THE INTERFERENCE OF NONIONIC EMULSIFIERS WITH PRESERVATIVES VIII By JOHANNA POPRZAN and MAISON G. DENAVARRE Presented September 18, 1958, International Symposium, Gesellschaft Deutscher Kosmetik Chemiker, Bonn, Germany IN THE COURSE of investigating the inactivation of preservatives by nonionic surfactants, a number of significant developments were noted but hitherto not published. In addition other progress has suggested new lines of research in this unsolved problem. Indeed, the recent report (1) that 3 per cent hexylene glycol was used successfully with 0.2 per cent sorbic acid to preserve a nonionic product has led us to re-examine some earlier results (1955) and to further examine the effect of all commonly used glycols along with other polyols. Propylene glycol had been used as a solvent for preservatives in one of our (M. G. deN.) early experiments. Checking the glycol controls led to the verification of the established inhibitory concentration for propylene glycol against/Ispergillus niger. This was found to be at least 16 per cent, in Jaag medium, with or without the presence of the nonionic G-3720. This figure is somewhat higher than the published concentrations recom- mended. However, when the glycol, 0.1 or 0.2 per cent methyl p-hydroxy- benzoate and 2 per cent G-3720 were added to Jaag medium, there were in- dications that somewhat less than 10 per cent propylene glycol would have either a potentiating effect on the preservative, or that it might interfere with the suspected complexing of the preservative with the nonionic. With this background, one of us (J.P.) set up experiments to evaluate the effect of position and number of hydroxyl groups on a polyol in pre- venting inactivation ofmethylp-hydroxybenzoate by nonionics. Experimental. The microSrganisms used in this series were Proteus vulgaris, Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli and /Ispergillus niger. Nutrient broth was the bacterial medium while Czapek Dox medium was used for the mold. The test Inethods and other procedures were the same as one of us had previously published (2). * Cosmetic Laboratories, Inc., Div. of Beauty Counselors, Inc., Detroit 7, Mich. 81

82 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The commercial nonionic G-3720 was used throughout this work. It is a polyoxyethylene (20) stearyl alcohol. A 2 per cent concentration was used. Tween 80 was used in a concentration of 2 per cent in some tests. It is a polyoxyethylene (20) sorbitan oleate. Methyl p-hydroxybenzoate 0.2 per cent was the only preservative tried. Varying amounts of glycol were used as the test required with due adjustment of water content to compensate for the glycol (1). The polyols used were propylene glycol of commerce 1,3-propanediol dipropylene glycol 1,4-butanediol hexylene glycol sorbitol and glycerol. Discussion. In this work, results with molds cannot be considered on the same basis with usual bacteriological tests. Thus, it is found that Jaag medium preserved with 0.1 per cent methyl p-hydroxybenzoate showed no growth of,4. niser for four months. At the end of seven months, a very heavy growth was obtained. Too often such tests are reported on a seven-, fourteen- or thirty-day basis. Our tests with molds are con- tinued for at least a year. If the number and position of hydroxyl groups on a polyol have an effect on preservative inactivation, then it is desirable to examine the configuration of the polyols used. The propylene glycol of commerce is largely 2,3-propanediol with a small amount, rarely over 5 per cent, of 1,3-propanediol. Hexylene glycol of commerce is 2-methyl 2,4-pentanediol having the following configuration: HO OH I I HaC--C--C--C--CHa H H HCa Hexylene Glycol H H H H--C--C--C--H HO H OH 1,3-Propanediol H H H I I I HC--C--CH H OH OH 2,3-Propanediol In hexylene glycol, the two hydroxyl groups are not attached to adjacent carbons as they are in ordinary propylene glycol. This configuration could account for the difference in behavior. At the same time if this line of reasoning is valid, then such commercial compounds as 1,4-bu- tanediol, 1,3-butanediol, hexanetriol-l,2,6 and others may have similar effects, but sorbitol and glycerol would be comparatively ineffective. Results. We find that 8 per cent propylene glycol when added to the