Antimicrobial effect of 4-hydroxybenzoic acid ester with glycerol

Parabens have been commonly used as preservatives in pharmaceutical and cosmetics industries for almost 50 years. These compounds are thermostable, pH-stable and inexpensive and have a wide antimicrobial effect. The antimicrobial activity of parabens in emulsion system is limited by their poor solubility in water phase, which is increasing with the length of their alkyl chain. The aim of this work was preparation of 1-O-(4-hydroxybenzoyl)-glycerol, more hydrophilic and naturally occurring analogue of parabens, and comparison of its antimicrobial activity with commercially used parabens (4-hydroxybenzoic acid, methylparaben, ethylparaben, propylparaben).

1-O-(4-Hydroxybenzoyl)-glycerol was obtained by the transesterification reaction of methyl paraben with glycerol. Purity was confirmed by determination of melting point and by GC/MSD. Antimicrobial activity of 1-O-(4-hydroxybenzoyl)-glycerol and commercially used parabens was determined by spectrophotometrical monitoring of microbial growth in media containing the testing substances, using spectrophotometers PowerWave XS and Cary 50 Conc.

1-O-(4-Hydroxybenzoyl)-glycerol was prepared with purity >99%. This compound showed antimicrobial activity against all tested microorganisms (Staphylococcus aureus, Escherichia coli, Saccharomyces cerevisiae and Fusarium culmorum). In comparison with other tested substances, 1-O-(4-hydroxybenzoyl)-glycerol showed less inhibitory activity at the highest concentration of 20 mmol/L, with the maximum inhibitory activity ca. 70%. On the other hand, antimicrobial activity of 1-O-(4-hydroxybenzoyl)-glycerol at the lower concentrations (2·5 mmol/L, 1·25 mmol/L) was the same or, in some cases, even higher (S. aureus) in comparison with commercially used parabens.

A novel hydrophilic analogue of parabens was synthetized and tested for its antimicrobial activity against selected microorganisms in model system. This study confirms antimicrobial potential of 1-O-(4-hydroxybenzoyl)-glycerol, which is comparable with other commercially used parabens. Unlike commercial parabens, it is possible to expect more significant antimicrobial activity of 1-O-(4-hydroxybenzoyl)-glycerol in real emulsion systems due to the increased solubility of this substance in water phase and also the lower skin irritation.