MFLP-63 Measuring Water activity (aW) Using the Novasina aW Center
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03F5E60AB15840749BB64BED21B694CC |
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文件大小(MB)： |
0.04 |
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页数： |
11 |
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日期： |
2012-3-2 |
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Published on the Food Directorate’s (Health Canada's) website at,http://www.hc-sc.gc.ca/fn-an/res-rech/analy-meth/microbio/index_e.html,Government of Canada Gouvernement du Canada,Laboratory Procedure MFLP-63,January 2006,HEALTH PRODUCTS AND FOOD BRANCH,OTTAWA,MEASURING WATER ACTIVITY (aw) USING THE NOVASINA aW CENTER,Patti Wilson,Canadian Food Inspection Agency,P.O. Box 1060,1992 Baffin St.,Dartmouth, N.S.,B2Y 3Z7,E-mail: wilsonpa@inspection.gc.ca,1. APPLICATION,This method may be used to determine the water activity (aw) of foods to determine compliance with,the requirements of Sections 4 and 7 of the Food and Drug Act. This revised method replaces MFLP-,63, dated April 1999.,2. DESCRIPTION,The Novasina aw Center consists of a measuring station and a temperature controlled aw -box with,3 sensors. Studies have shown that the Novasina aw Center produces satisfactory results for the,measurement of water activity in foods (8.2, 8.4 and 8.6).,3. PRINCIPLE,Water activity plays an important role in the preservation of food and the control of microbial growth,especially pathogens. The Novasina aw Center measures the relative equilibrium humidity in % rh,which is directly correlated with the water activity in accordance with the following formula: aw =,ERH/100.,4. DEFINITION OF TERMS,4.1 See Appendix A of Volume 3.,MFLP-63,- 2 - January 2006,4.2 water activity (aw) : is the ratio of the water vapour pressure in any food system to the water,vapour pressure of pure water at the same temperature.,4.3 equilibration: a change in the aw reading of # ± 0.001 aw in a 10 minute period.,4.4 humidity standard: is a saturated solution of a salt of a known % relative humidity at a,designated temperature.,5. COLLECTION OF SAMPLES,5.1 See Appendix B of Volume 3.,5.2 Keep samples sealed to prevent loss or gain of moisture during transport.,6. MATERIALS AND SPECIAL EQUIPMENT,Note: The Laboratory Supervisor must ensure that the analysis described in this method is carried out,in accordance with the International Standard referred to as “ISO/IEC 17025:2005 (or latest,version): General Requirements for the Competence of Testing and Calibration Laboratories”.,6.1 Novasina aw Center (available from Novasina AG, a division of Axair Ltd., Pf鋐fikon,Switzerland or JEB Controls Inc., Kirkland, QC),6.2 Novasina humidity control standards (available from Novasina AG, a division of Axair Ltd.,Pf鋐fikon, Switzerland or JEB Controls Inc., Kirkland, QC),6.3 aw disposable bowls (available from Novasina AG, a division of Axair Ltd., Pf鋐fikon,Switzerland or JEB Controls Inc., Kirkland, QC),6.4 Pre-filters (available from Novasina AG, a division of Axair Ltd., Pf鋐fikon, Switzerland or JEB,Controls Inc., Kirkland, QC).,7. PROCEDURE,7.1 Handling of Samples Units,7.1.1 In the laboratory prior to analysis, except for shelf-stable foods, keep sample units,refrigerated or frozen, depending on the nature of the product. Thaw frozen samples,in a refrigerator, or under time and temperature conditions which prevent loss of,moisture.,7.1.2 Analyse sample units as soon as possible after their receipt in the laboratory.,7.2 Calibration,7.2.1 Before calibrating prepare the Novasina by:,1) Turn the power switch on and leave the instrument for a minimum of 2,hours.,2) Set the temperature dial to 190 (25°C) and ensure that the temperature is,holding.,MFLP-63,- 3 - January 2006,3) Set the RTD-24 switches to "S".,4) Remove the pre-filter from each sensor (see Maintenance Procedures).,7.2.2 To decide which humidity standard to use for the upper and lower points, consider,the anticipated range of the sample and choose a humidity standard range which will,include this value. Only samples within the range of the upper and lower points can,be reported as a numerical value rather than > the upper point or < the lower point.,For routine analysis of food, use SAL-75 as the lower point and SAL-98 as the upper,point.,If using more than one humidity standard with the same water activity, dedicate one,humidity standard to one sensor and label it.,7.2.3 Calibration can proceed two ways: by using the built-in dummy values (see the,Novasina Operation Manual) or by using the D-Pot the procedure (see Appendix 4).,With only one D-Pot cable there will be some connecting and disconnecting to,calibrate all three sensors at the same time.,7.2.4 Adjustment of the low range is optional and should be done after the medium and,high range adjustments are made. Do this using SAL-53.,7.2.5 To check the linearity of the calibration, measure the aw of 4 humidity standards with,each sensor and calculate a regression line (see Appendix 2). The salts used should,include……
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