AOAC Official Method 996
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4594C043865E473A9F83DABCA87D0035 |
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0.03 |
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3 |
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日期： |
2024-7-30 |
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17.3.03A,AOAC Official Method 996.02,Coliform Count,in Dairy Products,High-Sensitivity Dry Rehydratable Film Method,First Action 1996,Revised First Action 1999,(Applicable to determination of low levels of coliform bacteria in,dairy products. See Table 996.02A for the results of the,interlaboratory study supporting the acceptance of the method. See,Table 996.02B for comparison of the modified Petrifilm?HSCC,plate method to the original Petrifilm HSCC plate method and the,VRBA method for enumeration of coliforms at low, medium, and,high levels of inoculation. See Table 996.02C for repeatability standard,deviations of the modified Petrifilm HSCC plate and the original,Petrifilm HSCC plate methods.),A. Principle,Undiluted or diluted test portions are added to plates of dry medium,and cold H2O-soluble gel at a rate of 5.0 mL/plate. Pressure,when applied to plastic spreader placed on overlay film, spreads test,suspensions over ca 60 cm2 growth area. Gelling agent is allowed to,solidify, plates are incubated, and coliforms are counted.,B. Apparatus and Reagent,(a) High-Sensitivity Coliform Count Plates?.—Plates contain,modified violet red bile, cold H2O-soluble gelling agent, and,2,3,5-triphenyltetrazolium chloride indicator. Petrifilm,High-Sensitivity Coliform Count Plates (available from 3M Microbiological,Products, 3M Center Building, 275-5W-05, St. Paul,MN,55144, USA, No. 6405) or equivalent product producing similar,method performance statistics meet these specifications.,(b) Plastic spreader.—Provided with Petrifilm plates; designed,to spread test portion evenly over plate growth area.,(c) Pipets.—Calibrated for bacteriological use. Automatic pipet,to deliver 5.0 mL may be used.,(d) Colony counter.—Standard apparatus, Quebec model preferred,(Fisher Laboratory Products, 200 Park Ln, Pittsburgh,PA15275, USA, No. 07-908-7), or one providing equivalent magnification,(1.5′) and visibility.,(e) Dilution water.—Prepare stock solution as follows: Dissolve,34 g KH2PO4 in 500 mL H2O, adjust to pH 7.2 with 1M NaOH,(40g/L; ca 175 mL), and dilute to 1 L with H2O. Prepare buffered,H2O for dilutions by diluting 1.25 mL stock solution to 1 L with,boiled and cooled H2O. Autoclave 15 min at 121°C.,(f) Stomacherò lab blender.,. 2002 AOAC INTERNATIONAL,Table 996.02A Interlaboratory study results for determination of coliform in dairy products by high-sensitivity dry rehydratable,film method,Product Level,Mean log,cfu/g sr sR RSDr, % RSDR, % ra Rb,2% milk Low 0.681 0.058 0.101 8.4 14.9 0.162 0.283,Medium 1.576 0.067 0.082 4.3 5.2 0.188 0.230,High 2.437 0.071 0.109 2.9 4.5 0.199 0.305,Chocolate milk Low 0.612 0.241 0.241 39.4 39.4 0.675 0.675,Medium 1.637 0.088 0.090 5.4 5.5 0.246 0.252,High 2.607 0.114 0.116 4.4 4.5 0.319 0.325,Cream Low 0.638 0.255 0.255 39.9 39.9 0.714 0.714,Medium 1.661 0.046 0.071 2.8 4.3 0.129 0.199,High 2.679 0.081 0.095 3.0 3.5 0.227 0.266,Vanilla ice cream Low 0.147 0.203 0.208 138.1 141.2 0.568 0.582,Medium 1.098 0.146 0.178 13.3 16.2 0.409 0.498,High 1.899 0.087 0.170 4.6 9.0 0.244 0.476,Cottage cheese Low 1.420 0.139 0.185 9.8 13.0 0.389 0.518,Medium 2.410 0.112 0.131 4.7 5.4 0.314 0.367,High 3.361 0.115 0.125 3.4 3.7 0.322 0.35,Cheddar cheese Low 0.311 0.055 0.055 17.7 17.7 0.154 0.154,Medium 1.633 0.105 0.180 6.4 11.0 0.294 0.504,High 3.122 0.071 0.226 2.3 7.2 0.199 0.633,a r = 2.8 ′ sr.,b R = 2.8 ′ sR.,. 2002 AOAC INTERNATIONAL,Table 996.02B Comparison of the modified Petrifilm HSCC plate method to the original Petrifilm HSCC plate method and the VRBA,method for enumeration of coliforms at low, medium and high levels of inoculation.,Food log mHSCC – log HSCCa log mHSCC – log VRBAb,N,Mean log,difference T-value p-value N,Mean log,difference T-value p-value,Low level of inoculation,Butter 8 0.109 0.832 0.433 8 –0.228 –1.082 0.315,Buttermilk 9 –0.039 –0.277 0.789 9 –0.146 –1.275 0.238,Cheese 10 –0.026 –0.356 0.730 10 0.124 1.521 0.163,Chocolate milk 7 0.014 0.306 0.770 8 –0.111 –0.787 0.457,Cream 10 0.094 1.183 0.267 10 0.136 3.092 0.013c,Frozen yogurt 10 0.170 2.603 0.029c 9 0.102 0.880 0.405,Ice cream 10 0.052 0.906 0.388 9 0.136 1.836 0.104,Sour cream 8 –0.055 –0.368 0.724 8 –0.379 –2.155 0.068,Sweetened condensed milk 7 –0.106 –1.032 0.342 7 –0.301 –2.537 0.044c,Whole milk 10 0.030 0.789 0.450 10 0.428 4.570 0.001c,All foods 89 0.029 1.013 0.314 88 –0.001 –0.029 0.977,Medium level of inoculation,Butter 10 0.048 0.516 0.617 10 –0.317 –2.580 0.030c,Buttermilk 10 0.048 0.638 0.539 10 –0.150 2.330 0.045c,Cheese 10 –0.035 –0.658 0.527 10 0.131 2.072 0.068,Chocolate milk 8 –0.097 –1.098 0.308 8 –0.136 –3.042 0.019c,Cream 10 0.024 0.699 0.502 10 0.048 0.649 0.532,Frozen……
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