Abstract
Many natural extracts used as cosmetic ingredients are available as solutions prepared in high-boiling-point solvents, called carrier solvents, such as propylene glycol (1,2-propanediol), propanediol (1,3-propanediol) and glycerin. The upstream chemical profiling of these extracts represents a major asset for the cosmetic industry, because it accelerates product development. A new workflow for the rapid characterization of the main metabolites present in natural extracts diluted in propylene glycol and 1,3-propanediol is presented here as an extension of previous works on glycerin-containing extracts. This method is an optimized version of a well-established dereplication procedure and consists of a fractionation by centrifugal partition chromatography followed by 13C nuclear magnetic resonance analysis and dedicated data processing. The concentration by evaporation under reduced pressure was considered as a pertinent preliminary step, particularly adapted to the analysis of highly diluted extracts. A dried hydro-ethanolic extract of Leontopodium alpinum Cass. was prepared at laboratory scale and used for method validation. Three solutions at 5% wt. of dry extract were prepared with propylene glycol/water (1:1), 1,3-propanediol/water (1:1) and glycerin/water (1:1) as carrier solvents. The dereplication workflow was applied to the three resulting L. alpinum extracts. Each study led to the quick identification of 26 metabolites including five flavonoids (luteolin and its derivatives), five hydroxycinnamic acids (among which are leontopodic acids), sugars and organic acids.
Highlights
According to the Coptis ingredients database [4], which references more than 15,000 cosmetic ingredients, approximately one out of two commercial natural extracts is diluted in glycerin or in a glycol
The aim of this research work was to develop an original and efficient workflow for the rapid analysis of the major compounds in natural extracts diluted in propylene glycol or propanediol, two carrier solvents largely present in marketed cosmetic ingredients
The effect of the addition of propanediol or propylene glycol compared to glycerin can be highlighted by means of the size of the biphasic zone of pseudo ternary phase diagrams “glycerin or propanediol or propylene glycol/upper organic phase of (EtOAc/CH3 CN/water 3:3:4)/lower aqueous phase of (EtOAc/CH3 CN/water 3:3:4)”
Summary
An increasing number of natural extracts are proposed to the market as solutions in high-boiling-point solvents, often called carrier solvents, such as glycerin or glycols. According to the Coptis ingredients database [4], which references more than 15,000 cosmetic ingredients, approximately one out of two commercial natural extracts is diluted in glycerin or in a glycol. The most represented glycols are 1,2- and 1,3-propanediol, known in International Nomenclature of Cosmetic Ingredients (INCI) as propylene glycol and propanediol, respectively. These glycols are increasingly added to formulations or used directly as extraction solvents especially in the case of natural extracts, as a texturizing agent or humectant and for stabilization and preservation purposes. In 2019, Herman cited the propylene glycol in his study on antimicrobial ingredients as an alternative to cosmetic preservatives [6]
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