Aseptic Products Microbiology
I have a doubt concerning the results of Total Plate Count (TPC) and Yeast & Mold (Y&M) in aseptic products. Should they be 0 or is it possible to obtain other values as 10 for example?
When you say aseptic products, do you mean commercially sterile + aseptically processed? For example, shelf-stable canned food or shelf-stable broths in flexible packaging (e.g. TetraPak)? For products like these, you're rightly concerned with whether the finished good is commercially sterile or not. You should not be expecting any counts in a sterile product, but keep in mind that simple TPC testing is not the best method for verifying sterility in commercially sterile foods. A better method is incubation testing of a certain number of samples depending on the size of the production run.
It'll partially depend on which AOAC method they're using, but generally a lab is unlikely to every state 0 on the film read from these tests. Even if they can't see anything growing, telling you officially there's 0 growth can't be assured and puts them in a spot of liability. They'll generally use the <10 or <1 value as the lowest reading they can assert, and most people effectively take that as an indication of no growth observed or a clean result.
When you say aseptic products, do you mean commercially sterile + aseptically processed? For example, shelf-stable canned food or shelf-stable broths in flexible packaging (e.g. TetraPak)? For products like these, you're rightly concerned with whether the finished good is commercially sterile or not. You should not be expecting any counts in a sterile product, but keep in mind that simple TPC testing is not the best method for verifying sterility in commercially sterile foods. A better method is incubation testing of a certain number of samples depending on the size of the production run.
Thank you for the confirmation at not expect any count in a sterile product.
Any recommendations of references for the incubation test?
It'll partially depend on which AOAC method they're using, but generally a lab is unlikely to every state 0 on the film read from these tests. Even if they can't see anything growing, telling you officially there's 0 growth can't be assured and puts them in a spot of liability. They'll generally use the <10 or <1 value as the lowest reading they can assert, and most people effectively take that as an indication of no growth observed or a clean result.
Thank you for that reminder, i forgot that there is a procedure on how to express a result if no colony was observed depending on the dilution factor.
Thank you for the confirmation at not expect any count in a sterile product.
Any recommendations of references for the incubation test?
Below is a link describing the basic concept of incubation testing for commercially sterile products:
https://www.rapidmic...verage-products
In general, the process is like this:
- A representative selection of samples (entire packages of hermetically sealed product) is incubated in a controlled environment to promote bacterial growth
- Samples are then streak-plated onto agar to determine if bacteria are present in the package.
The premise is that a commercially sterile product should show no bacterial growth after the incubation period. The reason why simply performing a TPC count on un-incubated packages is not acceptable is because the bacteria population may be too low to detect in your product. Incubation is required to grow a low population into a level detectible by streak plating. Getting a "<10 cfu/ml" result on TPC testing of un-incubated samples is not an indication of sterility.
The exact parameters of your incubation testing program (number of samples taken, incubation temperature/time) will be specific to your product. It's important to speak with a process authority to help design your testing protocol. Without a well-designed testing program, it will be difficult to demonstrate that your thermal process is effective.