Spontaneous nanoemulsion of black cumin seed (Nigella sativa) extract: Effects on physical and chemical properties

Abstract

This research aims to optimize the composition of black cumin (Nigella sativa) seed oil nanoemulsion based on the spontaneous emulsification technique. Two factors were studied: (1) oil-surfactant ratios (1:1, 1:2, 1:3) and (2) the type of surfactants (Tween 60, Tween 80). Physical properties measured included particle size, polydispersity index (PDI), zeta potential, conductivity, absorbance, transmittance, pH, and viscosity, while chemical properties measured included antioxidant activity and total phenolic content. The results showed particle sizes of the nanoemulsion ranging between 29.77 nm (for 1:3, Tween 60) and 442.63 nm (for 1:2, Tween 80). ANOVA revealed that oil-surfactant ratio and the type of surfactants significantly impacted droplet size and PDI. Smaller and more uniform droplets (PDI 0.3-0.5) were obtained with Tween 60, while Tween 80 resulted in larger, more heterogeneous droplets (PDI 0.4-0.7). Zeta potential values (-1.91 to -17.94 mV) were all below the threshold value provided in the literature, indicating inadequate electrostatic stabilization. Conductivity values (0.0427-0.1033 ms/cm) followed the expected range. Higher oil-surfactant ratios for nanoemulsions made with Tween 60 reduced absorbance and increased transmittance, indicating enhanced optical clarity. Antioxidant activity was highest (5.70%) in nanoemulsions with a 1:1 oil-surfactant ratio using Tween 60, compared to the lowest (3.30%) in nanoemulsions with a 1:3 ratio using Tween 80. Total phenolic content varied (0.193-0.852 mg GAE/g) significantly (p < 0.05) as influenced by composition. Generally, Tween 60 resulted in better black cumin seed nanoemulsions with improved physical and chemical characteristics.