thermal processing-driven tannin transformation from gambir (uncaria gambir roxb.) into sustainable natural black pigments

Catechin and tannin are the two major compounds found in gambir, both characterized by their rich phenolic hydroxyl groups. the interaction between these phenolic hydroxyl groups in gambir and ferrous ions (fe²+) from feso4 can lead to the formation of a new colored coordination complex. therefore, the presence and stability of phenolic groups during processing must be carefully considered. one of the critical steps in black pigment production is the transformation of gambir into black cube gambir, a process conducted via controlled thermal cooking at 70 °c for a defined period. this study investigates the effect of cooking duration on the ability of gambir to form colored complexes through the production of black pigments for whiteboard marker ink. a completely randomized design (crd) was employed with five cooking time treatments (0, 30, 60, 90, and 120 minutes), each repeated three times. the results showed that cooking duration significantly influenced the formation of black pigment for whiteboard marker ink. the 90-minute cooking treatment yielded the most optimal results, producing darker and more stable pigment compared to other durations. this finding is supported by functional group analysis using fourier transform infrared (ftir) spectroscopy. ftir results indicated that the highest intensity of phenolic groups was observed in treatment d (90 minutes). this research provides a foundation for the development of more environmentally friendly natural pigment-based products derived from gambir.