Sensory and instrumental properties of dark chocolates

K. Dürrschmid, M. Wendelin, G. Schleining, W. Kneifel
Department of Food Science and Technology, University of Natural Resources and Applied Life Sciences, Vienna

Owing to the steadily increasing market potential of dark chocolate in Europe, the sensory as well as the instrumental characterization of this product category has become an important issue in food quality assurance. For this purpose a study was undertaken to examine a selection of five kinds of dark chocolate originating from a well-known Swiss manufacturer. Samples examined differed with regard to their cocoa content (55, 65, 70, 75 and 85 %).

Instrumental analyses were performed to assess criteria like colour, texture, melting and flow behaviour and viscosity. The following sensory methods were used to describe the products in sensory terms:  free-choice-profiling with 39 untrained but instructed students, descriptive analyses with a trained panel and a hedonic acceptance test with 150 consumers. Samples were administered in a coded way within the analytical sensory tests. The acceptance was determined in a non-branded as well as in a branded way.

No significant differences were found among the different chocolates in terms of the breaking energy. However, fracturability and stiffness were significantly different between the 65% and 85% types. The colour (Lab-values) was found to be in linear agreement with the cocoa content. Ranking of the products in terms of viscosity from low to high resulted in the following order: 65, 55, 70, 75, 85 %. These results also match with the sensory description of the melting behaviour. Differences in the melting points were significant albeit subtle. The generalized procrustes analysis of the free-choice-profiling data correlated with the results of the quantitative descriptive analyses. However, it was not possible to get a consistent profile of sensory properties from the free-choice-profiling. Several sensory attributes (e.g. breaking force, bitter, sweet, sour, fatty, melting rate, astringent) were used for describing the chocolates. The results of the acceptance tests indicated, that the cocoa content is negatively correlated with the acceptance of the samples.
Nevertheless, consumers who are reluctant in trying new food, tend to refuse eating chocolate with a cocoa content of ≥ 70 %. Branding of the products affected the evaluation results slightly. In general, the common chocolate eater obviously still prefers the white and milk types of chocolate and not so much the investigated dark ones.