GB 4789.2-2022 PDF EnglishUS$105.00 · In stock · Download in 9 seconds
GB 4789.2-2022: National food safety standard - Microbiological examination of food: Aerobic plate count Delivery: 9 seconds. True-PDF full-copy in English & invoice will be downloaded + auto-delivered via email. See step-by-step procedure Status: Valid GB 4789.2: Historical versions
Similar standardsGB 4789.2-2022: National food safety standard - Microbiological examination of food: Aerobic plate count---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GB4789.2-2022 NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA National food safety standard - Microbiological examination of food. Aerobic plate count Issued on. JUNE 30, 2022 Implemented on. DECEMBER 30, 2022 Issued by. National Health Commission of the PRC; State Administration for Market Regulation. Table of ContentsForeword... 3 1 Scope... 4 2 Terms and definitions... 4 3 Equipment and materials... 4 4 Medium and reagents... 5 5 Examination procedure... 5 6 Operation steps... 6 7 Result and report... 8 Appendix A Medium and reagents... 10 Appendix B Examples... 12ForewordThis Standard replaces GB 4789.2-2016 "National food safety standard - Food microbiological examination - Aerobic plate count". Compared with GB 4789.2-2016, the main changes of this Standard are as follows. - Add Appendix B; - Modify the equipment and materials; - Modify the medium and reagents; - Modify the examination procedure; - Modify the operation steps; - Modify Appendix A. National food safety standard - Microbiological examination of food. Aerobic plate count1 ScopeThis Standard specifies the method for the determination of aerobic plate count in food. This Standard applies to the determination of aerobic plate count in food.2 Terms and definitions2.1 Aerobic plate count The total number of microbiological colonies formed in per g (mL) of test sample, which is obtained after the food sample under test is processed and cultured under certain conditions (such as culture medium, culture temperature, and incubation time, etc.).3 Equipment and materialsIn addition to the routine sterilization and culture equipment in the microbiology laboratory, other equipment and materials are as follows. a) Constant-temperature incubator. b) Refrigerator. c) Thermostat. d) Balance. Sensitivity is 0.1 g. e) Homogenizer. f) Oscillator. g) Sterile straw. 1 mL (with 0.01 mL scale), 10 mL (with 0.1 mL scale) or micropipette and tip. h) Sterile conical flask. Capacity is 250 mL and 500 mL. i) Sterile petri dish. Diameter is 90 mm. j) pH meter or pH colorimetric tube or precision pH test paper. k) Magnifying glass or/and colony counter.4 Medium and reagents4.1 Plate count agar medium. See A.1. 4.2 Test piece of aerobic plate count. It shall meet the quality control requirements of plate count agar medium in GB 4789.28.The main nutrients are consistent with the formula of plate count agar medium. 4.3 Sterile phosphate buffer. See A.2.5 Examination procedureThe examination procedure for aerobic plate count is shown in Figure 1.6 Operation steps6.1 Dilution of sample 6.1.1 Solid and semi-solid sample. Weigh 25 g of sample; place it in a sterile homogeneous cup filled with 225 mL of sterile phosphate buffer or sterile normal saline. Homogenize at 8000 r/min~10000 r/min for 1 min~2 min. Or put it into a sterile homogeneous bag containing 225 mL of diluent. Use a slap-type homogenizer to beat for 1 min~2 min, to make a 1.10 sample homogenate. Test sample25 g (mL) of sample + 225 mL of diluent,homogenized10-fold serial dilution Culture Add 15 mL~20 mL of plate count agar medium to each dish and mix well Select 1~3 sample homogenates of appropriate dilution; add 1 mL of each to asterile petri dish Count the number of colonies on each plate Calculate the aerobic plate count Report Culture at 36 °C±1 °C for 48 h±2 h. Aquatic products are cultured at 30 °C±1 °C for 72 h±3 h 6.1.2 Liquid sample. Use a sterile straw to pipette 25 mL of sample; place it in a sterile conical flask containing 225 mL of sterile phosphate buffer or sterile normal saline (an appropriate number of sterile glass beads can be preset in the bottle); and mix thoroughly. Or put it into a sterile homogeneous bag containing 225 mL of diluent. Use a slap-type homogenizer to beat for 1 min~2 min, to make a 1.10 sample homogenate. When the result is required to be the aerobic plate count per g of sample, operate according to 6.1.1. 6.1.3 Use a 1 mL sterile straw or micropipette to draw 1 mL of the 1.10 sample homogenate; along the tube wall, slowly inject it into a sterile test tube containing 9 mL of diluent (be careful not to touch the surface of the diluent with the pipette or the tip). Oscillate and mix on an oscillator, to make a 1.100 sample homogenate. 6.1.4 According to the operation in 6.1.3, prepare a 10-fold serial dilution of the sample homogenate. For each incremental dilution, use a new 1 mL sterile straw or tip. 6.1.5 According to the estimation of the contamination status of sample, select 1 to 3 sample homogenates with appropriate dilution (liquid samples can include stock solution). Pipette 1 mL of the sample homogenate into a sterile petri dish; make two petri dishes for each degree of dilution. At the same time, respectively pipette 1 mL of blank diluent; add it to two sterile petri dishes as blank control. 6.1.6 In a timely manner, pour 15 mL~20 mL of plate count agar medium cooled to 46 °C~50 °C (which can be kept in a thermostat at 48 °C±2 °C) into a petri dish; rotate the petri dish to make it evenly mixed. 6.2 Culture 6.2.1 Place horizontally until the agar solidifies; turn the plate over; incubate at 36 °C±1 °C for 48 h±2 h. Aquatic products are cultured at 30 °C±1 °C for 72 h±3 h. If the sample may contain colonies that spread and grow on the surface of the agar medium, it is possible to cover the surface of the solidified agar medium with a thin layer of plate count agar medium (about 4 mL). After solidification, turn the plate over and culture. 6.2.2 If the test piece of aerobic plate count is used, it shall be operated in accordance with the relevant technical regulations provided for the test piece. 6.3 Colony count 6.3.3 When one of the plates has larger flaky colonies, it is not suitable to use it. The plate without larger flaky colonies shall be used as the colony count of the degree of dilution. If the flaky colonies are less than half of the plate, and the colonies in the remaining half are evenly distributed, it is possible to calculate the number of the half plate and multiply it by 2, to represent the number of colonies on one plate. 6.3.4 When there is a chain growth with no clear boundary between the colonies on the plate, count each single chain as a colony.7 Result and report7.1 Calculation method of aerobic plate count 7.1.1 If the number of colonies on only one dilution plate is within the appropriate count range, calculate the average of the number of colonies on the two plates; then multiply the average by the corresponding dilution factor as the aerobic plate count per g (mL) of the sample. Example is given in B.1. 7.1.2 If the number of colonies on the plate with two serial dilutions is within the appropriate count range, calculate according to formula (1). For an example, see B.2. Where. 7.1.3 If the number of colonies on all dilution plates is greater than 300 CFU, the plate with the highest dilution shall be counted. The other plates can be recorded as uncountable. The result shall be calculated by multiplying the average number of colonies by the highest dilution ratio. For an example, see B.3. 7.1.4 If the plate colony count of all dilutions is less than 30 CFU, it shall be calculated by multiplying the average colony count with the lowest dilution by the dilution ratio. For an example, see B.4. 7.1.5 If plates at all degrees of dilution (including liquid sample stock solution) have no colony growth, it shall be calculated by multiplying less than 1 by the minimum dilution ratio. For an example, see B.5. 7.1.6 If the number of colonies on the plates at all degrees of dilution is not between 30 CFU and 300 CFU, and some of them are less than 30 CFU or greater than 300 CFU, it shall be calculated by multiplying the average colony number closest to 30 CFU or 300 CFU by the dilution ratio. For an example, see B.6. 7.2 Report of aerobic plate countAppendix AMedium and reagents A.1 Plate count agar (PCA) medium A.1.1 Ingredients Tryptone (main nutrient). 5.0 g Yeast extract (main nutrient). 2.5 g Glucose (main nutrient). 1.0 g Agar. 15.0 g Distilled water. 1000 mL A.1.2 Preparation method Add the above ingredients to distilled water; boil to dissolve; adjust the pH to 7.0±0.2. Dispense into suitable containers; sterilize by autoclaving at 121 °C for 15 min. A.2 Sterile phosphate buffer A.2.1 Ingredients Potassium dihydrogen phosphate (KH2PO4). 34.0 g Distilled water. 500 mL A.2.2 Preparation method Stock solution. Weigh 34.0 g of potassium dihydrogen phosphate and dissolve it in 500 mL of distilled water; use about 175 mL of 1 mol/L sodium hydroxide solution to adjust the pH to 7.2; use distilled water to dilute to 1000 mL; store in the refrigerator. Diluent. Take 1.25 mL of the stock solution; use distilled water to dilute to 1000 mL; divide it into suitable containers; sterilize it by autoclaving at 121 °C for 15 min. A.3 Sterile normal saline A.3.1 Ingredients Sodium chloride. 8.5 g Distilled water. 1000 mL A.3.2 Preparation method Weigh 8.5 g of sodium chloride; dissolve it in 1000 mL of distilled water; sterilize by autoclaving at 121 °C for 15 min. ......Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al. 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