Study Maps How Common Preservatives Disable Bacteria

A collaborative study has shed light on the molecular workings of two widely used preservatives, sodium benzoate (SB) and phenoxyethanol (POE), revealing that they disable bacteria through a coordinated, multi-target attack rather than a single mechanism.

The research, carried out by the Institute of Nano Science & Technology and Unilever R&D, Bengaluru, combined transmission electron microscopy with biochemical analyses to examine how the preservatives act on two representative bacterial pathogens: the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa.

Sodium benzoate, in use since the early 1900s, is a common preservative in foods such as pickles, ketchup and fizzy drinks. Phenoxyethanol is found in shampoos, moisturisers, sunscreens and some vaccines. Despite their long-standing use, the precise ways in which they kill bacteria had remained poorly understood.

The study found that the preservatives compromise the physical integrity of the microbial cell envelope while also causing reactive aldehydes and oxygen-derived species to build up inside the cell. These reactive molecules disrupt essential proteins, genetic material and other critical cellular functions.

Imaging showed that the two compounds follow distinct routes to inactivation. Sodium benzoate caused cells to shrink and collapse, whereas phenoxyethanol led to membrane expansion and eventual rupture.

The researchers also found that sodium benzoate becomes markedly more potent in acidic conditions, with an approximately 16-fold increase in activity, while phenoxyethanol maintained consistent efficacy across a broad pH range.

These differences carry practical implications. Knowing how each preservative works can help manufacturers select the right one for a given product format — sodium benzoate for acidic formulations, and phenoxyethanol where pH variation is not a concern. Such insights could allow companies to use appropriate concentrations, reduce spoilage and waste, and stay ahead of bacteria that might otherwise develop resistance.