平板计数法-计数原则.pdfVIP

STANDARD PLATE COUNT, COLIFORM, AND SIMPLIFIED COUNT METHODS [Unless otherwise stated all tolerances are ±5%] SAMPLES 1. Laboratory sample requirements (see CP item 33 34) ________ STANDARD PLATE AND COLIFORM METHODS DILUTING SAMPLES 2. Work Area ________ a. Level plating bench not in direct sunlight ________ b. Sanitized immediately before start of plating ________ 3. Selecting Dilutions ________ a. Standard Plate Count ________ 1. Plate two decimal dilutions per sample ________ 2. Select dilutions to yield one plate with 25-250 colonies ________ a. Raw milk is normally diluted to 1:100 and 1:1000 ________ b. Finished products are normally diluted to 1:10 and 1:100 ________ c. The above are general guidelines and may have to be adjusted on a case by case basis (dilutions below 1:10 not required) ________ b. Coliform Counts ________ 1. For milk samples, 1 mL direct and/or decimal dilutions ________ 2. For all other products, distribute 10 mL of a 1:10 dilution among three plates, generally high fat and viscous products ________ 4. Identifying Plates