Study by: C. Tournier, C. Villatoro, A. Meacham, M. Fredericq

ABSTRACT: The monitoring of odours released from cosmetic products is a complex task. This paper gives an overview of state of the art sensory and analytical approaches.

The human sense of smell has been underestimated for a long time. However, recent research shows that it is closely connected to emotions, memories, approach, and avoidance and also, evaluative judgment. Thus, the scent of a product can have a significant impact on consumer’s product experience. Consumers pay more and more attention to scents, and to a healthy environment. Often the presence of malodours is perceived as compromised hygiene or even as health threats.

The increasing use of highly functional cosmetic products reflects how much consumers care about their health, their appearance, and they also request longer-lasting protection against body odour formation. Sensenet assists producers and designers of consumer goods to improve the sensory experience associated with their product, using scientific and reproducible methodologies to measure odours. The result can help R&D to optimize the product, support quality control and also be used by marketing for example as claim support.

There are different possibilities to measure the performance of the olfactive signature of a consumer product: sensory and analytical odour measurement techniques and also combinations thereof.

Sampling

Before odour measurement, product’s sampling is a crucial stage. Sampling is highly dependent on the product segment, the product itself, and the objective of the study.

In many cases, it is important that the testing environment is as close as possible to real consumer behaviour and product usage. For certain product segments, standards have been developed (e.g., deodorant testing according to ASTM-E-1207-09) but for all products, it is advisable to develop and perform individualized sampling strategies which are tailor-made to the product or material to be tested.

Thus, an internally developed tool, so-called Scent sample, allows sampling cosmetic products headspace on the surface skin or on hair (Fig. 1).

Human Olfactory Analysis

When performing odour related measurements, it is very important to understand fundamentals of the human sense of smell as well to know the detection capacities of the chosen analytical detector. As of now, there is no analytical tool that can replace the human completely.

A characteristic measure is the odour threshold concentration, which by definition is the concentration where an odour can be detected with a probability of 50 %. For measuring odour threshold concentration, the method of olfactometry is used worldwide (Fig. 2).

An olfactometer comprises a sophisticated system which dilutes odour samples with neutral air and presents them to a test panel for assessment. To standardize such measurements the guidelines and norms of EN 13725 are to be applied. The odour concentration is often expressed in the so-called odour units.

This parameter is useful to describe the odour impact of products. It can be used to measure the odour reduction of malodours or longevity fragrances. However, odour concentration does not correlate directly with the odour perception. For such measurements, other sensory methodologies have been developed.

Opening a product container or the application of a product onto skin releases volatile compounds, which can be often perceived instantly. To assess the odour in a reproducible way, the most common parameters measured are intensity and hedonic tone. It is a challenging task to determine these on an absolute scale since intensity and hedonic tone cannot be judged independently.

Humans tend to underrate the odour intensity when it is pleasant and would overrate it when it is a malodour related stimulus.The standardization of such measurements is very important. The VDI 3882 allows the rating of intensity on a 7 points scale by answering the question “How strong is the odour?”, while the measurement of hedonic tone, which can be performed at the same time, answers the question of “How pleasant is the odour?”.

Depending on the information required, this can be done with trained expert panels or with representative panels. Beside intensity and hedonic tone, it is also possible to focus on the odour character.

One of the most demanding tasks is to establish a sensory description of the odour character of an olfactive signature. It requires extensive training of expert panels prior to doing a sensory odour description.

Sensenet has developed an internal methodology to train panellists and assess odour description based on the learning of a framework containing about 50 referents from different chemical and smelling families (Fig. 3).

This reference was set up from the statistical treatment of the olfactory description of more than 100 odourant molecules by a naivepanel (about 35 people) (Fig. 4).

As a very important aspect of sensory odour measurements, it is necessary to highlight the need of consistent smelling.

Even evaluation from the smelling strip has to be learned and trained.

To facilitate consistent smelling Sensenet uses a PureSniff device: This is an instrument which presents the headspace over a sample in undiluted form when a panellist activates a switch.

It is a universal tool for preparing and presenting the headspace of a product in its pure form (Fig. 5).

The assessing of odours by panellists is fast and allows capturing sensory related information based on human perception, provided to have appropriate screening and training protocols in place.

Sometimes, the measurement of molecular-based information is also mandatory for revealing important facts, which determine the olfactive signature performance over time.

High-end Molecular Spectroscopy can be Linked to Human Perception

Over the last decades, Molecular Spectroscopy methods to analyze headspace compositions have evolved tremendously. Today’s GCMS/TOF instruments can detect molecular traces at concentration levels of 100 times smaller than standard GC-MS Instruments. Olfactive signatures, especially when they contain natural ingredients, reveal high complexity.

The combination with the human nose as a complementary detector allows recording the GC-Olfactometry trace.

Linking the molecular information from GCMS/ TOF with the perceived odour, allows a detailed understanding of the key odour impact molecules present in the product headspace. With this analysis, it is possible to identify molecules responsible for odour distortion (Fig. 6).

Case Studies:

Case Study 1: Hair Products

Some hair products are characterized by unpleasant odours during application. So formula developers search to improve the olfactive perception of this kind of products.

• The first step was to run GC-Olfactometry analyses to detect and characterize compounds responsible for unpleasant smells, to obtain molecular information to develop then fragrances that can mask them.
• The second step was about the validation of the global perception of hair product containing the developed fragrances.
• Hair products have been sampled on real strands of hair using Scent sampler, before intensity, hedonic tone and odour description assessment by trained panellists with PureSniff device.

Case Study 2: Deodourant

More and more cosmetic companies try to find natural substitutes to aluminium salt in deodorants. A sensory protocol can allow to screen and evaluate the efficiency of these potential new active agents.

• The sampling was done, adding artificial on raw material in Nalophane^® bag (inert material) at 32 ° C.
• Odour concentration was then the parameter assessed at different time points (2h, 34h).
• The efficiency was calculated compared to the odour concentration of the artificial sweat only.
• The best candidate can after be tested according to an in-vivo sniff test (intensity measurement according to ASTM-E-1207-09)

Case Study 3: Perfumes

The long-lasting time of perfume is an important parameter in product development., New technologies are developed to improve this parameter. This is the case of a polymer that allows obtaining a perfumed gel with a long-lasting high time.

The objective of this study was to evaluate the efficiency of the polymer to increase the long-lasting time of a commercial perfume.

• Different polymer concentrations in perfume were tested.
• Odour concentration of perfume with the polymer has been quantified at different time points to obtain a decay curve over time and compare it with decay curve of perfume only. Intensity, hedonic tone, and odour description have also been assessed by a trained panel to check that polymer didn’t impact the global perception of the initial perfume over the time.

The Odournet Group, with its dedicated brand Sensenet, has in-depth expertise and a full range of best in class analytical and sensory measurement options to study the performance of olfactive signatures.

Conclusion

The monitoring of the olfactive signature released from perfumed products, and in particular from cosmetic products, is a complex task.

The described methods can be individually applied on the most various test designs, depending on the question to be solved. On the other hand, a high standardization in each step of the complete process of odour measurement (e.g.sample preparation, sample evaluation, panel selection, and training).