title: Optimization of cosmetic preservation: water activity reduction.
abstract: OBJECTIVE
  Preservation of cosmetics is a prerequisite for industrialization, and among the proposed solutions, self-preserved cosmetics are of great interest. One key influencing parameter in self-preservation is water activity; its reduction can help to fight against microbial growth in cosmetic products. This work presents a study on the influence of humectants on water activity and its consequence on the preservation of cosmetic formulations.
  
  
  METHODS
  First, water-humectants mixtures were considered. The influence of glycol and glycerin content, glycol chemical structure, glycerin purity and formulation process on the water activity of the binary mixture was studied. Molecular modelling was performed for a better understanding of the impact of glycol chemistry. Then, the results were applied to five different cosmetic formulations to get optimized products. Challenge test on five strains was carried out in that sense.
  
  
  RESULTS
  We showed that the higher the humectants concentration, the lower the water activity. Glycol chemical structure also influenced water activity: propan-1,2-diol was more efficient than propan-1,3-diol, certainly because of a better stabilization in water of propan-1,2-diol as shown by DFT calculation. A drop by drop introduction of glycol in water favoured aw reduction. The best water activity loss was 6.6% and was reached on the cream formulation whose preservation was improved as evidenced by challenge test.
  
  
  CONCLUSIONS
  Fabrication process as well as humectants concentration were shown to influence water activity. The hydroxyl group positions as well as the presence of an alkyl group on the glycol carbon chain impacted water binding as suggested by DFT calculation. Reducing aw improved the preservation of a cosmetic cream, inhibiting or slowing down the growth of bacteria and fungi.
authors.affiliation: SO.F.I.A. Cosmétiques, 1ère Avenue, 1ère Rue, 06514, Carros, France; Université de Nice Sophia Antipolis, ICN, UMR 7272, Parc Valrose, 06108, Nice CEDEX 2, France.
authors.forename: A
authors.initials: A
authors.lastname: Kerdudo
authors.forename: F
authors.initials: F
authors.lastname: Fontaine-Vive
authors.forename: A
authors.initials: A
authors.lastname: Dingas
authors.forename: C
authors.initials: C
authors.lastname: Faure
authors.forename: X
authors.initials: X
authors.lastname: Fernandez
mesh_terms: D003358:Cosmetics; D014867:Water
chemical_list: D003358:Cosmetics; D014867:Water
keywords: formulation; glycol; microbiology; polymer; preservation; water activity