Chemical and antioxidant characterisation of Karvi (Strobilanthes callosa) honey, a rare monofloral honey from the Western Ghats of India: metabolomic insights and lumichrome as a distinctive fluorescent marker

Karvi honey, produced during the rare mass flowering of Strobilanthes callosa in the Western Ghats of India, represents a unique monofloral honey with limited scientific characterisation. In this study, eleven Karvi honey samples were comprehensively investigated to elucidate their chemical and bioactive profile. 1 H NMR spectroscopy was employed to profile major and minor sugars comprising glucose, fructose, sucrose, maltose and turanose as well as other constituents such as 5-hydroxymethylfurfural (hmf), ethanol, formic acid and phenylalanine. Chloroform extraction of honey was performed to isolate non-polar compounds, and the resulting extracts analysed using NMR and fluorescence spectroscopy identified lumichrome as a prominent fluorescent bioactive metabolite along with the antimicrobial phenyllactic acid. Additionally, ultra-high performance liquid chromatography was used to identify and quantify lumichrome, gallic acid, abscisic acid, and syringic acid in Karvi honey. Evaluation of phenolic and flavonoid contents, along with antioxidant activity, to assess the functional attributes of this honey, revealed high antioxidant activity. Further, multivariate analysis of binned NMR spectra using PCA, PLS-DA, and OPLS-DA revealed a clear separation between Apis dorsata and Apis cerana samples, illustrating a possible bee-specific classification. Together, these findings provide a compositional and metabolomic characterisation of Karvi honey and scientific documentation of this rare honey.