Handheld Laser Spectroscopy Shows Promise for Rapid Screening of Illegal Dyes in Paprika Powder

In a recent study, a team of researchers at the Leopold-Franzens University in Innsbruck, Austria demonstrated that a portable, handheld spectroscopy device can screen paprika powder for illegal synthetic dye adulteration in the field, potentially giving food safety inspectors and processors a faster first-line tool ahead of laboratory confirmation testing.

The study, which was published in the journal Analytica, evaluated whether handheld laser-induced breakdown spectroscopy (LIBS) can detect and quantify sodium-salt azo dyes, such as Allura Red (E129), Ponceau 4R (E124), and Orange II, added to paprika powder to artificially boost its color.¹

Why is color fraud a problem in the paprika trade?

Paprika is a popular spice that comes in different types based on their heat level.^2,3 It is used in a variety of seasonings and sauces.⁴ The heat level of paprika often dictates the type of dish that it is used in, so it is important that consumers know which type of paprika they are buying.

Because of this, bad actors have taken to mix synthetic dyes into paprika powder to change its appearance and present it as a type of paprika powder that it is not. Current confirmatory testing relies on chromatographic methods performed in centralized laboratories, a process that is accurate but slow and unsuited to on-site or at-line checks during processing or import inspection.¹ In their study, the research team investigated whether their handheld LIBS device can be a rapid screening step to flag suspect batches before they are sent for full laboratory analysis.¹

What did the researchers do in their experiment?

As part of the experimental procedure, the research team spiked paprika powder with the three dyes at 17 concentration levels, from 0 to 6% by weight, across three independent batches.¹ The samples were mixed with an aluminum oxide binder, dried, and pressed into pellets to improve measurement consistency, then analyzed using a SciAps Z-903 handheld LIBS device under an argon atmosphere across a broad wavelength range of 190 to 950 nanometers.¹

One important aspect to this study is how the LIBS device operated. The target dyes, being organic compounds, could not be detected directly. As a result, the research team relied on an indirect signal: sodium emission from the dyes' sodium-salt counter-ions.¹ As dye concentration increased, sodium emission rose correspondingly, providing the primary basis for quantification. The team also observed a secondary, inverse-trending signal from aluminum tied to the binder and plasma behavior, even though the binder proportion remained constant.¹

How was partial least squares regression (PLSR) used in the study?

The research team used PLSR to accurately calibrate the spectral data collected. Depending on the dye, the researchers achieved validation accuracies of 0.83 to 0.92 and calibration accuracies of 0.86 to 0.96.¹ Refining the models by trimming outliers and applying a variable-selection technique reduced model complexity while maintaining predictive performance, though the degree of improvement varied by dye.¹ The research team also calculated practical detection thresholds, which are the lowest adulteration levels reliably flagged with repeated measurements, of approximately 0.26% for Allura Red, 0.37% for Ponceau 4R, and 1.75% for Orange II.¹

What were the limitations of this study?

Although the researchers achieved promising results, there were still limitations with the method used. The first of these limitations is that their method was susceptible to false positives because their method detects sodium rather than the dyes themselves. As a result, LIBS cannot serve as a standalone confirmatory method, and any flagged sample would still require chromatographic or spectroscopic follow-up testing to legally confirm dye identity.¹

Using a handheld LIBS instrument is appealing because of their speed and cost. A handheld device that can screen samples on-site, without laboratory infrastructure, could allow suspect shipments to be identified faster, reducing the volume of samples requiring full chromatographic analysis and potentially shortening the time between detection and enforcement action.¹ The authors note that further work on sample preparation, including binder choice and homogenization, could improve detection limits and reproducibility ahead of broader adoption.¹

References

1. Grabska, J.; Bec, K. B.; Moll, V.; Fiegl-Lechner, A.; Huck, C. W. Quantitative Screening of Sodium Salt Azo Dyes in Paprika Powder by Handheld Laser-Induced Breakdown Spectroscopy. Analytica 2026, 7, 47. DOI: 10.3390/analytica7030047
2. Wetzel, W. New Breakthrough in Paprika Authentication: FT-NIR Analysis Ensures Quality and Detects Adulteration, Part 1. Spectroscopy Online, 2026. https://www.spectroscopyonline.com/view/new-breakthrough-in-paprika-authentication-ft-nir-analysis-ensures-quality-and-detects-adulteration-part-1 (accessed July 22, 2026).
3. Wetzel, W. New Breakthrough in Paprika Authentication: FT-NIR Analysis Ensures Quality and Detects Adulteration, Part 2. Spectroscopy Online, 2026. https://www.spectroscopyonline.com/view/new-breakthrough-in-paprika-authentication-ft-nir-analysis-ensures-quality-and-detects-adulteration-part-2 (accessed July 22, 2026).
4. Galvin-King, P.; Haughey, S. A.; Elliott, C. T. The Detection of Substitution Adulteration of Paprika with Spent Paprika by the Application of Molecular Spectroscopy Tools. Foods 2020, 9 (7), 944. DOI: 10.3390/foods9070944