Towards satisfying performance of an O/W cosmetic emulsion: screening of reformulation factors on textural and rheological properties using general experimental design.

OBJECTIVE: Consumers' demand for improved products' performance, alongside with the obligation of meeting the safety and efficacy goals, presents a key reason for the reformulation, as well as a challenging task for formulators. Any change of the formulation, whether it is wanted - in order to innovate the product (new actives and raw materials) or necessary - due to, for example legislative changes (restriction of ingredients), ingredients market unavailability, new manufacturing equipment, may have a number of consequences, desired or otherwise. The aim of the study was to evaluate the influence of multiple factors - variations of the composition, manufacturing conditions and their interactions, on emulsion textural and rheological characteristics, applying the general experimental factorial design and, subsequently, to establish the approach that could replace, to some extent, certain expensive and time-consuming tests (e.g. certain sensory analysis), often required, partly or completely, after the reformulation. METHODS: An experimental design strategy was utilized to reveal the influence of reformulation factors (addition of new actives, preparation method change) on textural and rheological properties of cosmetic emulsions, especially those linked to certain sensorial attributes, and droplet size. RESULTS: The general experimental factorial design revealed a significant direct effect of each factor, as well as their interaction effects, on certain characteristics of the system and provided some valuable information necessary for fine-tuning reformulation conditions. Upon addition of STEM-liposomes, consistency, index of viscosity, firmness and cohesiveness were decreased, as along with certain rheology parameters (elastic and viscous modulus), whereas maximal and minimal apparent viscosities and droplet size were increased. The presence of an emollient (squalene) affected all the investigated parameters in a concentration-dependent manner. Modification of the preparation method (using Ultra Turrax instead of a propeller stirrer) produced emulsions with higher firmness and maximal apparent viscosity, but led to a decrease in minimal apparent viscosity, hysteresis loop area, all monitored parameters of oscillatory rheology and droplet size. CONCLUSION: The study showed that the established approach which combines a general experimental design and instrumental, rheological and textural measurements could be appropriate, more objective, repeatable and time and money-saving step towards developing cosmetic emulsions with satisfying, improved or unchanged, consumer-acceptable performance during the reformulation.

A combined approach in characterization of an effective w/o hand cream: the influence of emollient on textural, sensorial and in vivo skin performance.

To formulate a consumer-acceptable cosmetic product, numerous demands have to be fulfilled, and as the most important, efficacy (both real and perceived), adequate aesthetic (visual perception) and all sensorial characteristics have to be achieved. In this study, four model water-in-oil creams intended for hand care, varying in one emollient component, were submitted to rheological, sensory and textural characterization, and their efficacy was evaluated in in vivo study on human volunteers. Our results indicate that certain alteration restricted to the oil phase induced a change in all investigated characteristics, showing that each instrumental measurement can be used as a sensitive tool in the characterization of cream samples. Regarding the correlation between physical measurements and certain sensory attributes, it is possible to formulate a product with specific sensory characteristics by using pre-defined rheological or textural parameters. To obtain a complete sensory profile of a cosmetic product, a detailed sensory evaluation should be carried out according to the existing standard practices, which are both time- and money-consuming. However, a modified sensory study could be useful for fast in-line screening along with instrumental characterization of a novel cosmetic emulsion product and could be particularly helpful in the process of distinguishing a single formulation from several differing in one component.