Optimization of an onion oil microemulsion by response surface methodology for enhanced physicochemical stability and biological activity

Onion oil (OO) containing propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO) is known for various therapeutic properties. However, its industrial use in hydrophilic matrices is challenging due to the lack of physicochemical stability. Applying Box-Behnken design (BBD), we developed an optimal OO microemulsion (OOME) with a minimum droplet size and maximum chemical stability. The OOME comprised 2 % w/w oily phase (high oleic acid sunflower oil), 120 mg/L of OO containing PTS+PTSO, 1.47 % w/w emulsifier (Diacetyl tartaric acid ester of mono-diglycerides, DATEM), 0.25 % stabilizer (xanthan gum) and 573 mM phosphate buffer. Turbidimetry as well as laser and dynamic light scattering over 30 days was used to characterize physical stability of the OOME, assessing chemical stability by HPLC. Cytotoxicity and quantification of cytokines (IL-4 and IL-8) were evaluated in colorectal cancer cells (HT-29, T-84 and SW-837) culture supernatants. After 30 days of storage, OOME remained stable, with no flocculation or coalescence phenomena. It achieved a PTS+PTSO amount of 98 mg/L, a droplet size of 329 nm, a particle size dispersal coefficient of 0.89, and Z-potential was −40.17 mV. The OOME improved the antitumor effect of OO in lines HT-29 and SW-837, as well as its influence on the inflammatory response. [Display omitted] •Onion oil is loaded in microemulsion (OOME) produced by a rotor-stator homogenizer.•Box-Behnken design is used to optimize the processing conditions for a stable OOME.•The physical and chemical stability of OOME was assessed by different techniques.•OOME increased the cytotoxic effect of onion oil (OO) against HT-29 and SW-837.•OOME improved the effect of OO on the levels of cytokines produced by HT-29 cells.