ISO 6887-5:2020 pdf download – Microbiology of the food chain —Preparation of test samples, initialsuspension and decimal dilutions formicrobiological examination — Part 5: Specific rules for the preparation of milk and milk products.
8.3 Hard and dry products
To mix hard products in a peristaltic blender, place the sample and diluent in double- or triple-layered sterile bags to prevent puncturing and possible sample spillage, or alternately homogenize using a rotary blender when appropriate for hard, low moisture products.
Follow ISO 6887-1 for alternative preparation methods.
8.4 Liquid and non-viscous products Follow ISO 6887-1.
8.5 Multi-component products Follow ISO 6887-1.
8.6 Acidic products Follow ISO 6887-1.
8.7 High-fat foods (fat content> 20 % mass fraction) Follow ISO 6887-I.
9 Specific procedures
9.1 Milk and liquid milk products
Mix the test sample thoroughly so that the microorganisms are distributed as evenly as possible by rapidly inverting the sample contaIner 25 tImes. Avoid foaming or allow any foam to disperse. The interval between mixing and removing the test portion shall not exceed 3 mm.
Remove the test sample with a sterile pipette and prepare further dilutions in accordance with ISO 6887-1 or inoculate directly a medium or a broth in accordance with the procedure of the specific meLhod of enumeration or detection.
9.2 Dehydrated milk, dehydrated sweet whey, dehydrated acid whey, dehydrated buttermilk and lactose
Thoroughly mix the contents of the closed container by repeatedly shaking and inverting it.
If the test sample is in the original unopened container and this is too full to permit thorough mixing. transfer it to a larger container, then mix. Open the container, remove the test portion required with a spatula 16.2) and proceed as Indicated below. Immediately close the container again.
Prepare the initial suspension in accordance with ISO 6887-1 for dehydrated products and other low- moisture products, with a diluent for general use (&L2). For dehydrated acid whey. use dipotassium hydrogen phosphate solution (5.1,3.2) at pH 8,4 ± 0,2 or. if necessary, for roller-dried milk use sodium citrate solution (5.L3.i) or dipotassium hydrogen phosphate solution (513.2) at pH 7,5 ± 0,2.
NOTE For better reconstitution and In p.ilcular with roller-dried milk, glass beads (6.4) can be helpful. II used, they are added to the bottle before sterilization.
Swirl slowly until the test portion has dispersed completely. Allow to stand for S mm, swirling occasionally.
A peristaltic blender may be used. If dispersion is not complete.
The diluent may be pre-warmed to (44 to 47) °C In a water bath 1) if a homogeneous suspension cannot he obtained even after blending. Mention such an additional procedure in the test report.
9.3 Cheese and cheese products
Weigh the test portion into the conLainr ut a rotary blender Ut via peristaltEc blender. Add a diluent for general use (51.2). sodium citrate solution (5.1.3.1) or dipotassium hydrogen phosphate solution (SLi2) at pH 7,5 , 0,2. Blend until the cheese is thoroughly dispersed. Allow any foam to disperse.
The diluent may be pre-warmed to (44 to 47) C in a water bath (f1) if a homogeneous suspension cannot 1w obtaIned even after blending. Mention such an additional procedure In the test report.
9.4 Add casein, lactic caseln, rennet caseln and caselnale
9.4.1 General case
Thoroughly mix the contents of the closed container by repeatedly shaking and inverting it.
Weigh the test portion into a sterile plasuc bag for a peristaltic blender. Add the appropriate dilucnt at room temperature, as follows:
a) for acid and lactic casein: dilute with dipotassium hydrogen phosphate solution with antifoam agent (5.1.3.3) at pH 8,4 ± 0.2:
b) for caselnate: dilute with peptone-salt solution (11.2). sodium citrate solution (51.31) or dipotassium hydrogen phosphate solution (5.1.3.2) at pH 7,5 ± 0.2;
c) for rennet casein: dilute with dipotassium hydrogen phosphate solution with antifoam agent (5.1.3.3) at pH 7.5 ± 0,2.
Mix well manually and allow to stand at room temperature for 15 mm. Blend for 2 mm In the peristaltic blender by using, if necessary, two sterile bags for granular products. Allow to stand for 5 nun.
9.4.2 Special case: Rennet casein
Rennet casein can be difficult to dissolve. An alternative procedure to that described in 9.4.1 may be used.
Using dipotasslum hydrogen phosphate solution with antifoam agent (5.1.3.3) as dilucnt for rennet caseins may not be efficient to dissolve the grains. These casein grains hamper the enumeration of microorganisms at 30 °C. Therefore, the following alternative procedure is recommended.
If necessary, grind the dry casein before taking the test portion. Transfer approximately 20 g of the test sample into a suitable container. Grind it using an apparatus with blades able to rotate at approximately 20 000 r/mln and equipped with a device that prevents the sample from heating during grindingt).