MFHPB-18 Determination of the Aerobic Colony Count in Foods
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C31D26D0CC2B4A5792634BF790EE5563 |
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0.03 |
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6 |
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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/food-aliment,Government of Canada Gouvernement du Canada,HPB Method MFHPB-18,October 2001,HEALTH PRODUCTS AND FOOD BRANCH,OTTAWA,DETERMINATION OF THE AEROBIC COLONY COUNT IN FOODS,Microbiology Evaluation Division,Bureau of Microbial Hazards, HPFB,Postal Locator 2204A1,Ottawa, Ont. K1A 0L2,1. APPLICATION,This method is applicable to the enumeration of viable aerobic bacteria (psychrophilic, mesophilic and/or,thermophilic bacteria) in foods, to determine compliance with the requirements of Sections 4 and 7 of the,Food and Drugs Act. Where an Official Method for a food is specified, that method shall be followed. This,revised method replaces MFHPB-18, dated April 1998.,2. PRINCIPLE,The Aerobic Colony Count (ACC) estimates the number of viable aerobic bacteria per g or mL of product.,A portion of the product is mixed with a specified agar medium and incubated under specific conditions of,time and temperature. It is assumed that each viable aerobic bacterium will multiply under these conditions,and give rise to a visible colony which can be counted.,3. DEFINITION OF TERMS,See Appendix A of Volume 2.,Psychrophilic bacteria: an organism which grows optimally at or below 15°C, which has an upper limit for,growth at ca. 20°C, and which has a lower limit of growth of 0°C or lower.,Mesophilic bacteria: an organism whose optimim growth temperature lies within a range generally accepted,as ca. 20 - 45°C.,Thermophilic bacteria: an organism whose optimimum growth temperature is > 45°C. See MFHPB-01.,4. COLLECTION OF SAMPLES,See Appendix B of Volume 2.,MFHPB-18,October 2001,-2-,5. MATERIALS AND SPECIAL EQUIPMENT,The following media and reagents (1-4) are commercially available and are to be prepared and sterilized,according to the manufacturer's instructions. See also Appendix G of Volume 2 for the formula of individual,media.,1) Plate count agar (PC),2) Peptone water diluent (0.1%)(PW),3) 2% sodium citrate (tempered to 450C) (for cheese samples only),4) Sodium 2,3,5 triphenyltetrazolium chloride (0.1%) (optional),5) 1N HCl and 1N NaOH,6) pH meter or paper capable of distinguishing to 0.3 to 0.5 pH units within a range of 5.0 to 8.0,7) Stomacher, blender or equivalent,8) Incubator capable of maintaining the growth temperature required for the specific type of aerobic,bacteria being enumerated (i.e. for psychrophilic bacteria: 15 - 20°C, for mesophilic bacteria: 30 -,35°C, and for thermophilic bacteria: 55°C) and 45oC waterbath,NOTE: It is the responsibility of each laboratory to ensure that the temperature of the incubators or waterbaths are,maintained at the recommended temperatures. Where 35EC is recommended in the text of the method, the,incubator may be 35 +/-1.0EC. Similarly, lower temperatures of 30 or 25°C may be +/- 1.0EC. However,where higher temperatures are recommended, such as 43 or 45.5EC, it is imperative that the incubators or,waterbaths be maintained within 0.5EC due to potential lethality of higher temperatures on the microorganism,being isolated.,9) Colony counting device (optional),6. PROCEDURE,Determine which type of aerobic bacteria are being enumerated. Analyze each sample unit individually.,The test shall be carried out in accordance with the following instructions:,6.1 Handling of Sample Units,6.1.1 During storage and transport, the following shall apply: with the exception of shelf-stable,products, keep the sample units refrigerated (0-5oC). Sample units of frozen products shall,be kept frozen.,6.1.2 Thaw frozen samples in a refrigerator or under time and temperature conditions which,prevent microbial growth or death.,6.1.3 Analyze sample units as soon as possible after receipt in the laboratory.,6.2 Preparation of Media,6.2.1 Prepare plate count agar and dispense in appropriate quantities. Sterilize.,6.2.2 Temper prepared melted agar in a waterbath to 45oC ensuring that the water level is 1 cm,above the level of the medium in the bottles.,6.2.3 Clean surface of working area with a suitable disinfectant.,MFHPB-18,October 2001,-3-,6.2.4 Clearly mark the duplicate Petri plates.,6.3 Preparation of Dilutions,6.3.1 Prepare sterile 0.1% peptone water diluent.,6.3.2 To ensure a truly representative analytical unit, agitate liquid or free flowing materials until,the contents are homogeneous. If the sample unit is a solid, obtain the analytical unit by,taking a portion from several locations within the sample unit.,6.3.3 Prepare a 1:10 dilution of the food by aseptically blending 25 g or mL (the analytical unit),into 225 mL of the required diluent, as indicated in Table I. If a sample si……
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