6 replies to this topic

[Keppie5555]

Good evening,

Our oil bath is broken and we have to heat treat our samples (skim milk powder) at 106 c. Is it plausible to do the heat treatment in an autoclave set a 106 degs. Will the pressure of the autocalve will give an erroneous results for our thermophilic count? Thanks in advance.

[Scampi]

Perhaps this will help, the pressure plus 120C will actually destroy all of the thermophilic spores, so yes it will give you a false negative

 

www.allinterview.com/showanswers/145970/maintaining-autoclave-temperature-at-121degree-centigrade-pressure-15lbs-not-abo.html

[Keppie5555]

Hi Scampi

i ve set our autoclave for 106 degs and i included our data logger inside to monitor the temp and cycle. The autoclave didnt reach 121 deg and according to our data logger the temp was maintin at 106 degs. Do you think that my heat treatment is accurate for performing the thermophilic spore count even though there was pressure during the holding time of the samples inside the autoclave? Thanks in advance.

[Charles.C]

Good evening,

Our oil bath is broken and we have to heat treat our samples (skim milk powder) at 106 c. Is it plausible to do the heat treatment in an autoclave set a 106 degs. Will the pressure of the autocalve will give an erroneous results for our thermophilic count? Thanks in advance.

 

Hi Keppie,

 

I guess it (initially) depends on the specific capabilities of yr autoclave. Usual ones are oriented to achieve 121degC. Sounds like you are requiring your unit to operate similar to those used for "low temperature steam sterilisation", eg -

 Low temperature Steam Sterilization Cycles.pdf   322.93KB   14 downloads

 

I have no direct experience this spore measurement  but as I understand the procedures for evaluating thermophilic spore formers have proven difficult to standardise so that an "unorthodox"  procedure as you consider may result in yr data being non-comparable to other reference sources.  This problem is discussed in some detail here -

 mesophilic and thermophilic spore counts (2016).pdf   1.03MB   20 downloads

 

PS - you may be (eventually) obliged to validate the temperature profile in yr autoclave, eg analogous to  -

 validation procedure for moist heat sterilization,.pdf   229.88KB   11 downloads

 

PPS - Offhand, i would suspect (much) easier to repair/replace yr oil bath.

[Scampi]

I would agree with Charles. Unless you are prepared to sample and analyze before and after autoclave, I wouldn't risk it. The pressure of the autoclave is the issue, because this is NOT your normal procedure (and I'm guessing you don't have a written deviation) you are really risking the 5 log reduction requirement.  106C is not hot enough to destroy all the spores....

[Ryan M.]

No, the pressure in the autoclave at 106^oC is different than the 106^oC oil bath with no pressure.  You will still have some false negatives.

[thatparksgal]

My lab tests for aerobic thermophilic spores. We put 15mL of the sample into a test tube, cap it, and put them in boiling water (104C). We include a  control tube with a thermometer to monitor the temperature. We put the sample test tube under the height of the hot water and hold it in the water for 10 minutes after the control tube reaches 100C. We then cool the tube immediately in ice water. We then plate the sample.

 

If you don't have a water bath, it may be possible to do the test using a hot plate with boiling water.

 

Hope that helps.