Abstract
OBJECTIVE: Improvement of application, performance, colour predictability and stability of plant-based hair colourants derived from Lawsonia inermis L. by investigating the release mechanism of lawsone during extraction and optimizing processing conditions to prevent its premature formation. A two-component system was developed, consisting of naturally occurring lawsone precursors (hennosides) in one formulation and a catalytic agent (β-glucosidase) in another. METHODS: Henna raw material was extracted using maceration, Soxhlet, and industrial-scale methods with various solvents. Extracts were analysed for yield and content of lawsone, hennosides, polyphenols, metals and reducing sugars. HPLC quantified lawsone and hennosides; reducing sugars and polyphenols were measured using dinitrosalicylic acid and Folin-Ciocalteu assays, respectively. Yak hair was dyed with different formulations and evaluated for colour outcome and wash fastness using the CIELab colour system. RESULTS: Formulations containing pre-released lawsone were unstable and ineffective after 4 weeks. In contrast, gel formulations containing hennosides without β-glucosidase remained stable for over 8 weeks and produced consistent colour when combined with the enzyme before application. Ethanolic extraction effectively yielded hennoside-rich extracts without lawsone formation. Aqueous extraction at boiling point also produced hennoside-rich extracts. Soxhlet extraction resulted in β-glucosidase activity remaining in the starting material. The two-component gel formulation demonstrated comparable wash fastness and colour intensity to the conventional paste, with improved ease and speed of application and rinsing. CONCLUSION: Optimizing henna extract processing and formulation design enabled the development of a more user-friendly, effective and stable plant-based hair dye, supporting broader consumer adoption.