Quantitative amino acids profile of monofloral bee pollens by microwave hydrolysis and fluorimetric high performance liquid chromatography

Bee pollen is an attractive resource in the field of alternative remedies and thanks to the content of carbohydrates, crude fibers, proteins and lipids must be considered as a supplementary food of high potential rate. In characterization of bee pollen with the aim to define its value in human nutrition, the amino acids profile is one of the most important attributes. In the present study, the determination of amino acids composition of different monofloral bee pollen samples was obtained by an approach combining microwave acidic hydrolysis (60 min at 150 °C instead of 22 h at 120 °C in conventional oven) followed by derivatization using 9-fluorenylmethylchloroformate (FMOC-Cl) and separation of amino acids derivatives using a Phenomenex Kinetex core-shell 5 μm C18 (150 x 4.6 mm i.d.) column under a ternary gradient elution. Separation of 19 amino acids was achieved in about 40 min and fluorimetric detection (λexc = 265 nm λem = 315 nm) allowed selective and sensitive quantitation with LOQ values ranging within 0.14–3.00 μg/mL. Interestingly, the present approach allowed determination of some amino acids e.g., tryptophan and trans-4-hydroxyproline that are often lost by other methods of analysis. Significant differences in the composition of the considered samples were found confirming the impact of botanical origin of the product on its nutritional value. Principal Component Analysis was applied to treat the obtained data, highlighting the importance for discrimination, of detecting low abundance amino acids. The proposed method can be used as an advantageous alternative to the existing ones for characterization of bee pollen as an important source of dietary proteins.