332 2756 1 800 755 2751in US and Canada for further instructions M easure Verification Standard Correct Not Correct M easure dH 50 A djust for O ffset Correct Not Correct OK to Sample Clean This flowchart is a graphical representation of the directions given above for checking for linear offset 20 AquaLab Sample Preparation 5 Sample Preparation Your AquaLab will continually provide accurate water activity measurements as long as its internal sensors are not contaminated by improperly prepared samples Careful preparation and loading of samples will lengthen time between necessary cleanings and will help you avoid costly repairs and down time Preparing the Sample To prepare a sample follow these steps 1 Make sure the material to be sampled is homogeneous Samples that combine wet an
27. b to ensure that the instrument performs to its full potential Customer Service If you ever need assistance with your AquaLab or if you just have questions there are several ways to contact us Phone Our toll free customer service number is available to our customers in the US and Canada Monday through Friday between 8 a m and 5 p m PST at 1800 755 2751L AquaLab Introduction For our customers outside of the US and Canada our regular telephone number is 509 332 2756 Fax Our fax number is 509 332 5158 When you fax us please include your AquaLab s serial number your name address phone and fax number along with a description of your problem so we can help you with your problem and then get back to you as soon as possible E mail If you need technical support you can send us messages via e mail at support decagon com Again please include as part of your message your AquaLab s serial number your name address phone fax number and return e mail address If you have a question about your application with AquaLab please send your message with the above information to aqualab decagon com AquaLab Introduction Warranty AquaLab has a 30 day satisfaction guarantee and a one year warranty on parts and labor To validate your warranty please complete and return the warranty card included with this manual You can return your warranty information by fax e mail phone or simply b
28. cing difficulties with measuring samples with propylene glycol If you have further questions regarding the measurement of propylene glycol contact Decagon Note As yet propylene glycol is the only volatile know to act unpredictably Glycerol and other alcohols used to flavor foods can usually be measured without problems however some aromatics may also caused unstable readings If this seems to be a problem for you contact Decagon A fan blade may be broken inside the block If even salt standards take a long time to read and the sample chamber is clean you may havea broken fan blade This is especially 53 AquaLab Troubleshooting likely if you have just cleaned the chamber If you suspect this may have happened contact Decagon for details on replacement The mirror or cooler may have become detached from the sample block Contact Decagon before sending it in for repair PROBLEM Water activity readings on verification standards are too high and a linear offset adjustment cannot be made any higher lower SOLUTION The thermopile in your chamber which measures sample temperature may have become contaminated Refer to Chapter 10 for directions on cleaning If you weren t using Decagon s performance verification standards high readings may indicate that the salt solution you are using is not in equilibrium PROBLEM When measuring samples AquaLab displays a LO message SOLUTION The sample
29. conditions Journal of Food Science 60 636 639 Dairy Products Fresno J M ME Tornadijo Carballo PJ Gonzalez and A Bernardo 1996 Characterization and biochemical 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 Korean Journal of Animal Science 33 387 391 Kombila ME and C Lacroix 1991 The effect of combinations of salt lactose and glycerol on the water activity Ay of cheese spreads Canadian Institute of Food Science and Technology Journal 24 233 238 Pisecky J 1992 Water activity of milk powders Milchwissenschaft 47 3 7 Tornadijo E J M Fresno J Carballo and SR Martin 1993 Study of Enterobacteriaceae throughout the manufacturing and ripening of hard goats cheese Journal of Applied Bacteriology 75 240 246 Valik L and F Gorner 1995 Effect of water activity adjusted with different solutes on growth and Lactic acid production by Lactobacillus helveticus Folia Microbiologica 40 472 474 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 65 AquaLab Further Reading Vivier D R Ratomahenina and P Galzy 1994 Characteristics of micrococci from the surface of Roquefort chees
30. d dry ingredients i e muffins with raisins or samples that have outside coatings like deep fried breaded foods can be measured but will take longer to equilibrate For samples like these AquaLab may take more than five minutes to give an accurate reading or it may require multiple readings of the same sample Measur ing the a of these types of foods is discussed more in depth later in this chapter see Materials Needing Special Prepara tion 2 Place the sample in a disposable sample cup completely covering the bottom of the cup if possible AquaLab is able to accurately measure a sample that does not or can not cover the bottom of the cup but a larger sample surface 21 AquaLab Sample Preparation area increases instrument efficiency by providing more sta ble infrared sample temperatures It also speeds up the read ing by shortening the time needed to reach vapor equilibrium 3 Do not fill the sample cup more than half full Overfilled cups will contaminate the sensors in the sensor chamber 4 Make sure that the rim and outside of the sample cup are clean Wipe any excess sample material from the rim of the cup with a clean tissue Material left on the rim or the out side of the cup will contaminate the sensor chamber and will be transferred to subsequent samples The rim of the cup is pushed up to form a vapor seal with the sensor block when the drawer knob is turned to the READ position Therefore any
31. duction spore germination and heat resistance of proteolytic Clostridium botulinum strains Journal of Food Protection 57 327 330 Kuntz LA 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 6 2 615 Marauska M A Vigants A Klincare D Upite E Kaminska and M Bekers 1996 Influence of water activity and 61 AquaLab Further Reading medium osmolality on the growth and acid production of Lactobacillus casei var alactosus Proceedings of the Latvian Academy of Sciences Section B Natural Exact and Applied Sciences 50 144 146 Miller AJ 1992 Combined water activity and solute effects on growth and survival of Listeria monocytogenes Scott A Journal of Food Protection 55414 418 Nakajo M and Y Moriyama 1993 Effect of pH and water activity on heat resistance of spores of Bacillus coagulans Journal of the Japanese Society for Food Science and Technology 40 268 271 Nolan DA D C Chamblin and J A Troller 1992 Minimal water activity levels for growth and survival of Listeria monocytogenes and Listeria innocua International Journal of Food Microbiology 16 323 335 Petersson S and J Schnuerer 1995 Biocontrol of mold growth in high moisture wheat stored under airtight conditions by Pichia anomala Pichia
32. e Journal of Applied Bacteriology 76 546 552 Fruits and Vegetables Ayub M R Khan S Wahab A Zeb and J Muhammad 1995 Effect of crystalline sweeteners on the water activity and shelf stability of osmotically dehydrated guava Sarhad Journal of Agriculture 11755 761 Beveridge T and SE Weintraub 1995 Effect of blanching pretreatment on color and texture of apple slices at various water activities Food Research International 28 83 86 Hubinger M F C Menegalli RJ Aguerre and C Suarez 1992 Water vapor adsorption isotherms of guava mango and pineapple Journal of Food Science 57 1405 1407 Jimenez M M Manez and E Hernandez 1996 Influence of water activity and temperature on the production of zearalenone in corn by three Fusarium species International Journal of Food Microbiology 29 417 421 Kiranoudis CT ZB Maroulis E Tsami and K D Marinos 1993 Equilibrium moisture content and heat of desorption of some vegetables Journal of Food Engineering 20 55 74 Makower B and GL Dehority 1943 Equilibrium moisture content of dehydrated vegetables Industrial and Engineering Chemistry 35 2 193 197 Maltini E D Torreggiani BR Brovetto and G Bertolo 1993 Functional properties of reduced moisture fruits as ingredients in food systems Food Research International 2643 419 Marin S V Sanchis and N Magan 1995 Water activity temperature and pH effects on growth of Fusariu
33. e 49 1139 1142 Stoloff L 1978 Calibration of water activity measuring instruments and devices Collaborative study Journal of Association of Official Analytical Chemists 611166 1178 Troller J A 1983 Methods to measure water activity Journal of Food Protection 46 129 134 Troller JA and J H B Christian 1978 Water Activity and Food Academic Press New York Troller J A and VAN Scott 1992 Measurement of water activity Aw and acidity In Compendium of Methods for the Microbiological Examination of Foods Vanderzant C and D F Splittstoesser ed American Public Health Association Washington D C pp 135 151 van den Berg C 1985 Water activity In Concentration and Drying of Foods MacCarthy D ed Elsevier London pp 11 35 van den Berg C 1991 Food water relations Progress and integration comments and thoughts In Water Relationships in Foods Levine H and L Slade ed Plenum Press New York van den Berg C and Bruin 1981 Water activity and its estimation in food systems Theoretical aspects In Water Activity Influences on Food Quality Rockland L B and GF Stewart ed Academic Press New York pp 161 Vega MH and G V Barbosa Canovas 1994 Prediction of water activity in food systems A review on theoretical models Revista Espanola De Ciencia Y Tecnologia De Alimentos 34 368 388 Vega MH B Romanach and GV Barbosa Canovas 1994 Prediction of water activ
34. eeded 40 Cleaning the Sensor Chamber Block 41 Cleaning the Fan Filter 45 Checking Calibration 46 11 Repair Instructions 48 Shipping Directions 48 Repair Costs 49 AquaLab Table of Contents Loaner Service 50 2 Troubleshooting 51 Problems and Solutions 51 B Further Reading 56 W ater Activity Theory and Measurement 56 Food Quality and Safety 59 W ater Activity and Microbiology 60 W ater Activity in Foods 63 M eat and Seafood 63 Dairy Products 65 Fruits and Vegetables 66 Baked Goods and Cereals 67 Beverages Soups Sauces Preserves 6 8 Pharmaceuticals 69 Miscellaneous 70 Appendix A Salt Solutions 72 Preparing Salt Solution 72 AquaLab Introduction 1 Introduction ES SS Welcome to Decagon s AquaLab model CX 2 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 researching or working on the production line AquaLab will suit your needs It is easy to use and provides accurate and timely results We hope you find this manual informative and helpful in understanding how to maximize the capabilities of your AquaLab About this Manual Included in this manual are instructions for setting up your AquaLab verifying the calibration of the instrument preparing samples and maintaining and caring for your instrument Please read these instructions before operating the AquaLa
35. es of each other For applications where temperature control is critical AquaLab can be operated in a controlled temperature chamber or room or you may purchase an AquaLab model CX 2T AquaLab is the fastest instrument for measuring water activity giving readings in five minutes or less Its readings are precise providing 0 003 accuracy The instrument is easy to clean and checking calibration is simple AquaLab has a few limitations however One of these is its ability to measure certain samples with high concentrations of propylene glycol which can condense on the surface of the chilled mirror Not all volatiles react this way glycerol for example has posed no problems and most other alcohols used to flavor foods are also measurable If your sample contains propylene glycol it is still possible to make accurate readings AquaLab A bout A quaLab Call Decagon for more details AquaLab may also have trouble measuring extremely dry substances with an a of less than 0 1 Some very dry or dehydrated foods absorb or desorb moisture in such a way that their readings may take longer than five minutes Black pepper for example causes faulty readings at first but after the initial gas has dissipated the sample can be read accurately AquaLab A bout A quaLab Features farvfan filter serial number label Aqualab CX2 serial number 898 1032 WARNING Decagon Device Inc main GLB sera AN A AC POWE PE
36. guilliermondii and Saccharomyces cerevisiae Applied and Environmental Microbiology 611027 1032 Pitt J 1 and BF Miscamble 1995 Water relations of Aspergillus flavus and closely related species Journal of Food Protection 58 86 90 Quintavalla S and G Parolari 1993 Effects of temperature aw and pH on the growth of Bacillus cells and spore A response surface methodology study International Journal of Food Microbiology 19 207 216 Saad R R 1992 Effect of water activity on growth and lipids of xerophilic fungi Aspergillus repens and Aspergillus amstelodami Zentralblatt Fuer Mikrobiologie 147 61 64 Santos J T M Lopez Diaz M L Garcia Lopez M C Garcia Fernandez and A Otero 1994 Minimum water activity for the growth of Aeromonas hydrophila as affected by 62 AquaLab Further Reading strain temperature and humectant Letters In Applied Microbiology 19 76 78 Tapia de Daza MS Y Villegas and A Martinez 1991 Minimal water activity for growth of Listeria monocytogenes as affected by solute and temperature International Journal of Food Microbiology 14 333 338 Tokuoka K and T Ishitani 1991 Minimum water activities for the growth of yeasts isolated from high sugar foods Journal of General and Applied Microbiology 37 111 119 Ucar F and Guneri 1996 The effect of water activity aw pH and temperature on the growth of osmophilic yeasts Turkish Journal of Biology 20 3
37. hoek A M G de Groot and RJ Hamer 1994 Effects of gluten of heating at different moisture contents Changes in functional properties Journal of Cereal Science 19 31 38 Beverages Soups Sauces Preserves Carson KJ J L Collins and MP Penfield 1994 Unrefined dried 68 AquaLab Further Reading apple pomace as a potential food ingredient Journal of Food Science 59 1213 T5 Durrani MJ R Khan M Saeed and A Khan 1992 Development of concentrated beverages from Anna apples with or without added preservatives by controlling activity of water for shelf stability Sarhad Journal of Agriculture 823 28 Ferragut V JA Salazar and A Chiralt 1993 Stability in the conservation of emulsified sauces low in oil content Alimentaria 30 67 69 Ibarz A J Pagan and R Miguelsanz 1992 Rheology of Clarified fruit juices Il Blackcurrant juices Journal of Food Engineering 15 63 74 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 International Journal of Food Science and Technology 28241248 Pharmaceuticals Cochet N and A L Demain 1996 Effect of water activity on production of beta lactam an
38. ht tools for effective cleaning Dust and sampling debris can contaminate the sampling chamber and must therefore be regularly cleaned out To clean your instrument carefully follow these instructions Tools Needed e Philips screwdriver e AquaLab Cleaning Kit If you have used up the components of your cleaning kit you may order another from Decagon or you can gather the following materials e lint free tissues like Kimwipe Note Do not use cotton swabs since they can leave an adhesive residue that can contaminate the mirror and block surfaces e Tweezers Distilled Water 40 AquaLab Cleaning and Maintenance e Isopropyl Alcohol Cleaning the Sensor Chamber Block 1 Unplug your AquaLab 2 Remove the eight screws that secure the cover located on each side of the AquaLab case Remove the cover Location of the case screws 3 Using a phillips screwdriver remove the four screws that secure the fan assembly to the block Location of the block screws 4 Carefully remove the fan assembly by lifting it straight up from the block There is a small fan on the under side of this lid The little blades break easily and AquaLab will not work properly when one breaks Treat this fan with care 41 AquaLab Cleaning and Maintenance 5 AquaLab s sensor mirror is located on top of the block between two round ports Take a blunt headed swab from your cleaning kit or a small piece of lint free tis
39. ile it is out of the block is of utmost importance Any broken fan blade must be replaced before it will be possible to get reliable a readings 6 Clean all surfaces of the block with the other swabs damp ened with water from the cleaning kit or a damp lint free tissue including the port holes on top 7 Lift up the sensor block and gently clean the thermopile it looks like an eye located on the bottom of the block Location of AquaLab s Thermopile 43 AquaLab Cleaning and Maintenance 8 Clean the lid of the chamber especially the small optical sensor found near the fan 9 Clean the sample drawer and its base Remove any debris from the inside of AquaLab Note When replacing the sample drawer be sureit is fit correctly into the base so that it will engage the switch on the bottom of the drawer Caution if the switch lever on the drawer gets behind the switch lever on the base it will break off the lever causing numerous problems 10 Recheck for debris then carefully insert the fan assembly into the block Align it so that the four screw holes match IL When replacing the sensor block make sure that the two alignment pins located on the lower section of the block are lined up with the holes on the drawer base You may have to gently force the pins into the holes in the base 2 Insert the four screws with the metal washers and O rings into the holes Turn them counter clockwise until a slight dro
40. ity in food systems A computer program for predicting water activity in multicomponent foods Revista Espanola De Ciencia Y Tecnologia De 58 AquaLab Further Reading Alimentos 34 427 440 Vos PT and T P Labuza 1974 Technique for measurements of water activity in the high ay range Journal of Agricultural and Food Chemistry 22 326 327 Voysey P 1993 An evaluation of the AquaLab CX 2 system for measuring water activity Digest Microbiology Section 124 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 September 41 48 Chirife J and B M Del Pilar 1994 Water activity glass transition and microbial stability in concentrated semimoist food systems Journal of Food Science 59 921 927 Chirife J and MP Buera 1995 A critical review of some non equilibrium situations and glass transitions on water activity values of foods in the microbiological growth range Journal of Food Engineering 25 531 552 Chirife J and MP Buera 1996 Water activity water glass dynamics and the control of microbiological growth 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 s
41. ke the following precautions to prevent contamination of the chamber When first loading the sample cover the case fan in the rear of the instrument with a piece of cardboard until the drawer is closed and locked this will prevent the fan which is always on from blowing your sample around inside of the instrument and chamber Once the sample drawer is pushed all the way in take the card away from the fan 28 AquaLab Temperature Control 7 Temperature Control eT Ee In the past water activity instruments have needed temperature control to make accurate sample readings AquaLab takes precision measurements of the air dew point temperature and the sample temperature then uses a microprocessor controlled algorithm to convert these temperatures and other critical information into a water activity reading AquaLab s water activity readings are therefore accurate without temperature control Users constructing and studying moisture sorption isotherms referencing a particular temperature or testing samples more than four degrees Celsius higher than the ambient temperature may want to have temperature control There are several options for controlling AquaLab s temperature One is to use an incubator or hot cold room set at the desired temperature This method is usually satisfactory for users with access to those facilities AquaLab is also available with a temperature control feature which allows it to be connected to an extern
42. lts Robinson and Stokes 1965 give activity coefficient for various salt solutions These can be used to compute the water potential or partial specific Gibbs free energy of the water in the solution using Y oycRT 1 where Y is the water potential is the number of active particles per molecule of solute i e 2 for NaCl yis the activity coefficient c is the concentration of the solute mol kg Ris the gas constant 8 314 J mol K and T is the Kelvin temperature Water potential is related to water activity by the equation YM a exp RT where My is the molecular weight of water 0 018 kg mol When equations land 2 are combined a simplified equation for 2 16 AquaLab Linear O ffset and Verification Standards water activity is obtained a exp oycM 3 For example equation 3 gives the ay in a 6M NaCl solution My 0 018 kg mol 2 and y 1271 from tables in Robinson and Stokes 1965 as a exp 2 x 1 271 x6 x 0 018 0 760 It is important to note that equation 3 has no explicit temperature dependence Available data on temperature dependence of y indicates that its variation is less than 2 over the range 0 to 50 C for NaCl Lang 1967 and KCI Campbell and Gardner 1971 and no other terms have any temperature dependence A further advantage of unsaturated salts is that there is no solid phase present to affect the water activity of the solution Salt in sa
43. m moniliforme and Fusarium proliferatum isolates from 66 AquaLab Further Reading maize Canadian Journal of Microbiology 411063 1070 Monsalve Gonzalez GV Barbosa Canovas and RP Cavalieri 1993 Mass transfer and textural changes during processing of apples by combined methods Journal of Food Science 58 1118 1124 Tapia de Daza MS CE Aguilar V Roa and RV Diaz de Tablante 1995 Combined stress effects on growth of Zy gosaccharomyces rouxii from an intermediate moisture papaya product Journal of Food Science 60 356 359 Zeb A R Khan A Khan M Saeed and SA Manan 1994 Influence of crystalline sucrose and chemical preservatives on the water activity and shelf stability of intermediate banana chips Sarhad Journal of Agriculture 10 72 726 Zhang X W X Liu DX Gu W Zhou RL Wang and P Liu 1996 Desorption isotherms of some vegetables Journal of the Science of Food and Agriculture 70 303 306 Baked Goods and Cereals Aramouni FM KK Kone J A Craig and D Y C Fung 1994 Growth of Clostridium sporogenes PA 3679 in home style canned quick breads Journal of Food Protection 57 882 886 Cahagnier B L Lesage and M D Richard 1993 Mould growth and conidiation in cereal grains as affected by water activity and temperature Letters In Applied Microbiology 177 B Clawson AR and AJ Taylor 1993 Chemical changes during cooking of wheat Food Chemistry 47337
44. mpling make sure that your standard is at ambient temperature before you load it into the sample drawer and that your AquaLab has warmed up long enough to make accurate readings 18 AquaLab Linear O ffset and Verification Standards Empty the whole vial of solution into a sample cup and place it in the AquaLab s sample drawer Carefully slide the drawer closed being especially careful so the solution won t splash or spill and contaminate the chamber Turn the drawer knob to the READ position to make an a reading Make two readings The a readings should be within 003 of the given value for your salt solution If your AquaLab is reading within 003 of the salt solution prepare a sample cup half full of distilled water and make two readings the first reading may be low The a reading should be 1000 003 If your salt reading is correct and your distilled water reading is not it is probably due to con tamination of the sensor chamber For cleaning instructions see Chapter 10 After cleaning repeat these instructions If you consistently get readings that are outside of the a of your salt solution by more than 003 a linear offset has probably occurred In this case adjust the reading on the AquaLab to the correct value This is done by twisting the potentiometer located on the left side of the screen with a small flat head screwdriver while the AquaLab is still beep ing After adjusting for line
45. ologia De Alimentos 33 651 656 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 Journal of Food Protection 59 1007 1010 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 Rocha Garza A E and J F Zayas 1996 Quality of broiled beef patties supplemented with wheat germ protein flour Journal of Food Science 61418 421 Shimasaki T K Miake Y Tsukamasa MA Sugiyama Y Minegishi and H Shinano 1994 Effect of Water Activity and Storage Temperature on the Quality and Microflora of Smoked Salmon Nippon Suisan Gakkaishi 60 569 576 Untermann F and C Muller 1992 Influence of ay value and storage temperature on the multiplication and enterotoxin formation of staphylococci in dry cured raw hams International Journal of Food Microbiology 16 109 64 AquaLab Further Reading 15 Williams SK GE Rodrick and R L West 1995 Sodium lactate affects shelf life and consumer acceptance of fresh Ictalurus nebulosus marmoratus fillets under simulated retail
46. on using this solution over a long term period make sure to seal the solution well to pre vent losses from evaporation Below is a table of saturated salt solutions and their respective water activities at differ 72 AquaLab Appendix A ent temperatures Please note that these values are Table t Water Activity Table for Selected Salt Solutions Saturated Salt Solution ay at20 C aw at25 C Lithium C hloride B 003 IB 003 M agnesium C hloride 331 002 328 002 Potassium C arbonate 432 003 432 004 M agnesium N itrate 544 002 529 002 Sodium Chloride 755 001 153 001 Potassium C hloride 851 003 843 003 Potassium Sulfate 976 005 973 005 Adapted from Greenspan 1977 Numbers rounded to nearest thousandth based on averaged published data Saturated salt solutions are temperature sensitive and their values are not as accurate as the verification standards offered by Decagon 73 Index En ees Symbols LO 43 A appendix 72 C case fan 32 cautions 27 checking calibration 46 chilled products 32 chilled mirror technique 5 cleaning 40 42 45 fan filter 45 sensor block 41 coated samples speeding read time for 23 components 9 cotton swabs 40 customer service 1 CX 2T 29 D dehydrated samples 24 dew point 29 downloading using Terminal for W indow s 35 dried samples speeding read time for 23 dry samples 7 E e mail address 2 error messages
47. ons including death or to property or things of whatsoever kind including but not without limitation loss of anticipated profits occasioned by or arising out of the installation operation use misuse nonuse repair or replacement of said material and equipment or out of the use of any method or process for which the same may be employed The use of this equipment constitutes Buyer s acceptance of the terms set forth in this warranty There are no understandings representations or warranties of any kind express implied statutory or otherwise including but without limitation the implied warranties of merchantability and fitness for a particular purpose not expressly set forth herein AquaLab A bout A quaLab 2 A bout A quaLab a ee a Water activity ay is the measurement used to determine how tightly water is structurally or chemically bound within a substance Not only is it a vapor pressure ratio but it can also be considered equal to the relative humidity of air in a sealed chamber that is equilibrated with a substance One of the most common uses for the AquaLab is to measure the a of food samples a influences color odor flavor texture and shelf life of a food product If a is not controlled the quality and safety of a product may suffer as a result For a more detailed description of water activity in food samples please refer to Chapter 9 titled Theory Water Activity in Foods of this
48. p in the screw height is felt or seen Turn the screws clockwise until they are secure All four screws should be tightened equally to form a seal between the fan and the block Note These screws may resist tightening If thereis any resistance do not force then Turn the screw counterclockwise until a little drop is fat and then turn it clockwise to tighten If these screws are forced it will cause stripping and they will not fully tighten Thisin turn will prevent the chamber from sealing as it should 44 AquaLab Cleaning and Maintenance 4 and any following readings will be inaccurate Adjust the screws so that there is pressure on the sample cup when the knob is turned This ensures that the chamber is sealed Test the tightness of the screws by placing an empty sample cup in the drawer and turning the knob to read If the knob is too easy to turn the screws need to be tightened Your instrument is equipped with O rings under the screws don t compress them The O rings help ensure proper sealing of the chamber during the read cycle without over tighten ing of the screws Replace AquaLab s outer case Make sure the holes in the case align with the holes in the main unit before inserting and tightening the screws Note The outer case should always be in place when mea suring a For ease of cleaning the cover screws could be left out or reduced to one or two Cleaning the Fan Filter Your AquaL
49. pared sample in the drawer Check the top lip of the cup to make sure it is free from sample residue remember an over filled sample cup may contaminate the chamber s sensors Carefully slide the drawer closed being especially careful if you havea liquid sample that may splash or spill and con taminate the chamber Turn the sample drawer knob to the READ position to seal the sample cup with the chamber This will start the read cycle In about 3 minutes the first a measurement will be displayed on the LCD Length of read times may vary depend ing on how dry your sample is Note Samples that have a large differencein a from previous samples may need extra time to reach equilibrium since some of the previous sample s atmosphere stays in the chamber after measurement 26 AquaLab Taking a Reading How AquaLab takes Readings AquaLab s reading cycle continues until two consecutive readings are within 0 001 of each other The instrument crosses the dew threshold numerous times to ensure the accuracy of readings When the instrument has finished its read cycle the aw is displayed accompanied by the beeper Cautions Never leave a sample in your AquaLab after a reading has been taken The sample may spill and contaminate the instrument s chamber if the instrument is accidentally moved or jolted e Do not overfill the sample dish e Never try to move your instrument after a sample has been loaded Movement ma
50. r instrument by measuring the water activity of both a verification standard and a distilled water sample If a linear offset has occurred refer to Chapter 4 for directions on how to correct for linear offset If after adjusting for linear offset your instrument is still not reading samples correctly contact Decagon for technical support 47 AquaLab Repair Instructions IL Repair Instructions eae ee eee If your AquaLab ever needs to be sent in for service or repair call Decagon at 509 332 2756 or 1 800 755 2751 US and Canada or fax us at 509 332 5158 We will ask you for your address phone number and serial number For non warranty repairs we will also ask for a purchase order number a repair budget and billing address Note If you purchased your AquaLab from one of our international distributors please contact them before contacting Decagon They may be able to provide you with local service and help you remedy the problem Shipping Directions When you ship your instrument back to us please include with it a document with the complete shipping address name and department of the person responsible for the instrument and most importantly a description of the problem This information will better help our technicians and our shipping department to expedite repair on your instrument and ship it back to you in good time Following are steps that will help in safely shipping your instrument back to u
51. readings to disk at any time by pressing the F1 key 5 When you select F1 the program will prompt you to enter a file name If you wish to save data to a different drive or directory than the one where AquaLink is stored specify that drive and directory with the file name All data will be saved to this file Note If you wish to use a spreadsheet to analyze your data you may want to use a particular extension For example comma delimited files must have the extension xls to be read by Microsoft Excel Check your spreadsheet user s manual for more information AquaLink can display up to 2000 readings before saving However we recommend saving more frequently to guard 36 AquaLab Computer Interface against data loss If you enter the same file name at the file name prompt AquaLink will append data to the existing file No data will be lost 6 To exit the program press F2 If some of the data has not been saved AquaLink will prompt Data not saved Are you sure you want to quit y n Make sure your data has been saved and then exit 37 AquaLab Theory W ater A ctivity in Foods 9 Theory Water Activity in Foods ae EC a Water Activity a is a measurement of water energy It indicates the amount of free water in a sample Free water refers to the water molecules in a sample that are not chemically or physically bound ay is equivalent to Equilibrium Relative Humidity ERH
52. rm up period of 15 minutes to an hour after turning it on This allows the air inside the AquaLab to equilibrate to the temperature of its surroundings It is also helpful to prepare a sample and take some readings during this equilibration period in order to warm up the sample chamber For instructions on how to prepare samples and take readings refer to Chapters 5 and 6 of this manual 13 AquaLab Linear O ffset and Verification Standards 4 Linear Offset and Verification Standards W hat is Linear Offset AquaLab uses the chilled mirror dew point technique for measur ing water activity Because this is a primary measurement meth od of relative humidity no calibration is necessary however it is important to check for linear offset periodically The components that the instrument uses to measure a are subject to changes that may affect AquaLab s performance These changes are usual ly the result of chamber contamination When this occurs it changes the accuracy of your readings This is what is called a linear offset Therefore frequent linear offset verification can assure you that your AquaLab is performing correctly Linear off set can be checked by using a salt solution and distilled water AquaLab should be checked for linear offset daily For high use or batch processing the instrument should be checked more often against a known standard of similar water activity Checking the water activity of a s
53. s 1 If possible ship your AquaLab back to us in its original card board box with foam inserts If this is not possible use a box 48 AquaLab Repair Instructions that has at least 4 inches of space between your instrument and each wall of the box 2 Put your instrument in a plastic bag to avoid disfiguring marks from the packaging 3 Don t ship your AquaLab to us with the power cord we have plenty here to use with your instrument 4 If you aren t using the foam inserts pack the box moder ately tight with packing material like styrofoam peanuts 5 Tape the box in both directions so it cannot be broken open in shipment 6 Include necessary paperwork so your repair can be pro cessed quickly This should include your name address serial number phone and fax numbers purchase order and a description of the problem Ship to Decagon Devices Inc ATTN Repair Department 950 NE Nelson Court Pullman WA 99163 Repair Costs Manufacturer s defects and instruments within the one year warranty will be repaired at no cost For non warranty repairs costs for parts labor and shipping will be billed to you We have a 50 minimum repair charge An extra fee will be charged for rush work Decagon will provide an estimated repair cost if 49 AquaLab Repair Instructions requested Loaner Service We have loaner instruments that can be provided while your instrument is being serviced There is ho
54. ssories gt Hyperterminal and click 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 In future downloads you will be able to click on this icon in have it already set up for you to download Click the OK but ton 3 A pop up menu labeled Connect To will appear Click on the scroll bar on the bottom of the screen labeled Connect Using and select the COM Port your RS 232 cable is con nected to 4 A pop up menu labeled COM Properties will appear show ing the port settings for the COM port you selected Make sure the settings are the following Baud rate 300 8 databits no parity 1stop bit and flow control set to hardware Click OK 5 Plug your RS 232 cable to the COM port you selected and connect it to your AquaLab Begin sampling AquaLab s data will be displayed on screen as it samples 6 When you are finished sampling you can print the data in the terminal session or save it 34 AquaLab Computer Interface Using Terminal for Windows 3 0 and 3 11 If you are operating under Windows 3 0 or 3 11 you can use the Terminal program to log your AquaLab s data as it reads Follow these instructions 1 Connect your RS 232 cable between the AquaLab and your computer Remember which COM port you are using Double click on the Accessories icon in Program Manager Open the icon labeled Termin
55. sue wrapped around the end of the tweezers and dip it into the distilled water so that it is wet but not soaked Gently wipe the mir ror Location of the sensor mirror Note If the mirror will not come clean using distilled water a small amount of 99 isopropyl or ethyl alcohol may be used followed by distilled water rinses Be careful if the swab is too wet with alcohol the seal around the mirror will be broken and require repair at Decagon Getting the mirror clean could be likened to getting laboratory glassware clean First use the necessary cleaners and then follow with several rinses After a thorough cleaning it is possible to check the effectiveness of the cleaning by running the instrument with the top off It is important when you do this that you unplug the fan motor Follow the wire from the motor on top of the 42 AquaLab Cleaning and Maintenance block lid to the small circuit board Disconnect this plug Turn the knob to read After about one minute the mirror will begin to fog Even fog formation over the entire mirror is an indication of a good cleaning Further cleaning of the mirror surface can be achieved by wiping the fog from the mirror as it forms with tissue as previously described Fogging will continue until the display reads LO or the knob is turned to open This procedure can be repeated as often as desired Taking care not to damage the fan blade by dropping it or running the fan wh
56. tandard solution and distilled water will alert you to the possibility of contamination of the unit or shifts in the linear offset from other causes Verification Standards Two choices Verification standards are specially prepared salt solutions that have a specific molality and water activity that is constant and accurately measurable There are two types of verification 14 AquaLab Linear O ffset and Verification Standards solutions saturated and non saturated The verification standards that were sent with your initial shipment are non saturated solutions and they are readily available from Decagon Devices These particular standards are accurate easy to use and are not temperature sensitive like saturated solutions can be Most importantly they greatly reduce preparation errors Because of these reasons we recommend using the standards provided by Decagon for the most accurate verification Decagon s Performance Verification Standards come in three water activity levels 0 760 0 500 and 0 250 a The standards are produced under a strict quality assurance regime The accuracy of the standards is verified by an independent third party and are shelf stable for one year Saturated Salt Solutions The water activity values listed in Appendix A for saturated salts were reprinted from Greenspan 1977 His method for determining water activity was to combine all of the available data from tests by other researchers The
57. the case for your samples don t worry that something is wrong with your instrument it simply means that your particular sample takes longer than most to exchange water with its outside environment Speeding up Read time To reduce the time needed to take an a reading for coated or dried samples one thing you can do is crush the sample before putting it in the sample cup Crushing increases the surface area of the sample thus decreasing reading times Keep in mind however that crushing some samples may alter their a readings For example a candy may havea soft chocolate center and a hard outer coating The a reading for the center and the outer coating are different so you need to evaluate which part of the sample you need to measure before crushing it When the candy is crushed the a will represent the average water activity of the entire sample whereas leaving the candy whole will give a reading for the coating which may act as a barrier to the center Another way to speed up readings for coated and dried samples 23 AquaLab Sample Preparation is to restart your AquaLab during its reading cycle To do this start the read cycle turn the sample drawer knob to the READ position and then wait 60 seconds Then turn the sample drawer knob from READ to the OPEN LOAD position then back to READ The instrument should beep again and the display should show zero for the a reading This action essentially speeds up
58. tibiotics by Streptomyces clavuligerus in submerged culture Journal of Applied Bacteriology 80 333 337 Costantino HR R Langer and A M Klibanov 1994 Solid phase aggregation of proteins under pharmaceutically relevant conditions Journal of Pharmaceutical Sciences 83 1662 1669 Heidemann D R and PJ Jarosz 1991 Performulation studies involving moisture uptake in solid dosage forms 69 AquaLab Further Reading Pharmaceutical Research 8 3 292 297 Miscellaneous Bell L N and T P Labuza 1992 Compositional influence on the pH of reduced moisture solutions Journal of Food Science 57 732 734 Bell L N and TP Labuza 1994 Influence of the low moisture state on pH and its implication for reaction kinetics Journal of Food Engineering 22 291 312 Bell L N 1995 Kinetics of non enzymatic browning in amorphous solid systems Distinguishing the effects of water activity and the glass transition Food Research International 28 591 597 Brake N C and OR Fennema 1993 Edible coatings to inhibit lipid migration in a confectionery product Journal of Food Science 58 1422 1425 Dole M and L Faller 1950 Water sorption by synthetic high polymers Journal of the American Chemical Society 12414 419 Fernandez Salguero J R G mez and MA Carmona 1993 Water activity in selected high moisture foods Journal of Food Composition and Analysis 6 364 369 Lomauro CJ AS Bakshi and
59. turated solutions can exist in different states and result in uncertainty in the water activity values Verification Standard W ater Activity 5M KCl 0 983 0 003 6M NaCl 0 760 0 003 8 5M LiCl 0 500 0 003 13 3M LiCl 0 250 0 003 17 AquaLab Linear O ffset and Verification Standards If for some reason you cannot obtain Decagon s verification standards and need to make a saturated salt solution for verification refer to Appendix A W hen to Verify for Linear Offset Linear offset should be checked against a known verification standard on a frequent if not daily basis Linear offset should never be adjusted when measuring distilled water since it does not give an accurate representation of the linear offset For batch processing the instrument should be checked regularly against a known standard of similar a It is also a good idea to check the offset with a standard of similar a when the general water activity range of your sample is changing Checking the a of a standard solution will alert you to the possibility of contamination of the unit or shifts in the linear offset from other causes How to Verify and Adjust for Linear Offset To verify for linear offset of your AquaLab do the following 1 Choose a verification standard that is close to the ay of the sample you are measuring Each of the verification stan dards supplied by Decagon has its ay labeled Before you begin sa
60. uncertainty he published is due to variation among the results from the different methods There are therefore limitations to the accuracy of these values The instrumentation available for making water activity measurements is much better now than it was in 1977 so improved standards are needed Saturated salt solutions can be prepared by several methods The AOAC method involves starting with salt and adding water in small increments stirring well with a spatula after each addition until salt can absorb no more water as evidenced by free liquid where it will take on the shape of the container but will not easily pour This method gives the most accurate readings but only for a short time unless great care is taken to 15 AquaLab Linear O ffset and Verification Standards prevent water gain or loss When a salt standard is prepared so that it consists mostly of liquid with a few crystals in the bottom it can result in a layer of less than saturated solution at the surface which will produce a higher reading than anticipated Conversely solid crystals protruding above the surface of the liquid can lower the readings To comply with Good Laboratory Practices GLP a saturated salt solution must read within reasonable analytical error of the accepted published value for a given temperature A qualab s Verification Standards Our research indicates that unsaturated salt solutions make much better standards than saturated sa
61. wever a limited number of loaner instruments They are granted on a first come first served basis This service is in place to help you if your AquaLab needs service during critical operations 50 AquaLab Troubleshooting P 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 Here is a list of some problems you may occur as well as an explanation of the error messages your instrument may give you If you have encountered a problem that isn t addressed here or if these remedies still don t resolve your problem contact Decagon at 1 800 755 2751 or 509 332 2756 for those not in the US or Canada Problems and Solutions PROBLEM AquaLab won t turn on SOLUTION e Check to make sure your power cord is securely attached the back of the instrument and into the power outlet A power surge may have caused a fuse to blow To change the fuses follow these instructions l Unplug the power cord from the wall and the instrument 51 AquaLab Troubleshooting 2 Locate the panel where the power cord plugs in The fuse box is on the right side of that panel Press in on the release tab and pull the fuse holder out 3 Pull the broken fuse s out and replace with a 1Amp 250V fast blow fuse Caution Do not use any other
62. y cause the sample material to spill and contaminate the sample chamber e Take special care not to move the sample drawer too quickly when loading liquid samples in order to avoid spilling f asample has a temperature that is four degrees higher or more than the AquaLab s chamber the instrument will alert you to cool the sample before reading Although the instru ment will measure warmer samples the readings may be inaccurate e The physical temperature of the instrument should be between 5 43 C Between these ambient temperatures AquaLab will measure samples of similar temperature 27 AquaLab Taking a Reading quickly and accurately AquaLab model CX 2T has tempera ture control capabilities that enable it to read samples at temperatures different from ambient temperature but no higher than 43 C If a sample has an a of lower than 03 AquaLab s display will read LO to notify you that your reading is too low If you know that your sample s water activity is above 03 and you still get the LO message your instrument s sensors have probably been contaminated and will need to be cleaned or serviced Please refer to Chapter 11 for more infor mation A reading of LO is also displayed if the instrument has not detected the formation of dew on the mirror during one complete read cycle This is an indication of contamination and the instrument should be cleaned To measure powdery samples ta
63. y mailing in the postage paid card Please include all of the information requested on the warranty card It is necessary for Decagon to have your current mailing address and telephone number in case we need to send updated product information to you Note to our AquaLab Users We understand that some of our references to scientific terminology in this manual may not meet the criteria of some members of the scientific community We apologize for this However this manual is written to aid the end user in understanding the basic concepts and theories of water activity enabling them to use our instrument with confidence Every effort has been made to ensure that the content of this manual is correct and scientifically sound Seller s Liability Seller warrants new equipment of its own manufacture against defective workmanship and materials for a period of one year 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 but Seller s liability for defective parts shall in no event exceed the furnishing of replacement parts F O B the factory where originally manufactured Material and equipment covered hereby which is not manufactured by Seller shall be covered only by the warranty of its manufacturer Seller shall not be AquaLab Introduction liable to Buyer for loss damage or injuries to pers
64. you are trying to read may be too dry for the AquaLab to make an accurate measurement The mirror may be dirty Refer to Chapter 10 for instruc 54 AquaLab Troubleshooting tions on cleaning e Your AquaLab s optical sensor may not be detecting the for mation of of dew on the mirror Refer to Chapter 10 for instructions on cleaning e One of the chamber components may be damaged Contact Decagon for details PROBLEM The potentiometer twists all the way around making it difficult or impossible to adjust for a linear offset SOLUTION e Do not force the potentiometer It was designed to only rotate one full turn If you can twist it all the way around it is broken and your AquaLab must be returned for repair See Chapter 11 for repair instructions PROBLEM While using AquaLab at elevated temperatures the instrument displays Zeroes or garbage on the screen SOLUTION The water bath or environmental temperature is above 40 C Cool the water bath and lower the environmental temperature AquaLab will not be damaged by these higher temperatures If the problem persists after cooling carefully clean the block If this doesn t solve the problem please contact Decagon for technical assistance at 4800 755 2751 or aqualab decagon com 55 AquaLab Further Reading B Further Reading Sa Ti Water Activity Theory and Measurement Bousquet Ricard M G Qualyle T Pharm and J C Cheftel 19

AquaLabCX-2v3 AquaLab CX

Contents

Download Pdf Manuals

Related Search

Related Contents