New scaling method for off-odours in packaging headspace developed

07 Mar 2011

New research claims to have developed a scaling sensory method to assess perceived off-odour intensity in package headspaces.

Scientists from Denmark said the method includes a raft of features - from the section and monitoring of a sensory panel to the evaluation of different scaling techniques. The process can, over a period of time, realise a “reliable…and fairly reproducible method for the evaluation of off-odours” in packaging headspaces said authors Wender L.P. Bredie et al.

They said the objective evaluation of packaging headspace smells in food and drink packaging was important as off-odours negatively influence consumer perceptions. The research was published in the Journal of Sensory Studies.

Method

The study – Development of a Sensory Test Method for Odour Measurement in Packing Headspace – found that 1-butanol proved to be a “reliable” reference scale because it was a “well-described and safe odour” and also fused frequently due to its “accepted repeatability and easiness of handling”.

Other elements included the selection of eight panellists with a questionnaire and the “Sniffin’ stick test and the use of three types of scales; a 15-cm line, a colour-graded brightness line scale and a colour-graded brightness category scale.

The trio of response scales for odour intensity were tested and compared using 1-butanol as a reference odour.

“The scales included two different cross-modality scales, where the perceived odour was scored on a colour-graded brightness scale,” said the group. “These scales were compared to the responses on an unstructured intensity scale. It was investigated if the cross-modality scaling could improve the reliability of the off-odour intensity measurements.”

Carton packs

The eight packages tested were of a laminated carton type for fluid foods, with the same basic structure of polyethylene as inside and laminate as outside layers, aluminium foil as a light and gas barrier layer, and carton as a stiffness layer. The packages all had a headspace above the product.

All were tested with drinking water as filling material, while three were additionally tested with air only. Tests with water-filled packages were believed to closely mimic a real-life consumer situation of opening a container and observing an odour in the headspace above the product.

One of the researchers, Lars Kristoffersson, works for Tetra Pak Packaging Solutions.

The scientists carried out a number of tests and compared means and standard deviation data to determine which scaling method was most suitable for rating the 1-butanol odour intensity.

“The two line scales tended to give a smaller standard deviation than the colour brightness button scale as the colour brightness line scale had 22 incidences of lowest standard deviation, the line scale 20 incidences and finally the button brightness scale had 13 incidences of lowest standard deviation…,” said the research.

Conclusions

The study said it had developed a scaling method which converted the perceived off-odour intensity in packaging headspace into 1-butanol concentrations in parts per million (ppm).

The 1-butanol scale showed good repeatability and the scaling type did not affect its odour intensity which suggested that all three scales were fit for purpose.

Using a brightness scale appeared to strengthen repeatability. However, the study found that the colour brightness line scale was the most repeatable, with the colour brightness button scale the least repeatable.

The group also found that day-to-day variations influenced odour intensity measures which, the said, “proves the importance of making a reference scale on every test day”.

The advantage of the system is it allows the conversion of an intensity judgement of a packaging headspace to a physical intensity scale of 1-butonal and therefore “provides a valuable reference for comparing different package assessment over time”, said the study.

Source: Journal of Sensory Studies