Tannase-catalysed gallic acid release for clean-label inhibition of green tea auto-oxidative browning

Ready-to-drink (RTD) green tea is rich in flavan-3-ols, which readily undergo auto-oxidation, causing browning. Conventional browning inhibitors can induce undesirable ingredient interactions, flavour changes, and health concerns. Here, we explored a clean-label strategy to inhibit RTD green tea browning by releasing gallic acid from naturally present galloylated compounds using the enzyme tannase (from Aspergillus ficuum). In-depth analysis of green tea by a combination of UHPLC-HRMS, NMR, and enzymatic hydrolysis led to the (tentative) identification of 75 galloylated compounds with four scaffold types. Hydrolysis of these galloylated compounds by tannase was affected by the scaffold type, scaffold stereo configuration, position of gallate attachment, and number of gallate moieties. Tannase treatment resulted in a substantial reduction in auto-oxidative browning of green tea. These results demonstrate that tannase treatment has the potential to decrease reliance on additives for maintaining the colour of RTD green tea and other phenolic-rich beverages.