<![CDATA[This study explores the extraction of natural blue indigo pigment from Strobilanthes cusia leaves using a sequential process of anaerobic maceration and sodium hydroxide (NaOH) alkalization. Serving as a cleaner alternative to traditional quicklime (CaO) treatment, which deposits undesirable mineral residues on textiles, this method optimizes both extraction purity and pigment formulation. Fresh leaves were macerated anaerobically for three days to hydrolyze indican into indoxyl, followed by aeration and NaOH alkalization (pH 12) to facilitate oxidative coupling. The structural transformation was monitored via UV-Visible spectrophotometry, revealing a distinct shift from the precursor absorption (λmax) 291.94 nm to the indigo chromophore (λmax) 670.58 nm. Furthermore, Fourier Transform Infrared (FTIR) spectroscopy validated the indigotin molecular framework and confirmed that the NaOH-based route successfully circumvents the heavy calcium carbonate co-precipitation associated with conventional CaO extraction. To enhance physical handling, the purified extract was stabilized into a workable paste using maltodextrin. Colorimetric evaluations demonstrated that incorporating 5%, 10%, 15%, 20%, and 25% (w/v) maltodextrin provided optimal steric stabilization without impeding dye mass transfer into the cellulosic fibers, yielding excellent cycle-to-cycle dyeing reproducibility with total color differences (E*) maintained within the acceptable industrial tolerance ( 3). Ultimately, this sequential NaOH-maltodextrin approach provides a sustainable, residue-free, and highly efficient pathway for producing industry-ready natural indigo colorants.]]>
