Multienzyme-like MnO2@Ag aerogel as SERS/colorimetric sensing platform for the fermentation process of tea and assess the total antioxidant capacity

The unique feature of tea fermentation is the oxidation of polyphenols, which contributes to the distinct total antioxidant capacity (TAC) of different teas. In this study, we designed and synthesized a MnO2@Ag nanosheet aerogel with diverse enzyme-like activity. It exhibits an intrinsic laccase-like activity, capable of effectively oxidizing catechins to mimic the tea fermentation process, thereby generating quinone-type oxidation products (oxCC). Additionally, the MnO2@Ag aerogel exhibits surface-enhanced Raman scattering (SERS) activity, which allows for the sensitive detection of epigallocatechin gallate (EGCG) down to 1 µM. By utilizing the EGCG-induced MnO2@Ag aerogel, we have established an EGCG-TAC sensing platform to evaluate the TAC of various teas. The results indicate that the TAC of green tea > oolong tea > black tea > Pu'er tea, with Xinyang Maojian exhibiting the strongest TAC in green tea, reaching 889 µM EGCG.