Recycled PET packaging: olfactive quality evaluated by sensory analysis

The use of human sensory panel is the historical way to evaluate the olfactive quality of specific products but, despite a rigorous training, the response of the individual to a specific sample can be very heterogeneous. Thus, a good evaluation should at least involve a certain number of panelists, usually 12.

In Alfatestlab we can provide an objective and neutral olfactive evaluation thanks to sensory analysis through an electronic nose (Heracles – AlphaMOS): the analysis is a highly selective, rapid and sensitive gas chromatograph combined with a powerful data treatment software that can replace a sensory panel for routine quality control, product development, benchmarking and shelf life studies.


Case study: recycled PET packaging analysis

We have been asked by a packaging manufacturer to compare three different batches of recycled PET pellets (A, B and C) with pure PET reference (named REF), used to produce plastic films. In Figure 1 is shown the Principal Component Analysis (PCA) that provides an “odor map” for 3 aliquots of each batch (A, B, C and REF).

Figure 1 – Odor map obtained from the Principle Component Analysis (PCA) of recycled PET pellets (A, B, C) and pure PET (REF).

Both x- and y-axis show the variability of the samples: PC1 (x-axis) represents the higher variability, PC2 (y-axis) the second higher variability: closer the samples the less differences between them, and more similarity. In this specific example, Sample A is the more similar to the reference, while Sample B is the more different. The peak vectors of the main discriminant volatile compounds have been included in the PCA, as shown in Figure 1b: they are pointing toward the assays that contain the highest quantity of the corresponding compound.

The most discriminant compounds typical of these samples were potentially identified using a specific database (AroChemBase) and reported in Figure 2: for all recycled PET – samples A, B and C – toluene appears to be the most discriminant volatile compound respect to the reference, the higher content being measured for batch B. Batch C shows mainly a higher content of hexanal, 2-undecenal and 1-(2-thienyl)-ethanone, respect to batches A and B. These volatile products are also discriminants respect to the reference.

Figure 2 – Histogram of the most discriminant volatile compounds for recycled PET pellets (A, B, C) and pure PET (REF).


In general, this analysis can easily help you identifying compounds that are “too different” from a reference compound by defining a graphic reference area (green) and a fail area (red), as shown in the examples reported in Figure 3.

Figure 3 – Examples of graphic representations obtained from different data treatment procedures.



The sensory analysis by electronic nose is an efficient tool to evaluate the olfactive quality of your products in a variety of industries, not only packaging: food and beverage, plastics, cosmetics, etc. and is well suited for benchmarking and shelf life studies, thanks to the different possible treatment data procedures. The identification of the most discriminant volatile compounds allows to target your trouble shooting processes and accelerate product development or formulation. Contact us to discuss your sensory analysis needs and discover how we can help!


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AlfatestLab is a contract analysis laboratory that provides you with results you can trust, thanks to decades of experience on analytical techniques and their applications.

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