Shelf life study - aerobic plate count
Hi everyone.
I have no background in microbiology and I need to understand some results that I just received back from the lab. The product is raw fish packaged in a oxygen permeable packaging. Has been always shipped out as 7 days shelf life.
So here is where the confusion comes in: day 4 organoleptic analysis is normal and Aerobic plate count >57,000 est CFU/g; day 5 organoleptic analysis abnormal and aerobic plate count >57,000,000 est CFU/g ... day 8 the organoleptic analysis is still abnormal, but the aerobic plate count drops to 3,000,000 CFU/g. The lactic acid bacteria starts going higher on day 5 which is 250 CFU/g. The pH is constant above 6 and the water activity 0.98.
Why the aerobic plate count differ so much from day 7 to day 8?!
I appreciate your help.
Hello,
Because your product has been sealed in air tight condition = anaerobic, your aerobic microorganisms will slowly die off. However, if condition right, some facultative microbial start to increase.
Hope this is helpful.
This is very interesting. It is true that aerobic plate count (APC) aerobic bacteria needs oxygen to survive. Permeable film does allow for transfer of oxygen but at a slower rate. Bacteria grows at a logarithmic rate thus will fight off other bacteria to survive. Some plausible reasons for your drop in count: A different sample portion was sampled. Could be possible that more flesh than skin was sampled (You will notice that most bacteria is held on the flesh of the fish) make sure the lab you're using uses a stomacher for your samples. The sample that was >57x10^6 could've been closer to the gills. Not sure your sample was a whole fish (You will also notice that bacteria loves to also grow on the gills since it is rich in blood with water nice and tucked away). A good idea is to portion off the fish and send the same portion of the fish along with the same lot to be sampled for shelf life.
This is very interesting. It is true that aerobic plate count (APC) aerobic bacteria needs oxygen to survive. Permeable film does allow for transfer of oxygen but at a slower rate. Bacteria grows at a logarithmic rate thus will fight off other bacteria to survive. Some plausible reasons for your drop in count: A different sample portion was sampled. Could be possible that more flesh than skin was sampled (You will notice that most bacteria is held on the flesh of the fish) make sure the lab you're using uses a stomacher for your samples. The sample that was >57x10^6 could've been closer to the gills. Not sure your sample was a whole fish (You will also notice that bacteria loves to also grow on the gills since it is rich in blood with water nice and tucked away). A good idea is to portion off the fish and send the same portion of the fish along with the same lot to be sampled for shelf life.
Thank you for your insight. Your answer makes a lot of sense ... the samples were from fillet skin-on (some were the tails, other the front part).
Dear Loredana,
It is not impossible that the locational musings in this thread are correct but frankly, after seeing yr opening data, i would have initially been validating the sampling / plate count procedure, eg duplicates for each sample, duplicated dilution ratios within textbook tolerances ?, ++. Technician had new glasses, new calculator ? :smile: But perhaps you did cross-check?
Or perhaps you were the analyst ? :sofa1:
I'm still wondering what the " > X est" meant ? Something to do with TNTC i suspect ?
Rgds / Charles.C
Dear Loredana,
It is not impossible that the locational musings in this thread are correct but frankly, after seeing yr opening data, i would have initially been validating the sampling / plate count procedure, eg duplicates for each sample, duplicated dilution ratios within textbook tolerances ?, ++. Technician had new glasses, new calculator ? :smile: But perhaps you did cross-check?
Or perhaps you were the analyst ? :sofa1:
I'm still wondering what the " > X est" meant ? Something to do with TNTC i suspect ?
Rgds / Charles.C
As always your answer is very interesting ... First: I wasn't the analyst (wish I was - no need to hide behind the couch :D); Second: all samples were sent out to an outside laboratory (there is no in-house laboratory, so all the micro-testing is based on the reports received and we are supposed to believe them and TRUST them). With that being said, the abnormal organoleptic testing result in the 5th day does coincide with my in-house testing. Not sure about the estimation - could be just your answer TNTC.
So, I had to report all these to the higher-ups. Now, I am trying to find solutions that will still get us to a 7 day shelf-life - just good business.