AS 5013.28:2009 pdf free downoad – Food microbiology Method 28: Examination of specific products—Liquid milks and creams

AS 5013.28:2009 pdf free downoad – Food microbiology Method 28: Examination of specific products—Liquid milks and creams.
(b) Mix thoroughly and, using peptone salt solution (3.2). prepare tenfold dilutions as described in the AS 5013 series.
6.5 Preparation of dilutions for cream samples only
6.5.1 Liquid cream
The procedure shall be as follows:
(a) Weigh 10.0 ±0.1 g of sample.
(b) Dilute with 90 ml. of peptone salt solution (3.2) prewarmed to about 45°C.
(c) Mix thoroughly and. using prewarmed peptone salt solution (3.2). prepare further tenfold dilutions as described in the AS 5013 series.
6.5.2 Thickened or coagulaled crca?n
[he procedure shall be as follows:
(a) Mix thoroughly by gently stirring with a spoon or spatula.
(b) Weigh 10.0 ±0.1 gof sample.
(c) Dilute with 90 ml. of 2% trisodium citrate solution prewarmed to about 45°C.
(d) Mix thoroughly and, using prewarmed peptone salt solution (3.2), prepare further tenfold dilutions as described in the AS 5013 series.
7 GENERAL TESTS
7.1 Direct microscopic count
Proceed as described in Appendix A. If necessary. dilute the cream 1:10 with water of approed quality (see AS 5013) before preparing the smear.
7.2 Specific microorganisms
Use the relevant procedures described in AS 5013 to examine for specific groups of microorganisms.
NOTE: See Clause 8 below for thermoduric bacteria.
7.3 Test for penicillin
Use the disc assa method for penicillin.
8 COUNT OF TIIERMODURIC BACTERIA IN RAW MILK AND CREAM
8.1 Laborator’ pastcuriiation
Pasteurize the sample in accordance with the following procedure and at the same time use a pilot tube containing milk or cream in which a thermometer is immersed to monitor the temperature of the sample tinder test.
NOTE: The degree of accuracy in estimating microbial numbers by this method depends on the number of microorganisms present in the milk. Ii is generally recognized that the degree of reproducibility by one operator decreases with counts of less than 500 000 per millilitre of milk. even when the technique is followed exactly.
Factors contributing to this poor reproducibility within and between operators are inaccuracies in measuring volumes, area of smear, inadequate fixing and staining, poor microscopy. irregular distribution of microorganisms, small number of fields actually counted in proportion to fields present in the smear, and eye fatigue.
A2 DEFINITIONS
For the purpose of this Standard, the definitions below apply.
A2.1 Microbial clump count
Microbial count based on groups of microorganisms which appear to be the same type: cell of like kind within 5 im of a group arc deemed to belong to that group, regardless of closeness to each other, cells of different types are deemed to be separate clumps.
A2.2 Indi’iduaI count
Microbial count of all individual cells, both within groups and in isolation.
A3 REAGENTS
A3.I Methylene blue staining solution (modification of New man Lampert Stain)
Add, gradually, 0.5 g of methylene blue chloride (certified grade) to a mixture of 56 mL
95 percent ethanol and 40 mL xylene (technical grade) in a stoppered 200 mL flask.
Dissolve by swirling the flask. Stand overnight (12 h to 24 h) under refrigeration
(0°C to 4°C). Filter through fine paper and add 4 mL glacial acetic acid to filtrate. Store in
a tightly closed bottle in a cool dark place.
WARNING: PREPARE THE STAIN UNDER AN EXHAUST HOOD TO AVOID INHALATION OF TOXIC SOLVENT FUMES.
NOTE: As this dye has limited shelf life, discard the solution if it becomes contaminated or shows signs of deterioration.