AS 5013.28:2009 pdf free download – Food microbiology
5.1 Laboratory samples
It is assumed that the laboratory sample has been obtained and delivered to the laboratory according to the procedures set out in AS 1166. NOTE: The size of the laboratory sample taken in accordance with AS 1166 may be adjusted in order to provide a sufficient quantity for the required tests.
5.2 Storage and laboratory samples
Laboratory samples shall be stored at a temperature not exceeding 4°C, but without freezing, until tested. Testing shall commence within 24 h of sampling.
6 PREPARATION OF TEST SAMPLES
NOTE: For samples of pasteurized milk and cream to be prepared for phosphatase testing (see Clause 9), special instructions for preparation and mixing are given in AS 2300.1.10. These instructions should be followed in place of those given below.
6.1 Observation of physical condition and preparation for mixing
Observe the physical condition of the laboratory sample at the time of testing and record any abnormality. For cream samples only (except for phosphatase testing; see Note above), warm the sample to about 45°C, but not above. Proceed without delay to mixing (Clause 6.2) and the preparation of dilutions. The total time at 45°C shall not exceed 10 min.
6.4 Preparation of dilutions for liquid milks and liquid milk products only
The procedure shall be as follows:
(a) Prepare dilutions of the sample as described in AS 5013.11.1, using peptone salt solution (3.2) or other diluent as specified in the AS 5013 series.
(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 coagulated cream
The procedure shall be as follows:
(a) Mix thoroughly by gently stirring with a spoon or spatula.
(b) Weigh 10.0 ±0.1 g of 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.
Completely immerse a screw-capped glass test tube or glass McCartney bottle holding 10 mL of sample, in water maintained at 63.5 ±0.5°C in a thermostatically controlled water bath fitted with a suitable agitator. The temperature of the sample shall reach 63°C within 5 min. After a further 30 min, remove the tube or bottle from the water bath and immediately cool to 5°C or below in iced water. In placing the container in the cooling water, avoid wetting the closure but ensure that the level of the water is above the level of the milk or cream. Upon removal from the iced water, wipe the tube or bottle with a tissue.