Facile thermal and hydrolytic conversion of tannic acid: Enhancement of antimicrobial activity and biocompatibility for biomedical applications

Tannic acid (TA) is a polyphenolic hydrolyzable tannin having several biological properties. However, the application of TA is limited to its performance, rendering it essential to modify TA to increase its practical applications. This study reports the facile modification of TA by thermal and hydrolysis treatments. The structures of thermally treated TA (TTA) and hydrolyzed TA (HTA) were determined by Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy (¹H NMR). Additionally, the antimicrobial, antioxidant, and cytotoxicity properties of TA, TTA, and HTA were analyzed and compared. The results confirmed the partial conversion of TTA and complete conversion of HTA into gallic acid and pyrogallol, respectively. TTA and HTA showed improved antimicrobial activity, potent antioxidant activity, and lower cytotoxicity than TA. However, HTA hydrolyzed at 200 °C exhibited the highest antimicrobial activity because of the high surface area and cell interaction. Compared to TA and TTA, HTA demonstrated a better antioxidant activity and lower cytotoxicity owing to the steric hindrance and lesser interaction between human cells and pyrogallol, respectively. Thus, HTA with potent functional properties can be prepared by a facile processing method and employed as an additive for cosmetic, packaging, and biomedical applications.