A Product Engineering Approach: Diffusion and Performance of Fragranced Products

Product Engineering Approach for the Design of High Performance Fragranced Products

Miguel A. Teixeira and Alirio E. Rodrigues*

LSRE -- Laboratory of Separation and Reaction Engineering, Associate Laboratory, Dept. of Chemical Engineering, Faculty of Engineering of University of Porto

Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

Abstract

Chemical Product Engineering has emerged over the last decade as a new paradigm on Chemical Engineering.^{1, 2} In fact, this is an answer to a global change in the chemical industry economy: in the past driven by technological expansion for the large production of commodities, towards a market-driven production of high added-value, specialty and performance products as happens today.^{2, 3} The relevance of introducing perception, and namely consumer perception, in the design of chemical products has been recently highlighted as an important step for product design. Among the different types of perception, those related to chemical perception (chemosensory) and namely taste and olfaction are still difficult to work with. This is due to the complexity of the process of olfaction at the biochemical level.

Fragrances are presented in countless products we deal with everyday like perfumes, shampoos and soaps among many others. In fact, more than three-quarters of toiletries and household products contain a fragrance in its composition. However, the design of fragranced products is still a combination of art, technology, and some scientific knowledge, although the former predominates at the industry.^{4, 5}

In order to reduce subjectivity and empiricism in this field, we have developed an integrated theoretical model to assess the performance of fragrances considering the release and diffusion processes together with the predicted odor intensity over time and distance from the source. In order to achieve that goal, our model combines different scientific fields: Thermodynamics, Transport Phenomena, and Psychophysics into a common product - fragrances. This approach is within Product Design or Engineering, which in this case is applied to Perfume Engineering as shown in Figure 1.

Figure 1 - Our vision of what is Perfume Engineering: the integration of concepts from different fields (Thermodynamics, Transport Phenomena, and Psychophysics) in order to improve the design and development of new perfumed products.^4

Within this line of though, we can simplify fragranced products to a mixture of N fragrance raw materials diluted in a suitable matrix (a liquid solvent, a water/oil emulsion among others) at some concentration which can be sprayed on the skin or the clothes by the customers. After application of the product, the process of perception proceeds as follows: i) fragrances start to evaporate at different rates depending on their physicochemical properties and those of the mixture and, then, ii) they diffuse through the surrounding air until reaching the nostrils of consumers or other people around; and, finally, iii) fragrance molecules will eventually reach the human nose and above some concentration (known as the odor threshold) they will be detected and recognized with a specific intensity and character. Thus, our approach for Perfume Engineering combines knowledge from Chemical Engineering (Thermodynamics and Transport Phenomena) which can describe steps i) and ii), together with models from Psychophysics for step iii) as shown in Figure 2.^6-9

Figure 2 -- Schematic representation of our odor model for the perception of fragranced products.

Overall, our model will allow predicting and mapping the perceived odor elicited from any mixture of fragrance ingredients, thus reducing significantly the number of trial and error experiments which are expensive and time consuming for the Flavor & Fragrance industry.

In this work, we present a theoretical approach and experimental validation of our model for the step of fragrance diffusion together with the assessment of product performance using similar properties to assess it as the industry (like impact, tenacity, diffusion and volume parameters).^9 In this way, concentration profiles were experimentally measured in a diffusion tube, similar to the Stefan tube, and predicted with a model for pure fragrance chemicals, binary, quaternary, and multi-component (up to 11 chemicals) mixtures. A very good agreement between our purely predictive model and experimental concentration data was observed. Fragrance concentrations in air were then converted into odor intensities using models from psychophysics, making it possible to evaluate the evolution of the odor with time and distance using a performance plot. Accordingly, the performance of these mixtures was modeled and experimentally validated, which constitutes a landmark for fragrance design.

It was observed that the performance of a fragrance depends on the intrinsic properties of its constituents, but also on their molecular interactions in the liquid solution. Thus, the evaporation rate of each fragrance remains a function of mixture's initial composition (x_i), molecular interactions (activity coefficient, �µ_i), and temperature (T) but it is simultaneously dependent on the physicochemical and psychological properties of each fragrance chemical (diffusivity, saturated vapor pressure, molecular weight, ODT, and power law exponent). Another important conclusion to draw from this work is that it is possible to measure and predict the performance of a perfumed product using perfumery terminology and a theoretical model to assess the perceived odor over time and distance from the source. Finally, it is expected that this work might contribute to reduce the time needed for the design of perfumes and fragranced products in the pre-formulation step and the reduction of the consumption of raw materials. Altogether, that will contribute to decrease production costs.

References

1. Cussler, E. C.; Moggridge, G. D., Chemical Product Design. Cambridge University Press: Cambridge, 2001.

2. Wesselingh, J. A.; Kiil, S.; Vigild, M. E., Design & development of biological, chemical, food and pharmaceutical products. Wiley: Chichester, U.K., 2007.

3. Cussler, E. L.; Wagner, A.; Marchal-Heussler, L., Designing Chemical Products Requires More Knowledge of Perception. AIChE Journal 2010, 56, (2), 283-288.

4. Teixeira, M. A.; Rodriguez, O.; Gomes, P.; Mata, V.; Rodrigues, A., Perfume Engineering: Design, Performance & Classification. Elsevier: Oxford, UK, 2013.

5. Sell, C. S., On the unpredictability of odor. Angewandte Chemie-International Edition 2006, 45, (38), 6254-6261.

6. Teixeira, M. A.; Rodriguez, O.; Mata, V. G.; Rodrigues, A. E., The Diffusion of Perfume Mixtures and Odor Performance. Chemical Engineering Science 2009, 64, 2570-2589.

7. Teixeira, M. A.; Rodriguez, O.; Mata, V. G.; Rodrigues, A. E., Perfumery Quaternary Diagrams for Engineering Perfumes. AIChE Journal 2009, 55, (8), 2171-2185.

8. Teixeira, M. A.; Rodriguez, O.; Mota, F. L.; Macedo, E. A.; Rodrigues, A. E., Evaluation of group-contribution methods to predict VLE and odor intensity of fragrances. Industrial & Engineering Chemistry Research 2011, 50, 9390--9402.

9. Teixeira, M. A.; Rodriguez, O.; Rodrigues, A. E., Diffusion and Performance of Fragranced Products: Prediction and Validation. AIChE Journal 2013, (accepted).