Measurements meet perceptions: rheology-texture-sensory relations when using green, bio-derived emollients in...

Product aesthetics and sensory performance can strongly influence a cosmetic product's acceptance by consumers. However, classic sensory analysis is time-consuming, expensive and does not provide information on the target group's preference. In the previous phase of this project, we had untrained consumers evaluate six cosmetic emulsions based on their aesthetics using a check-all-that-apply (CATA) survey. In this project, our goals were to quantitatively characterize the rheology and textural properties of the six cosmetic emulsions containing green, bio-derived emollients and identify statistical relationships between the consumers' description of products and the instrumental measurements.

Six emulsions were prepared-three with olive oil and three with heptyl undecylenate as an emollient. Four sensory-like attributes, namely firmness, work of shear, stickiness and adhesiveness, were tested using a texture analyser. Rheological characterization included continuous flow testing and oscillatory measurements. Droplet size and stability were also evaluated. Statistical relationships were quantified between measurements in this study and sensory survey results published previously.

The textural and rheological results indicated that the emulsions were different-as designed. The texture and rheology measurements had analogous grouping outcomes to the consumers' discrimination. Emulsions 1 and 2 were the firmest, hardest to spread, stickiest and had the highest viscosity, while Emulsions 5 and 6 were the least firm, easiest to spread, less sticky than Emulsions 1 and 2, and had the lowest viscosity. Emulsions 3 and 4 fell in between the other two groups. Using olive oil instead of heptyl undecylenate as an emollient increased firmness, spreading, stickiness, viscosity and droplet size of the emulsions in every case-when comparing emulsions within each pair. All six emulsions had a shear-thinning behaviour. Viscosity and firmness directly correlated for the emulsions. Emulsions were visually stable at room temperature over the course of 6 months and viscosity remained relatively constant over this period also.

Certain sensory attributes can be reliably predicted with instrumental measurements. Identifying and quantifying sensory-texture-rheology relationships can contribute to achieving appropriate product characteristics tailored to suit market needs.