Preservative effectiveness testing
Preservative effectiveness testing was described through
the method reported by Campana et al.
8,12
The
antimicrobial preservative efficacy of cosmetic products
was investigated using P. aeruginosa ATCC 9027 as
recommended by USP XXVI for the evaluation of
antimicrobial protection of cosmetic products. The test
organism was grown on TSA and harvested with sterile
phosphate buffer, pH 7. The absorbance of the test
organism suspension containing 1 x 10
8
cfu/ml was
determined using spectrophotometer at 625 nm
wavelength. Fifty grams of each product sample was
weighed aseptically into respective sterilized conical
flask and each inoculated with 0.1 ml of test inoculum
suspension. The respective samples were properly mixed
until a homogeneous suspension was obtained and
incubated at 28°C for 28 days. Thus each initial test
product contained approximately 2.0 x 10
5
cfu/g as at the
time of experiment. Two gram of respective samples was
aseptically drawn at 0, 7, 14, 21, and 28
th
day into
separate neutralizing medium and subsequently plated for
viable count as described above. Un-inoculated sample of
each product was used as control. The product was
considered as adequately preserved when 99.9%
reduction of the initial inoculum count was obtained on
the 7th day of incubation and remained with no i ncrease
as the incubation period progressed until the final day of
the experiment.