MFO-14 Microbiological Examination of Cheese
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EADDD64A5C804DA783B617450C6F9BB5 |
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文件大小(MB)： |
0.07 |
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页数： |
15 |
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日期： |
2012-3-2 |
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Government of Canada Gouvernement du Canada,Official Method MFO-14,November 30, 1983,HEALTH PROTECTION BRANCH,OTTAWA,MICROBIOLOGICAL EXAMINATION OF CHEESE,1. APPLICATION,This method shall be used for the determination of Escherichia coli and of Staphylococcus aureus in,cheese, including cheese curd but excluding cottage cheese, made from either pasteurized or,unpasteurized milk, in accordance with Section B.08.048 of the Food and Drug Regulations.,2. SAMPLING,2.1 Definition of Terms,2.1.1 Lot: A batch or production unit which may be identified by the same code. When there,is no code identification, a lot may be considered as (a) that quantity of cheese,produced under essentially the same conditions, at the same establishment and,representing no more than one day's production; or, (b) the quantity of the same variety,of cheese from one and the same manufacturer available for sampling at a fixed,location.,2.1.2 Sample: The sample units (subsamples) taken per lot for analysis.,2.1.3 Sample Unit: Usually a consumer size container of the product, and should consist of,a minimum of 100 g. A sample unit is often referred to as a subsample.,2.1.4 Analytical Unit: That amount of cheese withdrawn from the sample unit for analysis.,2.2 Collection of Samples,2.2.1 A sample, consisting of five sample units drawn at random from each lot, shall be taken.,2.2.2 Each sample unit shall consist of at least 100 g.,2.2.3 Collect original unopened containers or packages wherever possible.,2. 2.4 Employ aseptic techniques in collecting the sample units when sampling bulk cheese.,Place each collected sample unit into a separate sterile container.,2.2.5 Keep sample units refrigerated (0-5oC) during transportation.,3. PROCEDURE,Each sample unit shall be analyzed individually. The test shall be carried out in accordance with the,following instructions.,MFO-14,November 30, 1983,- 2 -,3.1 Handling of Sample Units,(1) Keep sample units refrigerated (0-5oC) prior to anlaysis.,(2) Analyze sample units as soon as possible after receipt at the laboratory.,3.2 Preparation of Media,The following media, prepared and sterilized according to the manufacturers' instructions, shall,be used:,(1) Lauryl Sulfate Tryptose (LST) broth,(2) Escherichia Coli (EC) broth,(3) Levine's Eosin Methylene Blue (EMB) agar,(4) Nutrient agar (NA),(5) IMViC media:,a. Tryptone broth,b. Buffered Glucose broth,c. Simmon's Citrate (SC) agar,(6) Baird-Parker (BP) agar,(7) Brain Heart Infusion (BHI) broth,(8) Trypticase Soy (TS) agar,(9) Blood agar (BA),(10) Toluidine Blue-DNA agar (TDA),(11) Phenol Red Carbohydrate broth,3.3 Preparation of Dilutions,3.3.1 Temper sterile aqueous 2% sodium citrate to 40-45oC, and prewarm sterile blender jars,to 40-45oC.,3.3.2 Combine portions from several locations within the sample unit, to obtain a,representative analytical unit of 11(10)* g.,3.3.3 Prepare a 1: 10 dilution of cheese by adding the analytical unit to 99(90)* mL of the,tempered sodium citrate solution in a prewarmed sterile blender jar. Blend for the,minimum time required to produce a homogeneous suspension. To prevent,overheating, blending time should not exceed 2.5 min.,3.3.4 Check the pH of the suspension. If the pH is outside the range of 5.5 to 7.6, adjust to,7.0 with either sterile NAOH or HCl.,3.3.5 Prepare succeeding dilutions as required to determine the total numbers of E. coli and,S. aureus, by transferring 11(10)* mL of the previous dilution into 99(90)* mL of 0.1%,sterile peptone water diluent. Shake all dilutions immediately prior to making transfers,to ensure uniform distribution of the microorganisms present.,* Weight and volume in brackets indicate alternative procedure for preparation of dilutions.,3.4 Determination of E. coli,3.4.1 Presumptive Coliform Test,a. The medium used is LST broth, dispensed in 10 mL volumes into tubes,containing gas vials (inverted Durham tubes).,MFO-14,November 30, 1983,- 3 -,b. Arrange LST broth tubes in rows of fives, and mark them identifying the,sample, the sample unit and the dilution to be inoculated.,c. Inoculate LST broth with a culture of E. coli known to ferment lactose and,produce gas at 45oC to serve as a positive control, incubate, and subsequently,transfer into all media used at different stages of the procedure. Set up an,uninoculated type of medium corresponding to each step in the procedure as,a negative control.,d. Inoculate each tube of a set of five tubes of single strength LST broth with 1 mL,of the 1:10 dilution (cheese homogenate; see section 3.3.3, above). Repeat for,each succeeding decimal dilution as required.,e. Mix inoculum and medium by gently shaking or rotating the ……
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