With natural cosmetics market blooming in recent years, the microbiological quality of cosmetic products has become a significant part of development and innovations in the cosmetic industry. Microbial spoilage leads to product degradation or in case of pathogens to potential health risks. To ensure consumer safety and protect cosmetic products against microbial contamination, we commonly use preservative. Results of research regarding the safety of certain chemical preservatives has driven the cosmetic industry to seek for their alternatives of natural origin. Hence, there is ample interest in development of cosmetic products in which traditional preservatives are replaced with antimicrobial substances of natural origin.
In the master thesis we investigated the efficacy of 33 commercially available antimicrobials of natural origin. We used the minimum and maximum concentrations recommended by the manufacturer. Firstly, we analysed dermal formulations for total aerobic bacterial count and total combined yeast count according to European Pharmacopeia to determine the initial number of microorganisms. The test was repeated 2 months after first opening to establish potential microbial growth. The formulation with 1,0 % Leucidal® Liquid PT (Lactobacillus ferment) did not fulfil the criteria as it showed signs of fungal contamination, whereas all other tested formulations exhibited proper microbiological quality.
Secondly, we performed a challenge test according to ISO 11930 standard, where we inoculated the formulations with Pseudomonas aeruginosa and Aspergillus brasiliensis and then observed the reduction of microorganisms during 28 days. In the challenge test with P. aeruginosa, the criterion was fulfilled by all formulations excluding one without a preservative and 1,0 % Leucidal® Liquid PT. As for A. brasiliensis; the formulations that did not fulfil criterion were 0,2 % Geogard® 221 (Dehydroacetic Acid, Benzyl Alcohol), 1,5 % Verstatil® SL (Aqua, Sodium Levulinate, Potassium Sorbate) and 2,0 % Verstatil® Synacid (Aqua, Glycerin, Sodium Levulinate, Sodium Salicylate, Sodium Anisate). We noticed organoleptic changes and signs of mold growth on the walls of containers in several formulations meeting criterion. Although ISO standard 11930 does not explicitly describe the procedure in this particular situation, we interpreted that preservation efficacy of the following antimicrobials is not sufficient: 2,0 % and 4,0 % Arborcide OC (Aqua, Leuconostoc Ferment Filtrate), 2,0 % Leucidal® Liquid (Leuconostoc/ Radish Root Ferment Filtrate), 2,0 % Leucidal® Liquid Complete (Aqua, Leuconostoc/ Radish Root Ferment Filtrate, Coconut Fruit Extract), 0,25 % Plantservative WSr (Lonicera Japonica Flower Extract, Lonicera Caprifolium Flower Extract), 2,0 % Dermosoft 1388 ECO (Aqua, Glycerin, Sodium Levulinate, Sodium Anisate), 0,05% Dermosoft Anisate ECO (Sodium Anisate), 1,0 % and 3,0 % Phytocide Black Currant Powder (Black Currant Fruit Extract).