Home Cosmetic Science Talk Formulating Advanced Questions Water activity required for growth of Pseudomonas aeruginosa

  • Water activity required for growth of Pseudomonas aeruginosa

    Posted by Abdullah on April 16, 2022 at 1:48 am

    1. How much water activity is required for growth of Pseudomonas aeruginosa in lotion and cleanser? 

    2. What percentage of NACL in cleansing product and glycerin in lotion can lower water activity enough that can prevent growth of Pseudomonas aeruginosa?

    I am using preservatives against both bacteria and fungi(formalin+ CMI MI+ EDTA in cleansers & phenoxyethanol+ caprylhydroxamic acid+ EDTA currently in emulsions) but as it looks like P. aeruginosa is more sensitive to water activity than any other microbe, i thought if it is possible to prevent its growth with NACL or glycerin to be more confident against it.
    I will happily use up to 5% NACL and >10% glycerin in products.

    From my studying i got the idea that this is the most dangerous microb from cosmetics & grows in any type of product and packaging faster than any other microb and the water that we use in cosmetics always have it.

    Abdullah replied 2 years, 1 month ago 3 Members · 11 Replies
  • 11 Replies
  • PhilGeis

    Member
    April 16, 2022 at 10:49 am

    Reliable Aw inhibition of pseudomonads typical of cosmetic contaminants - ~60% glycerol and ~20% NaCl.    Neither reliably kills.
    Most common is Burkholderia cepacia - Pseudomonas aeruginosa is second but prob somewhat greater health risk.    

  • Abdullah

    Member
    April 16, 2022 at 11:21 am

    PhilGeis said:

    Reliable Aw inhibition of pseudomonads typical of cosmetic contaminants - ~60% glycerol and ~20% NaCl.    Neither reliably kills.
    Most common is Burkholderia cepacia - Pseudomonas aeruginosa is second but prob somewhat greater health risk.    

    Thanks 

    I saw in one website that required Aw for Pseudomonas aeruginosa is 0.98 and 15% glycerin or 5% NACL reduces Aw to below 0.98. so i thought these two ingredients at these amounts may be able to prevent the growth of Pseudomonas aeruginosa. Of course i will have preservatives and flip top cap package for all products too.

    Will these two at least help preservation or they are useless at all?

    And is Burkholderia cepacia only manufacturing contaminant or it can be introduced to product by consumer use too? 

  • PhilGeis

    Member
    April 16, 2022 at 11:32 am

    0.98 might be optimal but >.90 and less than .98 is not prohibitive.
    Not aware of Aw data for combinations.

  • Abdullah

    Member
    April 16, 2022 at 11:50 am

    PhilGeis said:

    0.98 might be optimal but >.90 and less than .98 is not prohibitive.
    Not aware of Aw data for combinations.

    It is also not combination. NACL was for cleansing product and glycerin for emulsion. 

    Thanks for clarification.

  • Microformulation

    Member
    April 16, 2022 at 7:05 pm

    How will you be measuring Aw?

  • Abdullah

    Member
    April 17, 2022 at 1:20 am

    How will you be measuring Aw?

    I will not measure it myself. I will use the data from those who has already measured it. 
    Like this one for example. 

  • PhilGeis

    Member
    April 17, 2022 at 11:19 am

    Different folks publish different numbers - and remember, you have a product not a simple solution.

  • Abdullah

    Member
    April 17, 2022 at 1:50 pm

    PhilGeis said:

    Different folks publish different numbers - and remember, you have a product not a simple solution.

    Will it be different if it is in the product or only water?

    If yes then it should be better in product because there is surfactants and oil phase and other ingredients in product too so glycerin or NACL to water ratio is higher than only glycerin or NACL in water. Isn’t it so? 

  • PhilGeis

    Member
    April 17, 2022 at 1:56 pm

    One cant presume one way or the other.  We rarely have simple solutions.

  • Microformulation

    Member
    April 17, 2022 at 2:50 pm
    Aw can NOT be calculated accurately. It must be measured.
    “However, it is practically impossible to calculate water activity,
    therefore it is far better to measure it by instrumentation. The foods
    industry has used water activity for many years to determine the need
    for
    preservatives.

    There
    are several ways to measure water activity including vapor pressure
    manometry, electric hygrometry, hair hygrometry, and dew point. The
    Association of Official Analytical Chemists (AOAC) has officially
    recognized the dew-point/chilled mirror method.”

    https://www.cosmeticsandtoiletries.com/cosmetic-ingredients/preservation/article/21834662/effective-vs-ineffective-preservation-using-water-activity

    That is an article from David Steinberg, a well-known Cosmetic author, and renowned expert.

    Aw (water activity) is vastly different than the percentage of water in the Formula (a common mistake). It is affected by numerous other factors.

  • Abdullah

    Member
    April 17, 2022 at 3:03 pm

    Thank a lot

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