Nitrogen compounds in Phacelia tanacetifolia Benth. honey: First time report on occurrence of (−)-5-epi-lithospermoside, uridine, adenine and xanthine in honey

Lacy phacelia (Phacelia tanacetifolia Borkh.) honey composition was screened by UHPLC-DAD-QqTOF-MS. The targeted analysis revealed 6 major nitrogen compounds including aromatic amino acids (tyrosine, phenylalanine), purine derivatives (adenine, xanthine), nucleoside (uridine) and rare non-cyanogenic cyanoglucoside, (−)-5-epi-lithospermoside ((2Z)-2-[(4R,5R,6S)-4,5-dihydroxy-6-(β-d-glucopyranosyl)oxycyclohex-2-en-1-ylidene]acetonitrile). Their identity was confirmed by different analytical tools: HRMS, co-chromatography with standard compound or comprehensive NMR experiments. All the compounds, except amino acids, were reported and determined in honey for the first time. The amount of the compounds was quantified in 16 unifloral phacelia samples: adenine (18.45 ± 4.63 mg/kg), xanthine (10.53 ± 2.98 mg/kg), uridine (42.84 ± 9.26 mg/kg), tyrosine (14.66 ± 10.22 mg/kg), (−)-5-epi-lithospermoside (70.61 ± 31.37 mg/kg) and phenylalanine (20.41 ± 11.99 mg/kg). The (−)-5-epi-lithospermoside content is significantly correlated with P. tanacetifolia pollen percentage (R2 = 0.5612, p < 0.001) and it is proposed as a potential marker of botanical origin for phacelia honey.