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.

There are many parameters on which the panellists can evaluate an odour. The most common are the odour intensity, hedonic tone, odour character and odour concentration.

These first three parameters can all be determined by so-called ‘direct sniffing’. Panellists evaluate the odour samples undiluted and blindly, directly from Nalophan bags or other specific recipients. The odour intensity can be assessed for the overall odour of a sample, but also for specific odours. For example, when a cleaning product with a fragrance is used it is often interesting to ask the panellists for the fragrance and malodour intensities separately.

Panellists should be trained in the usage of odour intensities scales with reference odours. Reference odours are also used to train panellists in the odour character description. For example, while the odour of cigarette smoke might be more easily described by most people, the subtle notes of a fragrance require more training. The hedonic tone shows the pleasantness of an odour. As this is a subjective impression, panellists cannot be trained in this parameter.

The parameter of odour concentration is measured with the use of an olfactometer. The aim of this method, known as dynamic olfactometry, is to determine how often an odour can be diluted until the panellists are just able to detect the odour, ie, the detection threshold. This is expressed in an amount of European Odour Units, the OUE. A higher OUE means that an odour has a lower detection threshold and is thus stronger. By measuring before and after cleaning conditions, the odour reduction efficacy can be expressed as a percentage in OUE reduction.

Important to note, is that the odour concentration looks at the overall odour. This means that when a fragrance is added to a cleaning product, the amount of OUE directly after cleaning might be higher than before cleaning, resulting in a negative odour removal efficacy while the odour might have become more pleasant. In cases with perfumed products, is it therefore important not to consider this method (dynamic olfactometry) but measure the malodour and fragrance intensities as well as the hedonic tone.

Instrumental odour analyses

Instrumental analyses are used when the chemical composition of a sample is of importance. This can be the case when there are concerns about health and safety. Chemical analyses are also used during new product development. After all, in order to create new techniques to remove specific odours one needs to know which chemical components are the relevant ones. Often used methods are GC-MS and GC-IMS.

The GC-MS method consists of gas chromatography (GC) and mass spectrometry (MS) analysis. Usually, the odour samples are collected in thermal desorption tubes for further analysis. Desorption of the volatile organic compounds present in the odour sample is done with high temperature (eg, 280-300°C), followed by a low temperature adsorbent trap (eg, 0-5°C) and another heating round (eg,, 300-350°C) to release the adsorbed volatile compounds into the gas chromatograph (GC) column. In the GC column, the volatile organic compounds are separated based on their interaction with the GC column and physical-chemical properties.

After going through the column, the volatile compounds arrive at the MS, whose measurements are transformed into a chromatogram. In the chromatogram, the volatile compounds are represented as peaks showing the intensity and time of detection of the signal. Based on the information of these peaks, the different volatile compounds can be chemically identified and quantified. A GC-MS analysis results in a list of identified chemical compounds and their chemical concentrations.

GC-IMS is often seen as an alternative method to GC-MS, it consists of gas chromatography and ion-mobility spectrometry. The GC-IMS provides less detailed information but is much faster and thereby allows for continuous sampling. Thanks to the relatively small size of the GC-IMS, it can be brought to a sampling location for direct measurements.

The volatile compounds at the GC-IMS inlet are separated by a GC column, after which they are ionised, drift into an electrical field and are separated based on their charge, mass and shape. After going through the drift region, the volatile compounds reach the detector which transforms the data in a so called ‘fingerprint’. The fingerprints of different samples can be compared, for example to monitor a room’s air over time.

Selection of the analysis method

As there are many different analysis options, it can be difficult to select the best analysis for specific research questions.

For the cleaning product against cat urine odour, a study to make an odour claim on the packaging makes sense. In order to claim odour reduction, a sensory odour analysis is required. One option would be to work with odour concentration analyses for the untreated condition, the new product cleaned condition and the reference product cleaned condition. By comparing the odour concentrations of these different scenarios, it is possible to calculate the odour reduction percentage which can be achieved by using the anti odour product.

If one of the products is perfumed, using only odour concentration would not be sufficient. The odour concentration is about the strength of an odour, and adding a perfume can increase the amount of odour. The odour reduction percentage might then become negative, while the odour did become more pleasant. In such cases, it is important to either include the hedonic tone or to switch to odour intensity of the malodour and perfume odour separately.

To determine the efficacy of odour cleaning services, both sensory and instrumental analyses could be used. The sensory analyses, such as odour intensity for malodours, hedonic tones and odour characters, can be used to show if there is a difference in the odour before and after cleaning. In cases with chemical spills, it can be very important to also assess the safety of the resulting odour.

After cleaning, the indoor air should not exceed safety levels for specific chemicals. GC-MS can be used to detect and quantify a large range of chemicals. For some chemicals, such as formaldehyde, specific cartridges can be used to quickly quantify the amount.

Conclusion

Typical odour studies in the cleaning product industry focus on quantification of the odour reduction efficacy of products and services. Sampling methods are highly individual and are based on the specific product or service. The evaluation methods also depend on the research questions. In order to create a new anti-odour technology, insight in the chemical composition of specific malodour can be needed.

This can be done with the use of instrumental analyses, such as GC-MS and GC-IMS. In order to make a claim about the efficacy of a finished product or service in terms of the perceived odour, sensory odour analyses are needed.