ISO 17410:2019 pdf free

ISO 17410:2019 pdf free.Microbiology of the food chain – Horizontal method for the enumeration of psychrotrophic microorganisms
To detect low microbial counts, the limit of detection may be increased by a factor of 10 by analysing 1,0 ml of the test sample (liquid product) or 1,0 ml of the initial suspension (non-liquid product). This is achieved by spreading 1,0 ml of the inoculum either over the surface of one large Petri dish (140 mm diameter) or over the surface of three small Petri dishes (90 mm diameter). If two plates per dilution are needed, prepare them using two large ones or six small ones.
Take one other Petri dish (6.5) containing the plate count agar medium (see A.3). Use another sterile pipette (6.8) to dispense 0,1 ml of the next decimal dilution (the colonies to be counted will then be present in a dilution step of 10-1 in the case of liquid products and 10-2 in the case of non-liquid products).
Using a spreader or spatula (6.2), carefully spread the inoculum evenly over the agar surface as quickly as possible after dispensing without touching the sidewalls of the Petri dish (6.5). Allow the inoculum to be absorbed by the agar with the lids on for approximately 15 min at room temperature and check if the agar surface is dry before incubation.
Following the period of incubation (see 9.2.5), count the colonies from the first (lowest) dilution with no more than 150 colonies. Count the colonies on the plates using the colony-counting device (6.1),if necessary. Examine the plates under subdued light. It is important that pinpoint colonies are included in the count; however, it is essential that the operator avoids mistaking particles of undissolved or precipitated matter in the plates for pinpoint colonies. Examine doubtful objects carefully, using higher magnification where required, in order to distinguish colonies from foreign matter.
Consider spreading colonies or a chain of overlapping or at least connected colonies as single colonies. If less than one-quarter of the plate is covered by spreading growth, count the colonies on the unaffected part and calculate the theoretical number for the entire plate by extrapolation. Discard the count if more than one-quarter is overgrown.ISO 17410 pdf free download.