A Novel and Reliable Analysis Method Utilizing Hennosides to Improve the Quality Assessment of Lawsonia inermis L. Material Used in Cosmetic Formulations

Lawsonia inermis L. is renowned for its hair dyeing properties, with henna quality and safety often regulated by restrictions on the lawsone (2-hydroxy-1,4-naphthoquinone) content. In henna leaves, lawsone exists as glycosylated precursors, hennosides A, B, and C. Aqueous maceration revealed the sensitivity of enzymatic lawsone release, while ethanol extraction inhibited β-glucosidase activity, enabling controlled hennoside extraction. Hennoside A was isolated via RP-column chromatography and characterized using ESI-TOF, 1H-/13C-NMR, COSY, NOESY, HSQC, and HMBC. The purified compound proved suitable as an HPLC reference standard. The acidic hydrolysis of hennoside-rich extracts highlighted the limitations of lawsone-based analysis, underscoring glycosylated precursors as more reliable quality markers. Lawsone quantification via enzymatic or acid catalysis demonstrated varying accuracy in quality control. A hennoside-based approach ensures consistency by estimating the maximum releasable lawsone without inducing its formation, providing a more robust metric for a henna quality assessment.