NIR spectroscopy as a powerful and non-invasive method for food quality control

Consumers expect products of controlled quality, origin and free of harmful ingredients to reach their table. Last but not least, producers and manufacturers are anxious to protect the authenticity of their brand by defining high internal standards to strengthen their market position.

These demands require the introduction of advanced technologies to provide controlled food products all over Europe.
One of these premium products is Parma ham, which is taken as an example to show the implementation of high quality control for this DOC product.

The Stazione Sperimentale per l'Industria delle Conserve Alimentari together with the Instituto Parma Qualità in Parma Italy, introduces an elegant application for testing premium Parma raw dry-ham using Near Infrared Spectroscopy (NIR). The determination of different chemical parameters is one of the main quality control aspects in Parma ham production. It serves to check if the target figures for premium ham given by the Consorzio del Prosciutto di Parma are respected, so that only highest quality products will reach the consumers’ tables.

A Buchi NIR-spectrometer is used to analyse the ham in the laboratory. The hams are cut into two pieces and from one half of the muscle Biceps femoris a one centimetre thick slice is taken and minced in order to determine the following parameters: sodium chloride (salt), moisture, protein, extractable nitrogen (N) in trichloroacetic acid (TCA), and the proteolysis index.
A students t-test (p > 0.05%) shows that conventional techniques and NIR measurements give similar results for all parameters. Considering the quick output response directly obtained by the Buchi NIR system during the production process, this technique achieves a great effort in cost and time savings.

Besides the rapidness, the possibility to perform non-invasive analytics on food is a major advantage of the NIR technique founded on the properties of the NIR radiation, or to be more precise, on the physical nature of the excited vibrational transitions. The wavelength region between 10 000 and 4000 cm-1 is characterised by a weak degree of absorption. Thus, a high ratio of the incident light is reflected from the solid surface after interaction with the ham and can be collected and analysed in the so-called reflectance mode.

Altogether, five parameters are determined in parallel. The Consorzio del Prosciutto di Parma has defined certain limits for these parameters to ensure that the product quality and brand authenticity of Parma ham is maintained.

How does it work?

Using an NIR experiment, the gathered spectral information is linked to one or several properties. Therefore, reference values have to be checked independently by a different analytical technique like Kjeldahl, extraction or chromatography. These data can be used to build up a calibration set, which is consulted by a chemometric software to predict the properties of unknown samples. This is referred to as the validation of the calibration. This method enables to determine several parameters at the same time by only measuring one spectrum of a sample.

An example: One of the most important parameters in ham quality control is the proteolysis index.

As the proteolytic cleavage reduces the amount of intact protein over time, the proteolysis index is an indicator of the maturing process of Parma ham. It is defined as the ratio of non protein nitrogen fractions, such as aminoacid- and oligopeptides, to the overall nitrogen content.

The table below summarises important parameters derived from the Buchi NIRCal software. They show the consistency of calibration data (SEC) and routine results (SEP).

SEC: Standard error of calibration, SEP: Standard error of prediction

According to the statistical analysis, there is no significant difference between the data obtained by NIR spectroscopy and the reference values.

An alternative to the measurement using minced ham and petri dishes would be the application of a fibre optic probe. This would provide the benefit that the valuable meat has not to be impaired. Although this method leads to slightly worse results and higher statistical errors, the measurements can be speeded up as no additional sample preparation is needed.

What is the benefit?

The quality relevant parameters of Parma ham can be monitored easily during the production process, even on a high number of samples. There is no need for time consuming and wasteful preparation and perhaps most important: the end-product is neither harmed nor destroyed during analysis. Brand authenticity and the premium quality are ensured and the ham is immediately ready for distribution: This means quality control at its highest level.

References: All data were taken from the following references:

Applicazione della spettroscopia NIR con sonda fibre ottiche per determinare la composizione del prosciutto crudo stagionato DOP.

Industria Conserve, 80, 277 (2005)
Marta Bellatti 1, Giuseppe Ferrari 2, Monica Reverberi 3

1. Stazione Sperimentale per l`Industria delle Conserve Alimentari, Parma
2. Büchi Italia S.r.l., Assago (MI)
3. Istituto Parma Qualità, Parma