Researchers at Institute of Nano Science & Technology (INST) Mohali, an autonomous institute of the Department of Science and Technology, in collaboration with Unilever R&D Bangalore, have made a breakthrough in understanding how preservatives attack and kill bacteria. The study, published in Letters in Applied Microbiology, provides the first visual evidence of preservatives compromising bacterial cells through advanced imaging and chemical analysis.
The research focused on two widely used preservatives: Sodium benzoate (SB), the first food preservative approved by the US FDA in 1908 and used in pickles, ketchup, and fizzy drinks, and Phenoxyethanol (POE), used for decades in shampoo, moisturizer, sunscreen, and certain vaccines. The team investigated these preservatives' effects on two bacterial pathogens: Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa.
The study revealed a dual mode of action where preservatives physically compromise the bacterial cell envelope while simultaneously triggering internal biochemical damage through reactive aldehydes and oxygen-derived species that disrupt essential proteins, genetic material, and critical cellular functions. Advanced imaging showed distinct pathways: sodium benzoate induced cellular shrinkage and collapse, while phenoxyethanol caused membrane expansion and eventual rupture.
A key finding was the pH-dependent efficacy difference: sodium benzoate becomes approximately sixteen-fold more potent in acidic environments, while phenoxyethanol displayed consistent efficacy across a wide pH range. This provides crucial insights for optimizing preservative performance in different formulation conditions.
The research methodology included inhibition zone and MIC assays to determine preservative effectiveness, electron microscopy to observe cell structural changes, dye leakage tests to detect membrane damage, and biochemical assays (MBTH and DCFDA) to measure internal chemical disruption. These comprehensive tests were conducted across both bacterial types and in both neutral and acidic conditions.
The practical implications enable industry to select the optimal preservative for specific product formats—sodium benzoate for acidic products and phenoxyethanol for products with pH variations. This knowledge allows for precise dosing instead of estimation, potentially reducing spoilage and waste while staying ahead of evolving bacterial resistance.