The motivation behind the work stems from a growing environmental reckoning with conventional surfactants. These workhorse molecules, which make up 10 to 20 percent of most cosmetic emulsions, are designed to reduce tension at the boundary between water and oil, allowing otherwise incompatible phases to blend into smooth, shelf-stable products. Yet many synthetic surfactants persist in the environment for years. Perfluorinated compounds in particular are prized by formulators for their robustness but are notoriously resistant to degradation, while linear alkylbenzene sulfonates have been linked to biochemical and pathological harm in aquatic ecosystems. Regulators and consumers alike have been pushing the cosmetics industry to find biodegradable alternatives that do not sacrifice performance.

Biosurfactants, amphiphilic molecules produced by microorganisms that combine a water-loving polar head with an oil-loving hydrophobic tail, have long been touted as such an alternative. Lactic acid bacteria are especially attractive producers because they carry the Generally Recognized as Safe designation, meaning their metabolites face fewer regulatory hurdles in food and personal-care applications. The obstacle has been practical: production yields are often low and fermentation substrates expensive, pushing up costs and limiting commercial adoption. Researchers have therefore been hunting for high-performing producer strains in unconventional places, from cassava-processing effluents to traditional fermented foods.

Pendidam, the spontaneously fermented skimmed cow’s milk consumed around Ngaoundere in Cameroon’s Adamaoua region, had already caught the attention of the research group. Earlier work by Mbawala and colleagues had shown that the drink teems with Lactobacillus strains capable of producing surface-active compounds. In the new study, the team collected six Pendidam samples from vendors at four sites across the city, including the Petit marché, Dang, Wakwa and the Grand marché, and transported them to the laboratory under refrigeration within two hours of purchase.

From those samples the researchers isolated twelve presumptive Lactobacillus strains, all of which proved to be Gram-positive, non-motile, catalase- and oxidase-negative rods with heterofermentative metabolism, growing across a temperature range of 15 to 45 degrees Celsius and tolerating salt concentrations up to 6.5 percent. The authors are careful to note that these phenotypic traits, while consistent with members of the former Lactobacillus group and suggestive of the reclassified genus Lactiplantibacillus, are not sufficiently discriminating for definitive taxonomic assignment following the genus’s recent fragmentation into more than twenty genera; molecular identification by 16S rRNA gene sequencing remains a stated priority for future work.

Screening for biosurfactant production relied on two complementary assays. In the hydrocarbon overlay test, bacterial colonies grown on agar were covered with palm oil; the appearance of clear halos containing microemulsions signaled secretion of surface-active compounds. The oil spreading test provided quantitative confirmation: drops of cell-free culture supernatant were deposited onto a thin oil layer floating on water, and the diameter of the resulting clear zone, which correlates with biosurfactant concentration, was measured. Five isolates, subsequently designated S1 through S5, produced clear zones ranging from 6 to 28 millimeters, comfortably exceeding the 3-millimeter threshold above the negative control that the field considers evidence of genuine biosurfactant production.

The crude biosurfactants were then extracted by ethanol precipitation from scaled-up cultures and put through their paces. Emulsification indices, a measure of the emulsified layer formed when biosurfactant solution is mixed with palm oil, ranged from 67.33 to 72 percent, values slightly below those reported for some purified lactobacilli biosurfactants in the literature but respectable for unpurified crude extracts. More striking were the surface tension measurements. At a concentration of 4 grams per 100 milliliters, solutions of the biosurfactants from isolates S1 and S5 lowered the surface tension of water from 70.90 millinewtons per meter to levels comparable with sodium dodecyl sulfate, the benchmark anionic surfactant used as the positive control.

The decisive test came when the biosurfactants were formulated into water-in-oil beauty milks alongside xanthan gum, sesame oil, glycerol and shea butter, with the commercial sorbitan monostearate SPAN 60 and a marketed body milk serving as positive controls. Laser diffraction analysis using a Malvern Mastersizer 2000 revealed that emulsions stabilized with the bacterial surfactants formed droplets between 4.94 and 7.61 micrometers in diameter, dramatically finer than the 16.34-micrometer droplets of the negative control. The standout was isolate S5, whose biosurfactant yielded the smallest droplets of all, significantly finer even than those produced by the synthetic SPAN 60. According to the authors, this reflects rapid adsorption of the amphiphilic molecules at newly created oil-water interfaces during high-shear homogenization, where they form protective films that generate steric and, depending on molecular composition, electrostatic repulsion between droplets, suppressing coalescence and Ostwald ripening.

Viscosity told a complementary story. Formulations containing the bacterial biosurfactants ranged from 967 to 1715 millipascal-seconds, compared with roughly 1998 millipascal-seconds for both controls, and the differences tracked closely with droplet size. Emulsions with the finest droplets, such as those made with the S5 biosurfactant, maintained relatively high viscosity, consistent with emulsion theory: smaller droplets present a larger total interfacial area, increasing interactions between dispersed and continuous phases and raising resistance to flow. Higher viscosity in turn slows droplet mobility, reducing collision frequency and the risk of creaming or phase separation during storage. The combination of fine droplet size and appropriate rheology, the authors argue, positions the S5 biosurfactant as the most promising candidate of the five tested for cosmetic formulation.

The study’s novelty lies less in the individual measurements than in its integrated approach and its source material. Biosurfactants from lactic acid bacteria have mostly been studied for antimicrobial, antiadhesive and probiotic properties; direct deployment as emulsifiers in cosmetic products has rarely been evaluated, and never before with strains from Pendidam. By connecting microbiological screening with rigorous physicochemical characterization of finished emulsions, the work makes the case that traditional fermented foods are an underexplored reservoir of industrially useful microbes, and one that comes with built-in cultural and economic advantages for the communities that produce them. The path to commercialization still requires purification and structural characterization of the biosurfactants, definitive molecular identification of the producing strains, long-term stability testing and safety evaluation, but the baseline data now exist. For an industry under pressure to replace persistent synthetic surfactants with biodegradable molecules, the answer may have been fermenting quietly in a Cameroonian milk calabash all along.

Subject of Research: Biosurfactants from Lactobacilli isolated from Pendidam fermented milk for stabilizing water-in-oil cosmetic emulsions

Article Title: Improvement of water in oil emulsion physicochemical stability using biosurfactants from indigenous Lactobacilli isolated from Pendidam

Article References: Improvement of water in oil emulsion physicochemical stability using biosurfactants from indigenous Lactobacilli isolated from Pendidam. (n.d.). https://doi.org/10.1007/s44508-026-00021-y

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00021-y

Keywords: biosurfactants, Lactobacilli, Pendidam, emulsifiers, cosmetics, lactic acid bacteria, water-in-oil emulsion, droplet size, viscosity, surface tension, fermented milk, sustainable ingredients