The science of odour

31st of May 2023
The science of odour

Odour plays an important role in the cleaning products industry. Fragrances can be added to products to elicit specific associations and emotions, or to mask a malodour. Specific technologies have been designed to battle malodours such as tobacco and pet odours. Lieke van Genderen at Olfasense tells us more in this two-part report.

The incorporation of a  fragrance or odour reduction technology can be quite a process. There are many fragrances and technologies available on the market, of which the effects can differ based on the formula and application of the product they are being incorporated in. After making a decision on which fragrances and/or technologies are to be used, it is time to create some pilot batches. Such pilot batches typically receive a wide array of testing, part of which can be sensory and instrumental (chemical) odour analyses.

The first step in most analyses is the sample preparation. Depending on the research question, assays can range from a laboratory setting to real life pilot studies. Some examples of test designs related to anti odour cleaners and efficacy determination of cleaning services will be described in this article.

Anti odour cleaner

Cleaning products can be designed to help against specific odour issues, like pet odours. Removing these odours can be a difficult task for consumers, especially for certain types of surfaces such as sofas and carpets.

An example is a cleaning product which has been designed to remove the odour of cat urine from carpets. In order to analyse the efficacy of a product with these characteristics, three different test conditions with cat urine can be created. One condition being the uncleaned carpet, or the untreated condition. The other  conditions are carpets which are cleaned with the new product and with a reference product.

Testing could be done with a synthetic malodour mixture which represent cat urine odour. However, in order to fully understand the odour reduction efficacy of the cleaning product, working with real cat urine will give more insights. Cat urine can be collected by using special fillings for cat litter boxes. The urine of multiple cats should be used. This is not only recommended to get enough urine for the test, but also as the odour will vary naturally and including multiple cats will provide a more representative odour.

The cat urine is then applied evenly to a large carpet tile and left for a few hours. In a real usage scenario the ‘urine incident’ is not likely to be found out immediately, and the cleaning product will thus not be applied immediately. The carpet tile is then cut into even strips for the three different testing conditions.

For the untreated condition, the carpet is not cleaned. For the new product condition and the reference product conditions, the carpet is cleaned according to the use instructions of each product. The carpet tiles are then placed inside three different climate chambers.

The temperature, relative humidity and air flow of the emission chambers can be changed, depending on the environmental conditions for which the product needs to be tested.

After a few hours, or days, depending on the research question, the odour samples are ready to be collected. Samples of the outgoing fixed air flow, which has been blown over the carpet, can be taken from the sampling ports of the emission chamber. The samples can be collected inside Nalophan bags for further sensory analyses and on thermal desorption tubes for further chemical analyses.

Efficacy determination

Cleaning services are not only used for the regular maintenance of buildings; their expertise can also be needed in difficult cases such as after fire damage or spills in production facilities. The removal of cigarette smoke odour after a property or vehicle has been rented is a recurring situation, for which rental companies also require specialized cleaning services.

When assessing the odour reduction efficacy of a cleaning service, at least two conditions have to be analysed. The first condition is the odour of the room/vehicle just before the cleaning has started, the pre-cleaning condition. The second condition is the odour after the cleaning. Multiple ‘after cleaning’ samples can be taken. Directly after the cleaning, the odour of the used cleaning products might be noticeable, creating a masking effect on the malodour. For returning odour issues, taking a sample after a few days can also provide valuable proof.

Taking a sample from a room, or vehicle interior, is often done using the so called lung-method. With this method, a Nalophan bag is placed inside a special sampling container. The Nalophan bag has an open connection towards the rooms indoor air. A vacuum is then created inside the container, resulting in the air from the room being drawn into the Nalophan bag. The duration of the sampling can be varied.

For a more homogenous sample, taking a sample over a longer time is recommended. A sampling time of three replicates of 30 minutes is generally used for environmental odour analyses. After the set sampling time, the Nalophan bags with the odorous samples can be used for sensory analyses. In addition, with the use of a pump, the odorous air can also be sampled on thermal desorption tubes for chemical analyses. It is not recommended to have panellists evaluate odour directly from inside the room, as visual influences and sensory adaptation could then become a problem.

Odour analyses

The sampled air can be analysed using sensory and instrumental (chemical) methods. With sensory odour analyses, trained odour panellists take part to evaluate the odour perception of the test samples. In the case of instrumental methods, the chemical composition of the samples can be determined.

Sensory odour analyses

The first consideration when evaluating the odour of a sample, is the use of an internal or external sensory panel. Internal panels, who are trained odour analysts, often participate in the beginning stages of an R&D process and/or for QA/QC purposes. Most of the cleaning product manufacturing companies have their own internal panels.

In the first stages of new product development, the internal panel can be used to exclude pilot batches due to, for example, a much too weak or strong odour, or an odour character which does not fit with the company or brand. Once the product has been developed, the internal panel can perform regular batch analyses to check that the product continuously meets their quality criteria.

As with most analyses, the internal panel will require regular training to be able to deliver high quality results. In addition to regular training, the olfactory capabilities of odour panellists need to be checked regularly as our sense of smell is known to vary.

External panels, who are trained panellists from independent entities (eg,., testing laboratories) are often used when a higher analysis quality is required, and for impartial claim support of the final products and services. Specialised odour laboratories have access to equipment which has been designed for odour sampling and analyses, and the panellists have been selected and trained according to strict protocols.

• The second part of this report will be published in the June/July edition


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