Effect of Water Bath Heating on Tannin Content and Quality Improvement Potential of Gambier (Uncaria gambir Roxb.)

Gambir (Uncaria gambir Roxb.) is a source of natural phenolic compounds rich in catechins and tannins and has potential as a sustainable industrial raw material. During heating, phenolic compounds may undergo structural changes, including possible oxidation and polymerization, which can affect gambier quality beyond its catechin content. This study evaluated the effect of indirect heating duration using a water bath on the measured tannin content and phenolic characteristics of gambier. Four heating durations were evaluated: 0, 120, 240, and 360 minutes. The samples were analyzed for color, tannin content, total phenolic content, and functional groups using Fourier Transform Infrared (FTIR) spectroscopy. Data were analyzed using Analysis of Variance (ANOVA) at the 5% significance level. Heating duration significantly affected the characteristics of gambier. Increasing the heating duration resulted in darker and redder gambier powder, accompanied by changes in measured tannin and total phenolic contents. Tannin content increased from 23.89% in the control to 35.89% after 240 minutes of heating, then decreased to 28.17% after 360 minutes. Total phenolic content showed a similar pattern, reaching the highest value of 255.21 mg GAE/g after 240 minutes. FTIR analysis showed the presence of major phenolic functional groups, including O–H, aromatic C=C, C–O, and C–O–C, which remained detectable after heating. Based on the measured parameters, indirect heating using a water bath for 240 minutes was the most effective condition for obtaining the highest measured tannin content while maintaining the characteristic phenolic functional groups of gambier. The findings provide a basis for further development and standardization of gambier as a tannin-rich raw material for potential green industrial applications.