Relation of sensory analysis and rheology of cosmetic materials
Emulsions as for instance body lotions represent one of the most important groups of cosmetic products. Market success is not only governed by their properties fulfilling research expectations, it is also customer identified sensory attributes that can dominate. This implies that sensory analysis significantly participates in characterization of the individual products. The sensory panel members evaluate such attributes as ease of dispensing, spreadability on a hand, spreadability on a face, feelings during rub in, residual feeling on the skin after absorption, etc. They also consider any unpleasant feeling concerning sensory attributes that can adversely influence the attitude of consumers to a product regardless of its possibly very good quality from the cosmetic viewpoint.
The problem is that an evaluation of sensory attributes can be both financially expensive and time consuming. Moreover, with even an almost negligible change of the individual ingredients it is necessary to repeat the entire evaluation process once more. This raises a question as to whether in some cases this process could be substituted to a certain extent by alternative methods that demonstrate greater financial and time efficiencies.
Such approach can be connected with the application of instrumental analysis. Its usage does not and cannot cover all aspects of sensory analysis, however some selected descriptors can be evaluated relatively simply and invariantly to the assessors’ level. The rheological analysis is such a candidate and exhibits three positive features: It is relatively cheap, very fast, and inevitable for a proper description and design of a manufacturing process. The rheological magnitudes, such as shear viscosity, are possible to describe empirically and the parameters (respectively their numerical values) of the applied rheological models can be correlated with sensory attributes.