Role of saponins on enhancement of quality of Mahī, a traditional herbal ink of early Assam

Abstract

Assam had a unique heritage of manuscript writing using a unique traditional herbal ink called Mahī, which started by 7th century and continued till the early 20th century. Here, we explored the interactions of surfactants of various charge types as it directly influences the color, adhesion and glossiness of Mahī on Sāncipāt, a popular writing base for Mahī. The interactions of synthetic surfactants of various charge types with two major and typical polyphenols of Mahī, viz., gallic acid (GA) and quercetin (QC), and their complexes with Fe2+ have been studied by spectrophotometric methods and correlated with saponins. The critical micellar concentration of lyophilized Mahī has been found to be 1.4 mg/L. It has been observed that true equilibrium binding constants (KC) from Ketelaar's equation for the complex [GA-Fe2+] in micellar solution was decreased in the order: CTAB > TX-100 > SDS. Although the color intensification of [GA-Fe2+] and [QC-Fe2+] complexes were increased by micelles of anionic surfactant, the true equilibrium binding constant of the [GA-Fe2+] complex decreased in presence of this surfactant via electrostatic attraction between the complex and the surface of SDS micelle.