42 SPC September 2014

ODOURNET

The monitoring of the scent-

signature released from

cosmetic products is a

complex task. Dr. Hansruedi

Gygax gives an overview of

state of the art sensory and

analytical approaches.

The Odournet Group, the

largest team of experts in

consultancy for environmental

odour assessments and

olfactory product and material

testing has the most complete

capacities for providing

services focused on sensory

and analytical odour

measurement techniques and

also combinations thereof.

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, which has been

recently described by D.

McCamlie in his article about

Malodour Management in the

context of sweat formation.

A choice of standardized

testing options:

There are different possibilities

to measure the performance of

the scent-signature of a

consumer product. Also, in the

case of deodorants and

antiperspirants, there are

methods to monitor the build-

up of malodour such as sweaty

notes over time. It is very

important to select the method

carefully in order to provide

meaningful answers to the

product developers. The odour

measurements can be targeted

to monitor scent-signature

stability over the products

shelf-life or measurements to

support and document product

claims. In many cases, it is

important that the testing

environment is as close as

possible to the real consumer

behaviour and product usage.

Another well-known

phenomenon is the formation

of malodours, which can for

example be due to impurities

in raw materials. For all

sensory odour measurements,

it is very important to have

appropriate screening and

training protocols in place.

Analytical vs. Sensory

Measurements

When performing odour

related measurements, it is

very important to understand

fundamentals about the human

sense of smell as well to know

the detection capacities of the

chosen analytical detector. 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%. Public

domain information about

sensory threshold

concentrations indicates a

large variability. Very often

malodour key components

have threshold concentrations

far below nanogramm per litre

air. Most of state of the art

analytical detectors at such

concentration levels will only

measure noise. This fact

underlines the importance of

including the human nose as

detector.

Dynamic Olfactometry –

Determination of Odour

Units and Odour Threshold

concentrations.

For measuring odour threshold

concentration, the method of

olfactometry is used

worldwide. An olfactometer

represents a measurement

system which dilutes odour

samples with neutral air and

presents them to a test panel

for assessment. Components

influencing the final panel

results are known and divided

into the three categories: the

olfactometer measurement

system (dilution system), the

assessors and the odour

laboratory. 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 (the

measured dilution facture until

SCENT-SIGNATURESAND HOW TOMEASURE THEIRPERFORMANCE

Figure 2: Olfactometer TO8 by Odournet

Figure 1: Threshold measurements, here a representation of data published by Nagata (2003), show the

immense span from less than 10-6 ppm up to threshold values of over 1000 ppm (a span of 1:10’000’000’000).

Usual analytical detectors would demonstrate a dynamic sensitivity range of 1:10’000. Commercial FID/PID

and e-nose type of sensors reach their sensitivity limits below 0.1 to 0.01 ppm, more sensitivity is reached

with quadrupole MS detectors. GC-MS TOF reaches the lowest sensitivity. The figure demonstrates that a

separation technique (like GC) combined with the human nose as detector is able to go below state-of the art

analytical detection limits. Figure prepared using a graph by Dr. Peter Boeker, University of Bonn.

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September 2014 SPC 43

ODOURNET

the threshold is reached). The

parameters are useful to

describe the odour impact of

raw materials in a mixture and

also to study the longevity of a

scent-signature during its

application on skin. Odour

units can not directly be linked

to perceived intensity. For

such measurements different

sensory methodologies have

been developed.

Odour intensity and hedonic

tone tests

Opening a product-container

or the application of the

product onto skin releases the

volatile compounds, which can

often be 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 point 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

record odour acceptance or to

focus on the odour character.

One of the most demanding

tasks is to establish a sensory

description of the odour

character of a scent-signature.

It requires extensive training of

expert panels prior to do a

sensory odour description.

Naïve panellists, however, can

do a so-called polarity profile,

which uses pairs of adjectives

to describe an odour.

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

Odournet has developed the

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

and thus presents the scent-

signature of a product in its

pure form.

The assessing of scent-

signatures by panellists is very

fast, and allows capturing

sensory related information

based on the human

perception. Nevertheless the

measurement of molecular

based information is

mandatory for revealing

important facts, which

determine the scent-signature

performance over time.

High-End Molecular

Spectroscopy can be linked

to human perception.

Over the last decades,

Figure 3: Odour parameters

Figure 5: PureSniff II by Odournet

Figure 4: Polarity Profile

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44 SPC September 2014

ODOURNET

Molecular Spectroscopy

methods to analyze headspace

compositions have evolved

tremendously. Today’s GC-

MS/TOF instruments can

detect molecular traces at

concentration levels of a 100

times smaller than standard

GC-MS Instruments. Scent-

signatures, especially when

they contain natural

ingredients, reveal a high

complexity. The combination

with the human nose as

complementary detector,

allows recording the GC-

Olfactometry trace. Linking the

molecular information from

GC-MSTOF with the perceived

intensity and perceived odour

quality, allows detailed

understanding of the key

odour impact molecules

present in the scent-signature.

With this analysis, it is possible

to identify molecules

responsible for scent-signature

distortion.

Innovative Headspace

monitoring by GC-IMS

Very recently an interesting

combination of analytical

technology became available.

While IMS has been used

successfully for fast detection

of airborne molecules, it had

its main application to detect

traces of plastic explosives at

airports, to find traces of

drugs, or for military

applications such as the

detection of warfare agents.

The combination with GC

separation opens up a new

technique to visualize the

presence of scent-signatures

in a 2-D Fingerprint. The

headspace of a product is

collected and injected in a

short GC- multi-capillary

column. When eluting from the

column, the molecules are

ionized, and analyzed in Ion

Mobility Drift-tube. Within a

short sample processing time

(few minutes), the 2D

fingerprint is recorded and can

be analyzed and compared in

various ways. Presence or

absences of key components

of a scent-signature are seen

immediately and sophisticated

data processing methods

allow a classification of

samples, as well as a

quantification of molecules of

interest.

GC-IMS in particular can be

used to observe the 2D

fingerprint over time to study

the dynamic changes of a

cosmetic product or perfume

after its application onto skin,

or to compare the

similarity/difference of

products. And last but not

least, it is possible to visualize

the formation of off-notes

during the product’s shelf-life.

Conclusion

The monitoring of the scent-

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) is the key for

reliable and repeatable

results. The Odournet Group

has in-depth expertise and a

full range of best in class

analytical and sensory

measurement options to

study the performance of

scent-signatures.

Figure 6: GC-Olfactometry

Figure 7: Heat map visualization of a GC-IMS measurement; © GAS-

Dortmund

Figure 8: PCA analysis based on the results of the GC-IMS: Odour

comparison of a reference (sample 8) with various samples, finding

which samples are very similar to the reference and which are not

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