The solubilisation and inactivation of preservatives by non-ionic detergents

Survey of micro-organisms associated with spoilage of cosmetic creams manufactured in South Africa

Synopsis Two studies were conducted to determine the predominant micro-organisms found in spoiled cosmetic creams manufactured in South Africa. The products evaluated included facial creams and hand and body lotions. Spoiled cosmetic creams were obtained from different manufacturers and analysed microbiologically for the presence of bacteria, yeasts and moulds. The frequency and relative density (percentage) of micro-organisms isolated from naturally spoiled creams were calculated. Pseudomonas aeruginosa and Enterobacter gergoviae were the most predominant bacteria, whilst Candida parapsilosis and Aspergillus flavus were the most predominant yeast and mould, respectively. Of all the samples examined, approximately two-thirds (69%) were due to microbial spoilage. This study highlighted the importance of adopting suitable quality control guidelines for the local cosmetics industry, similar to those currently used by international cosmetics manufacturers.

Oxidation of benzaldehyde in some single phase betaine-benzaldehyde-water systems

The oxidation rates of increasing concentrations of benzaldehyde in ternary systems of the L1 type have been measured in aqueous solutions of four betaine homologues. On applying corrections for extra-micellar material, the rate becomes independent of the betaine concentration and is related to the micellar ratio of benzaldehyde to betaine when this ratio exceeds 1. The rate of oxidation in an LC system has been determined and compared with that in L1 systems. The site and mechanism of the oxidation reaction in these systems is postulated.

Effect of inorganic additives on solutions of nonionic surfactants VI: Further cloud point relations

Disperse dosage forms stabilized with nonionic surfactants frequently contain electrolytes as active ingredients or adjuvants. Salting out of the surfactants by these electrolytes may cause breakdown of the dosage forms. The cloud point of an aqueous solution of octoxynol 9 was used to measure the salt effects. Electrolytes which salt octoxynol 9 out lower its cloud point, while salting-in electrolytes raise it. The observed cloud point effects are discussed according to the mechanisms involved. Salting out by dehydration in competition with octoxynol 9 for the available water was observed with sulfate and phosphate anions, sodium, potassium, and ammonium tribasications, and the nonelectrolyte sorbitol. The extensive self-association of water by hydrogen bonds at and below room temperature weakens its solvent power. Ions which reduce this self-association, breaking the structure of water, increased the cloud point of octoxynol 9. Among them were the iodide, thiocyanate, and nitroprusside anions. Ions which tighten the structure of water and enhance its self-association salted the surfactant out, lowering its cloud point. Among these were the fluoride and hydroxide anions. Complex formation between the ether linkages of octoxynol 9 and the following cations increased its cloud point: hydrogen (from strong acids), silver, magnesium, and zinc. Including published data, the only cations which do not form complexes with polyoxyethylated surfactants (and are, therefore, unable to salt them in) were the alkali metal ions sodium, potassium, and cesium and the ammonium ion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of polyols on interaction of paraben preservatives with polysorbate 80

A quantitative study of the interaction of the methyl, ethyl, propyl, and butyl esters of p-hydroxybenzoic acid with polysorbate 80 in the presence and absence of two polyols (propylene glycol and glycerol), which were potential competitors, was performed. The results indicate that neither competitor displaced significant amounts of the parabens from their binding sites on polysorbate 80. The previously observed synergistic antimicrobial effects of these polyols appear to be due to a mechanism other than the displacement of the parabens from their micellar binding sites.

Competitive interaction of preservative mixtures with cetomacrogol

The binding of various preservatives, alone and in pairs, to cetomacrogol has been investigated. Data for the compounds alone indicate that all preservatives combined with two distinct classes of sites in the cetomacrogol micelle. The data were expressed in the form of Scatchard plots and the association constant and number of sites in each class were calculated. All combinations of preservatives were shown to exhibit substantial competition resulting in diminished binding, however the nature of the competitive process is not the same in all cases. Chloroxylenol and dichloroxylenol do not compete significantly with methyl paraben in the first class of sites, but substantial competition was observed in the second class. In contrast, methyl paraben and propyl paraben compete strongly for the first class of sites. Competition with these compounds also occurred in the second class of sites but this was coincident with a large increase in the number of secondary binding sites which tended to increase binding.

Interaction of preservatives with cetomacrogol

The interaction of a number of commonly used preservatives (benzoic acid, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, propyl p-hydroxybenzoate and chloroxylenol with the non-ionic surfactant cetomacrogol was examined and a comparison made of various methods of expressing this interaction. It is suggested that the Scatchard equation is the most satisfactory equation for describing the binding data. Binding parameters determined from a Scatchard plot in the concentration range of free preservative appropriate for antimicrobial activity can be used to calculate the total concentration of preservative required in the surfactant system.

A model for the influence of emulsion formulation on the activity of phenolic preservatives

Basic mathematical models are suggested for calculating the concentration of preservatives which is chemically available in the water of emulsions. It is influenced by the total concentration of preservative in the emulsion, the oil: water partition coefficient of the preservative, the oil: water ratio and the concentration of emulgent. The activity of the preservative is related to the concentration free in the water.

The effects of polyoxyethylene compounds on the hydrolysis of chlorbutol

The rates of hydrolysis of chlorbutol are reduced by surface-active agents, but not by polyethylene glycols. The ratio of the rate-constant in simple aqueous systems to that in systems containing surface-active agents can be predicted if the distribution coefficient for chlorbutol between the micellar pseudo-phase and the aqueous phase is known and is independent of concentration.

Effect of solubilisation on the antibacterial activity of hexachlorophane

The solubilisation of hexachlorophane by various non-ionic agents has been studied at pH 2·5 and 8·0. The interaction of the phenol with these agents in unsaturated systems at pH 8·0 has been determined by a dialysis technique using rubber latex membranes. The bactericidal activity is shown to depend on the concentration of unbound hexachlorophane, but this is not simply related to the degree of saturation of the total system. The results of agar-plate diffusion tests cannot be correlated with either the concentration of unbound hexachlorophane or the total concentration.