Multispectral Authentication of Paprika Spices: Quantitative Detection of Azo Dyes by NIR and Vis–NIR Spectroscopy

Food fraud and adulteration of herbs and spices continue to be major concerns in analytical research. Paprika (Capsicum annuum L.) is particularly vulnerable to falsification due to the high market value of premium products from protected designations of origin. Adulteration commonly involves the addition of red dyes or natural colorants to disguise inferior quality and enhance the visual appearance of shelf-life. Among these, azo dyes represent the most frequently detected red colorants in adulterated paprika.
To date, limited research has explored the application of near-infrared (NIR) and visible–near-infrared (Vis–NIR) spectroscopy for addressing this issue. The latter technique, in particular, show strong potential for paprika authentication, as the visible spectral region is highly sensitive to the presence of colored additives. Despite this, most spice authentication studies remain confined to conventional analytical methods.
This study aims to establish a multispectral quantitative approach for the authentication of paprika powder. Spectral analyses were conducted using a full-range handheld Vis–NIR spectrometer (350–2,500 nm), a high-performance benchtop FT–NIR spectrometer (1,000–2,500 nm). Three azo dyes were investigated: two approved food colorants—Allura Red (E129) and Ponceau 4R (E123)—and one non-food, potentially carcinogenic dye, Orange II. Seventeen concentration levels (0.1–6%) were prepared and divided into calibration and independent test sets for regression modeling.
Results revealed that both FT–NIR and Vis–NIR spectroscopy provided highly accurate models for paprika authentication, achieving RMSEP values between 0.2–0.3% and R² values of 0.96–0.99. Remarkably, the handheld Vis–NIR spectrometer outperformed the benchtop FT–NIR in terms of model interpretability, yielding similarly strong regression performance with more easily interpretable PLSR models.

This research was supported by the Austrian Science Fund (FWF) [V1014-NBL].