Abstract
Bee pollen may be contaminated with pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs), which are mainly detected by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS), even though the use of fast near-infrared (NIR) spectroscopy is an ongoing alternative. Therefore, the main challenge of this study was to assess the feasibility of both a lab-stationary (Foss) and a portable (Polispec) NIR spectrometer in 60 dehydrated bee pollen samples. After an ANOVA-feature selection of the most informative NIR spectral data, canonical discriminant analysis (CDA) was performed to distinguish three quantitative PA/PANO classes (µg/kg): < LOQ (0.4), low; 0.4–400, moderate; > 400, high. According to the LC–MS/MS analysis, 77% of the samples were contaminated with PAs/PANOs and the sum content of the 17 target analytes was higher than 400 µg/kg in 28% of the samples. CDA was carried out on a pool of 18 (Foss) and 22 (Polispec) selected spectral variables and allowed accurate classification of samples from the low class as confirmed by the high values of Matthews correlation coefficient (≥ 0.91) for both NIR spectrometers. Leave-one-out cross-validation highlighted precise recognition of samples characterised by a high PA/PANO content with a low misclassification rate (0.02) as false negatives. The most informative wavelengths were within the < 1000, 1000–1660 and > 2400 nm regions for Foss and > 1500 nm for Polispec that could be associated with cyclic amines, and epoxide chemical structures of PAs/PANOs. In sum, both lab-stationary and portable NIR systems are reliable and fast techniques for detecting PA/PANO contamination in bee pollen.
Highlights
Bee pollen is a mixture of flower pollen, nectar and bee saliva
In 17 (37%) of the contaminated samples, the sum of pyrrolizidine alkaloids (PAs)/ PANO concentration was over the value of 400 μg/kg, which has been considered as threshold for further analyses performed in this study
The outcomes of this study indicate the potential capability of NIR spectroscopy to perform reliable screening of bee pollen samples contaminated with PAs/PANOs
Summary
Bee pollen is a mixture of flower pollen, nectar and bee saliva. This beehive product is rich in essential nutrients and biologically active substances, such as phenolic compounds that can exhibit antioxidant, anti-inflammatory and anti-microbial activity. PAs/PANOs are secondary metabolites produced by plants as a chemical defence against herbivorous insects. They are predominant in all genera of the Boraginaceae family, in the Senecioneae and Eupatorieae tribes (Asteraceae), but they are present in the genus Crotalaria (Fabaceae) [3]. The toxicity of PAs/PANOs is dependent on their chemical structure [6]. Those compounds that contain a double bond at the 1,2-position of the necine base can be transformed into highly reactive pyrroles in the liver.
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