MFLP-66 Determination of Water Activity Using the Decagon Aqualab CX-2 and Series 3
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2D7DC94D9FB5480385B3130888B68500 |
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0.03 |
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页数： |
8 |
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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-66,June 2006,HEALTH PRODUCTS AND FOOD BRANCH,OTTAWA,DETERMINATION OF WATER ACTIVITY USING THE DECAGON AQUALAB CX-2 AND SERIES 3,Patti Wilson,Canadian Food Inspection Agency,Atlantic Region,P.O. Box 1060,Dartmouth, Nova Scotia,B2Y 3Z7,wilsonpa@inspection.gc.ca,Irene Iugovaz,Food Directorate,Health Canada-Quebec Region,1001 St-Laurent west,Longueuil, Quebec,J4K 1C7,irene_iugovaz@hc-sc.gc.ca,1. APPLICATION,This method is applicable to the measurement of water activity in foods and food ingredients to,determine compliance with the requirements of Sections 4 and 7 of the Food and Drugs Act,Section B.27.001 of the regulations of the Food and Drugs Act and any other federal regulation.,This revised method replaces MFLP-66, dated October 2001.,2. PRINCIPLE,Water activity plays an important role in the preservation of food and the control of microbial,growth, especially pathogens. Decagon AquaLab models CX-2 and Series 3 use the chilled-mirror,dewpoint technique to measure the water activity of a product.,3. DEFINITION OF TERMS,See Appendix A of Volume 3, items 1,2,3,4.,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.,Equilibration: When the aw values of any two readings are less than .001 apart, the instrument,has reached equilibrium and the measurement process stops.,MFLP-66,- 2 - June 2006,Humidity standard (slush) : is a saturated solution of a salt of a known % relative humidity at a,designated temperature.,Commercial humidity standard: is an unsaturated salt solution of a specific molality representing a,know Aw.,4. COLLECTION OF SAMPLES,See Appendix B of Volume 3.,Keep samples sealed to prevent loss or gain of moisture during transport.,5. APPARATUS AND MATERIALS,5.1 Apparatus,5.1.1 AquaLab Models CX-2 and Series 3 are available from Decagon Devices Inc., P.O.Box,835, 950 NE Nelson Court, Pullman, Washington USA 99163. The Canadian distributor is,Meyer Service and Supply Ltd., 119 Warner Drive RR1 Long Sault, Ont. K0C 1P0.,5.2 Materials,5.2.1 Reference salts: ACS reagent grade, fine crystal, available from scientific supply houses.,See Table 1 for a list of the reference salts which may be used.,5.2.2 Reference humidity standards, available from Decagon distributors.,5.2.3 Disposable sample cups from Decagon or equivalent.,5.2.4 Test containers - 120 mL or 240mL Mason-type glass jar with screw-caps and gaskets or,equilavent,5.2.5 AquaLab cleaning kit (optional),6. PROCEDURE,Each sample unit may be analyzed individually or the analytical units may be combined. Carry out,the test in accordance with the following instructions:,6.1 Handling of Samples Units,6.1.1 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 microbial growth or,death. Maintain package integrity until the point of measurement to prevent water loss,which may alter the water activity.,6.1.2 Analyze sample units as soon as possible after their receipt in the laboratory.,6.2 Reference Humidity Standards,6.2.1 Certified humidity standards are preferred and may be purchased.,MFLP-66,- 3 - June 2006,6.2.2 To prepare in-house reference humidity standards, place selected reference salt in a,labeled test container to a depth of about 4 cm. Add distilled water in gradual increments,with constant stirring until no more water is absorbed and there is some free liquid on top,of the slush. At this point they are ready to use and will keep indefinitely, if contained in,manner to prevent substantial evaporation losses.,6.2.3 To use the in-house reference humidity standard for the AquaLab, use the liquid portion,of the mixture only.,6.2.4 Replace either of the purchased or in-house humidity standards if they become,contaminated or expired.,QUALITY CONTROL,The aw reading obtained by measuring the Decagon Devices humidity standards must be,within ±0.003 aw units of the stated value of the standard.,To determine the accuracy of uncertified humidity standards, use a method that is independent,of the calibration methodology in order to have a meaningful check on the standard material.,Options include:,1. Send blind samples to another facility to be checked on the same type of aw apparatus.,2. Test blind samples on a type of apparatus diff……
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