Long-term stability investigation of o/w cosmetic creams stabilized by mixed emulsifier
Authors: Vasiljevic Dragana , Djekic Ljiljana , Primorac Marija 
Published: December 2012

Polyglyceryl-3 Methylglucose Distearate (PMD, TEGO? Care 450, Evonik, Germany)is natural (vegetable), non-ionic, PEG-free emulsifier, suitable for the formulation of oil-in-water (o/w) cosmetic creams and lotions. The oil phase components can be selected from mineral oils, vegetable oils and synthetic esters, which enable different variety of application profile of these emulsions. It is possible to prepare stable emulsions using low-level concentration of the PMD (2-3%) if lotions contain 10-25%, and creams 20-40 % of oil phase. PMD forms liquid crystal structure in the presence of stearic acid, glyceryl stearate, fatty alcohols, or their combinations. The o/w type creams, stabilized by these mixed emulsifiers are complex, multiphase systems. The aim of this work was to formulate, prepare and investigate long-term stability of the o/w creams stabilized by mixed emulsifier polyglyceryl-3 methylglucose distearate/glyceryl stearate/stearyl alcohol, depending on concentration levels of PMD (2% or 3%) and oil:water phase ratio (20:80 and 30:70). The samples were prepared using hot/hot procedure. Organoleptic inspection, centrifugation test, rheological measurements, electric conductivity and pH value measurements were performed 72 h, 1, 3, 12 and 30 months after preparation. The prepared samples were apparently white and homogenous creams. The consistency and homogeneity were preserved after centrifugation of the creams after 72 h, 1, 3, 12 and 30 months storage, and no phase separation could be detected. The pH values obtained are suitable for skin application. Conductivity values (25.2-63.7 ?S cm1, 72 h after preparation) were attributed to the multiple phase o/w emulsions with high percentages of fixed water. Results of the rheological measurements have shown that the investigated creams exhibited non-Newtonian thyxotropic behavior. The concentration of emulsifier PMD and oil phase content had an influence on the rheological parameters of investigated samples. The creams prepared with higher content of emulsifiers (3%) and oil phase (30%) exhibited higher values of apparent viscosities and thyxotropic area. The observed decrease of electrical conductivity and increase of apparent viscosities values, which occurred in the creams during 3 months of storage, were probably attributed to bulk water content decreasing. These changes are mildly expressed in the samples with higher content of oil phase. The obtained results of organoleptic characteristics, pH, electric conductivity value and rheological parameters during 30 months of storage indicate good long-term stability of the o/w creams prepared with mixed emulsifier containing PMD at low concentration levels (2% or 3%). Changes during ageing, caused by structuration of creams were less expressed in samples with 30% of oil phase, however, the observed differences were not related with the PMD concentration. In this case, advantage could be given to o/w cream prepared with 30% of oil phase, stabilized by using 2% emulsifier polyglyceryl-3 methylglucose distearate.