Effect of black seed oil, honey, whey protein concentrate and their interaction on antioxidant activity, elastic modulus and creaming index of O/W emulsions

An emulsion based on a combination of highly-valued black seed oil (BSO) and honey shall be introduced as an emerging nutraceutical since the emulsion could be an efficient carrier for bioactive compounds from both. This study aimed to determine effect of BSO, honey, whey protein concentrate (WPC) and their interaction on antioxidant activity (i.e. IC50, the concentration of sample required to scavenge 50% of 2,2-diphenyl-1-picrylhydrazyl free radicals), elastic modulus (G′) and creaming index (CI) of O/W emulsions by means of a response surface methodology. Twenty emulsions were ultrasonically prepared by using various combinations of BSO (10–20%), honey (10–20% and WPC (2–6%) based on a central composite design. Regression analysis (R2 = 0.92–1.00) revealed that a decrease in the IC50 was mainly due to significant (p < 0.05) linear effect of honey and WPC. The quadratic effect of WPC significantly increased the G′ yet decreased the CI. Synergistic effects of BSO-honey on IC50 and G′ were also significant (p < 0.05). However, the antagonistic effect (p < 0.05) of honey-WPC seemed to increase the IC50. By using the fitted quadratic models, the optimized levels of BSO (20.0%), honey (18.2%) and WPC (6.0%) were proposed and predicted to provide the desired emulsion with IC50 = 0.12 mg/ml, G′ = 606.65 Pa and CI = 1.45%. These values were successfully validated with their respective experimental values.