GB 4789.15-2010 English PDF

GB 4789.15-2010: National food safety standard -- Food microbiological examination: Enumeration of moulds and yeasts
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GB 4789.15-2010
GB
National Standard of the People’s Republic of China
National food safety standard
Food microbiological examination.
Enumeration of moulds and yeasts
ISSUED ON. MARCH 26, 2010
IMPLEMENTED ON. JUNE 01, 2010
Issued by. Ministry of Health of the People’s Republic of China
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Apparatuses and materials ... 4 
3 Culture medium and reagents ... 5 
4 Inspection procedure ... 5 
5 Operation steps ... 5 
6 Results and report ... 7 
Appendix A ... 9 
Appendix B ... 11 
Foreword 
This standard will replace GB/T 4789.15-2003 Microbiological examination of food
hygiene-Examination of moulds and yeasts, from the implementation date.
Compared with GB/T 4789.15-2003, the main changes of this standard are as follow.
- Modify the scope;
- Modify the inspection procedure and operation steps;
- Modify the culture medium and reagents;
- Modify the apparatus and materials;
- Modify the appendix.
This standard’s appendix A is normative; appendix B is informative.
The previous versions replaced by this standard are.
- GB 4789.15-1984, GB 4789.15-1994, GB/T 4789.15-2003.
National food safety standard
Food microbiological examination.
Enumeration of moulds and yeasts
1 Scope
This standard specifies the counting methods of moulds and yeasts in foods.
This standard applies to the counting methods of moulds and yeasts in all types of
foods.
2 Apparatuses and materials   
In addition to the conventional sterilization and cultivation apparatuses, other
apparatuses and materials are as follows.
2.1 Refrigerator. 2°C~5°C.
2.2 Thermostatic incubator. 28°C±1°C.
2.3 Homogenizer.
2.4 Thermostatic oscillator.
2.5 Microscope. 10x~100x.
2.6 Electronic balance. Sensitivity is 0.1g.
2.7 Sterile Erlenmeyer flasks. 500mL, 250mL capacity.
2.8 Sterile Jars. 500mL.
2.9 Sterile pipette. 1mL (with 0.01mL scale), 10mL (with 0.1mL scale).
2.10 Sterile petri dish. Diameter is 90mm.
2.11 Sterile test tube. 10mmx75mm.
2.12 Sterile Kraft paper bags and plastic bags.
5.2 Cultivation
After the agar is solidified, place the flat-plate upside down. Cultivate it for 5 days at
28°C±1°C. Observe and record.
5.3 Colony counts
Use naked eyes to observe. If necessary, it can use magnifier. Record every
dilution-multiple and corresponding number of moulds and yeasts. Use colony forming
units (CFU) to express.
Select the flat-plate of which the number of colony is at 10 CFU~150 CFU. According
to colony morphology, count the number of moulds and yeasts respectively. For those
that the moulds have spreaded and grown to cover the whole flat-plate, it may be
recorded as “too numerous to count”. The number of colony shall use the average of 2
flat-plates.
6 Results and report 
6.1 Calculate the average of colony number for 2 flat-plates. Multiply the average BY
corresponding dilution-multiple.
6.1.2 If all the colony number on the flat-plates are more than 150 CFU, count the
flat-plate which has the highest dilution. Record other flat-plates as “too numerous to
count”. Results shall be calculated by multiplying the highest dilution-multiple BY the
average of colony number.
6.1.3 If all the colony number in the flat-plates are less than 10 CFU, then it shall be
calculated by multiplying the dilution-multiple BY the average of colony number of
which the dilution is lowest.
6.1.4 If all the dilution flat-plates have no colony, multiply the number less than 1 BY
the lowest dilution-multiple; If it is stock solution, count by the number less than 1.
6.2 Report
6.2.1 If the number of colony is less than 100, according to the rounding rules, use the
2 significant figures to report.
6.2.2 If the number of colony is more than or equaling to 100, the first 3 figures adopt
rounding rules, then get the first 2 figures; the last digit is replaced by 0. Otherwise,
use the 10-exponential form to express; under the same rounding rules, get the 2
significant figures.
6.2.3 Weighing sampling shall use CFU/g as the unit for report. Volume sampling shall
use CFU/mL as the unit for report. Report or respectively report the number of moulds
Appendix B 
(informative)
Direct microscopic moulds counting method
The common method is Howard moulds measurement method. This method applies
to canned tomato paste.
B.1 Apparatuses and materials
B.1.1 Refractometer.
B.1.2 Microscope.
B.1.3 Howard measuring slide. special slides containing standard measuring
chamber.
B.1.4 Coverslip.
B.1.5 Micrometer. slide containing standard scale.
B.2 Operation steps
B.2.1 Preparation of test sample. Get quantitative test sample. Add distilled water to
dilute to the refractive index of 1.3447~1.3450 (that is, the concentration is
7.9%~8.8%). Keep for spare use.
B.2.2 Calibration of microscope standard vision. Adjust the standard vision of
microscope. According to 90-times~125-times of magnification, make the diameter to
be 1.382mm.
B.2.3 Smear. Clean the Howard measuring slide. Use glass rod to spread out the
prepared standard solution in measuring chamber uniformly, so as to prepare for
observation.
B.2.4 Observation. Put the prepared slide under standard vision of microscope to
observe the moulds. Usually each test sample shall be observed for 50 visions; 2
persons shall observe the same test sample.
B.2.5 Results and calculation. Under the standard vision, if the length of moulds
hypha exceeds 1/6 of standard vision (1.382mm) OR the total length of three hyphae
exceeds 1/6 of standard vision (that is, 1 scale of micrometer), it is positive (+);
otherwise, it is negative (-). Counted according to 100 visions, the number of visions
containing moulds mycelium is the vision percentage of moulds.
GB 4789.15-2010
GB
National Standard of the People’s Republic of China
National food safety standard
Food microbiological examination.
Enumeration of moulds and yeasts
ISSUED ON. MARCH 26, 2010
IMPLEMENTED ON. JUNE 01, 2010
Issued by. Ministry of Health of the People’s Republic of China
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Apparatuses and materials ... 4 
3 Culture medium and reagents ... 5 
4 Inspection procedure ... 5 
5 Operation steps ... 5 
6 Results and report ... 7 
Appendix A ... 9 
Appendix B ... 11 
Foreword 
This standard will replace GB/T 4789.15-2003 Microbiological examination of food
hygiene-Examination of moulds and yeasts, from the implementation date.
Compared with GB/T 4789.15-2003, the main changes of this standard are as follow.
- Modify the scope;
- Modify the inspection procedure and operation steps;
- Modify the culture medium and reagents;
- Modify the apparatus and materials;
- Modify the appendix.
This standard’s appendix A is normative; appendix B is informative.
The previous versions replaced by this standard are.
- GB 4789.15-1984, GB 4789.15-1994, GB/T 4789.15-2003.
National food safety standard
Food microbiological examination.
Enumeration of moulds and yeasts
1 Scope
This standard specifies the counting methods of moulds and yeasts in foods.
This standard applies to the counting methods of moulds and yeasts in all types of
foods.
2 Apparatuses and materials   
In addition to the conventional sterilization and cultivation apparatuses, other
apparatuses and materials are as follows.
2.1 Refrigerator. 2°C~5°C.
2.2 Thermostatic incubator. 28°C±1°C.
2.3 Homogenizer.
2.4 Thermostatic oscillator.
2.5 Microscope. 10x~100x.
2.6 Electronic balance. Sensitivity is 0.1g.
2.7 Sterile Erlenmeyer flasks. 500mL, 250mL capacity.
2.8 Sterile Jars. 500mL.
2.9 Sterile pipette. 1mL (with 0.01mL scale), 10mL (with 0.1mL scale).
2.10 Sterile petri dish. Diameter is 90mm.
2.11 Sterile test tube. 10mmx75mm.
2.12 Sterile Kraft paper bags and plastic bags.
5.2 Cultivation
After the agar is solidified, place the flat-plate upside down. Cultivate it for 5 days at
28°C±1°C. Observe and record.
5.3 Colony counts
Use naked eyes to observe. If necessary, it can use magnifier. Record every
dilution-multiple and corresponding number of moulds and yeasts. Use colony forming
units (CFU) to express.
Select the flat-plate of which the number of colony is at 10 CFU~150 CFU. According
to colony morphology, count the number of moulds and yeasts respectively. For those
that the moulds have spreaded and grown to cover the whole flat-plate, it may be
recorded as “too numerous to count”. The number of colony shall use the average of 2
flat-plates.
6 Results and report 
6.1 Calculate the average of colony number for 2 flat-plates. Multiply the average BY
corresponding dilution-multiple.
6.1.2 If all the colony number on the flat-plates are more than 150 CFU, count the
flat-plate which has the highest dilution. Record other flat-plates as “too numerous to
count”. Results shall be calculated by multiplying the highest dilution-multiple BY the
average of colony number.
6.1.3 If all the colony number in the flat-plates are less than 10 CFU, then it shall be
calculated by multiplying the dilution-multiple BY the average of colony number of
which the dilution is lowest.
6.1.4 If all the dilution flat-plates have no colony, multiply the number less than 1 BY
the lowest dilution-multiple; If it is stock solution, count by the number less than 1.
6.2 Report
6.2.1 If the number of colony is less than 100, according to the rounding rules, use the
2 significant figures to report.
6.2.2 If the number of colony is more than or equaling to 100, the first 3 figures adopt
rounding rules, then get the first 2 figures; the last digit is replaced by 0. Otherwise,
use the 10-exponential form to express; under the same rounding rules, get the 2
significant figures.
6.2.3 Weighing sampling shall use CFU/g as the unit for report. Volume sampling shall
use CFU/mL as the unit for report. Report or respectively report the number of moulds
Appendix B 
(informative)
Direct microscopic moulds counting method
The common method is Howard moulds measurement method. This method applies
to canned tomato paste.
B.1 Apparatuses and materials
B.1.1 Refractometer.
B.1.2 Microscope.
B.1.3 Howard measuring slide. special slides containing standard measuring
chamber.
B.1.4 Coverslip.
B.1.5 Micrometer. slide containing standard scale.
B.2 Operation steps
B.2.1 Preparation of test sample. Get quantitative test sample. Add distilled water to
dilute to the refractive index of 1.3447~1.3450 (that is, the concentration is
7.9%~8.8%). Keep for spare use.
B.2.2 Calibration of microscope standard vision. Adjust the standard vision of
microscope. According to 90-times~125-times of magnification, make the diameter to
be 1.382mm.
B.2.3 Smear. Clean the Howard measuring slide. Use glass rod to spread out the
prepared standard solution in measuring chamber uniformly, so as to prepare for
observation.
B.2.4 Observation. Put the prepared slide under standard vision of microscope to
observe the moulds. Usually each test sample shall be observed for 50 visions; 2
persons shall observe the same test sample.
B.2.5 Results and calculation. Under the standard vision, if the length of moulds
hypha exceeds 1/6 of standard vision (1.382mm) OR the total length of three hyphae
exceeds 1/6 of standard vision (that is, 1 scale of micrometer), it is positive (+);
otherwise, it is negative (-). Counted according to 100 visions, the number of visions
containing moulds mycelium is the vision percentage of moulds.