AS 5013.11.1:2018 pdf free.Australian Standard Food microbiology Method 11.1: Microbiology of the food chain-Preparation of test samples, initial suspension and decimal dilutions for microbiological examination- General rules for the preparation of the initial suspension and decimal dilutions (ISO 6887-1:2017, MOD).
5.2.2.2 Preparation
Dissolve the components in the water in flasks, bottles or test tubes (6.4), by heating if necessary.
Adjust the pH, if necessary, so that after sterilization, it is 7,0 ± 0,2 at 25 °C.
5.2.3 Double-strength buffered peptone water
This diluent may be necessary for high acid samples (see 8.6) and is prepared by dissolving double the quantities of a complete dehydrated medium in 1 000 ml of water and processing in the same manner.
If the diluent is prepared from individual ingredients, only double the quantities of the two buffer ingredients (marked t) are required.
5.3 Diluents for special purposes
See the specific standard or part of ISO 6887 appropriate to the product concerned.
5.4 Distribution and sterilization of the diluent
Dispense the diluent in volumes as necessary for the preparation of the initial suspensions into vessels (6.4) of appropriate capacity.
Dispense further diluent in volumes as necessary for the preparation of the (decimal or other ratio) dilutions into vessels (6.4) of appropriate capacity.
The tolerance allowable on final diluent volumes, after sterilization, shall not exceed ±2 %.
In order to enumerate several groups of microorganisms using different culture media, it may be necessary to distribute all the diluents (or some of them) in quantities greater than 9,0 ml into vessels (6.4) of appropriate size.
Stopper the vessels loosely to allow for expansion on heating.
Sterilize in the autoclave at 121 °C ± 3°C for 15 mm (see ISO 7218).
After autoclaving, check that the volumes from a proportion of the batch of diluent prepared are within the permitted tolerance of ±2 %. This may be achieved either destructively by emptying the contents of the vessels into a tared container after autoclaving or non-destructively by marking and weighing vessels positioned through the autoclave both before and after autoclaving. For small batches of less than 100 units, check at least one unit; for larger batches, check 3 % to 5 % by either method.
To ensure diluent volumes meet the permitted tolerance, autoclaving bulk volumes and dispensing the required amounts into sterile vessels aseptically may also be used.
5.5 Performance testing for diluents
Test all diluents before use, according to Table 1, by the method given in ISO 11133.
The productivity target for diluents requires that the number of colonies counted after the specified incubation time at laboratory ambient temperature (18°C to 27°C) shall be within ±30% of the number counted initially.AS 5013.11.1 pdf download.