Characterization of hemp seed oil emulsion stabilized by soap nuts (Sapindus mukorossi) extract

In the past years, plant-based surfactants such as plant proteins, hydrocolloids, and extracts have intrigued scientific studies of food formulations for usage in emulsion, nanoemulsion as well as microemulsion systems, mainly due to their functional benefits and low toxicity levels. In this work, a hemp seed oil-containing (HSO) emulsion system was stabilized using soap nuts (SN), also known as Sapindus mukorossi. In order to determine the formulation requirements and the optimal emulsion composition including oil and surfactant content, a Box-Behnken experimental design was applied. The compositions were evaluated in terms of their particle size distribution, stability, visual quality, turbidity, and zeta potential. Moreover, to describe the physicochemical characteristics of the emulsions, rheological tests, Fourier transform infrared spectroscopy (FTIR) analyses, and refractive index parameters were also studied. The average particle size of the emulsions (particle distribution by number) was recorded between 51 and 103 nm, and z-ave parameter reached values between 227 nm and 311 nm. The zeta potential increased when the proportion of HSO increased, and reached its highest value (−23.5 mV) when HSO was 5% v/v. Microscopic investigations confirmed the polydispersity of the prepared emulsions. Furthermore, due to further applications of the emulsions i.e. packing and delivery, wetting properties were evaluated. The wetting angle values reached maximum approx. 30° with an HSO content of 1%. However, the wetting angle values were lower with increasing HSO content. Presented results revealed that Sapindus mukorossi is indeed a good stabilizer for hemp seed oil and water emulsions.