Preservation – self-preserving antimicrobial action

Published: 3-Oct-2011

Ingredients supplier Campo tests the antimicrobial efficacy of Lonicera caprifoleum and Lonicera japonica (honeysuckle) extracts when combined with antimicrobials glyceryl caprylate, p-anisic acid, levulinic acid and ethanol in a series of \'preservative-free\' formulations

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Developing new cosmetic formulations by replacing chemical preservatives with ingredients with antimicrobial properties not legislated as preservatives is a key route to developing preservative-free or self-preserving cosmetics. S Papageorgiou, A Varvaresou, E Tsirivas and C Demetzos introduce work on a series of combination ingredients

Microbial spoilage of cosmetic formulations has always been of special concern for the industry since it can lead to product degradation. Chemical preservatives are added to cosmetics to protect them against microbial contamination.

A recent trend is the replacement of traditional chemical preservatives by antimicrobial agents that are not legislated as preservatives according to Annex VI of Commission Directive 1976/768/EEC (3-5) but that are safe and effective as preservatives.

An approach to achieve preservative-free cosmetics is the selection of natural compounds that have been characterised as safe and effective against microorganisms, in order to decrease or to eliminate the use of the traditional chemical preservatives.

A number of plant derived essential oils and extracts exhibit excellent antimicrobial properties and have been used for the effective preservation of cosmetic formulations. Among others, derivatives of Rosmarinus officinalis, Lavandula officinalis, Thymus vulgaris and Eucalyptus globulus are effective natural preservatives.

Medium polar substances are also alternative antimicrobial agents. Caprylyl glycol and monoglycerides of capric acid and caprylic acid, besides being moisturising agents, exert antimicrobial activities. Due to their emulsifier-like structure they interfere with the cellular structures of microorganisms and disintegrate cell membranes.

We have to keep in mind that the chemical composition of fragrances plays a key role concerning the antimicrobial activity of essential oils and extracts obtained from natural sources. Various aldehydes and alcohols are among the most active compounds. In the past, a fragrance mixture consisting of benzyl acetate, phenethyl alcohol and linalool had been proposed as an alternative preservative. Today several antimicrobial fragrance ingredients are commercially available, such as p-anisic acid (p-methoxy-benzoic acid) and levulinic acid (4-oxo-pentanoic acid), which were found to be the main compounds in Pimpinella anisum and other herbs and in Dioscorea villosa as a by-product in the production of diosgenin from wild yam respectively.

Based on the above comments concerning the development of self-preserving cosmetics, Campo focused its research on the evaluation of the preservative efficacy of the antimicrobial extracts of Lonicera caprifoleum and Lonicera japonica (table 1) in combination with other antimicrobials such as glyceryl caprylate, p-anisic acid, levulinic acid (table 2) and ethanol in a series of aqueous and o/w emulsions.

Lonicera extracts are described as being a mixture of esters of lonicerin and p-hydroxy benzoic acid, the structures of which are very similar to those of parabens. Although Lonicera caprifoleum and Lonicera japonica extracts are well known for their antimicrobial properties, there are no studies in the literature regarding their incorporation as preservatives in cosmetic formulations. In order to evaluate the preservative efficacy of these multifunctional ingredients, challenge tests (preservative efficacy tests, PETs) were performed according to the standards proposed by the European Pharmacopoeia.

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