Experimental design and evaluation of the influence of a glucomannan-based thickener on the characteristics of an oil/water emulsion

Abstract

The thickening agents are an important part of the cosmetic formulation, offering an opportunity not only to regulate the product viscosity, but also to improve its stability. But, the way to use them and the impact of these natural ingredients on the qualities of the finished product are not always assessed. In this work, a new multifunctional glucomannan-based blend has been evaluated, the aim was to study its influence on the qualities of an oil/water emulsion. To get a rational understanding of this factor, an experimental design approach was adopted. An Optimal design optimized for a second-degree model (Quadratic) with only 12 runs and 1 repeated point was implemented. From the formulation, three ingredients concentrations varied as following; the thickener, a glucomannan-based blend, from 0.6% to 1.2%, one emollient from 3% to 7% and the emulsifier from 3% to 6%. The emulsion was prepared at 70°C and the thickener was added at 50°C. Viscosity measurement, droplets size and stability were analyzed 48 hours following the preparation. In the final emulsions, in terms of viscosity and stability to centrifugation, the glucomannan-based blend was is the parameter with the strongest impact. As for the droplets size, it was impacted the most, thus in a smaller extend, by the emulsifier concentration. Moreover, a synergistic effect between the emulsifier and thickener was monitored on the droplets size parameter while the concentration of squalene proved little influence. Finally, the optimal concentration of glucomannan-based blend to ensure system stability was determined at 1.2%. In conclusion, conducting an Optimal design allowed to model the effect of the thickener in formulation as well as the interactions between the monitored ingredients.