# Monitoring Antioxidant Preservation in Microwave-Dried Tea Using H2O2-Responsive Electrochemical Sensor

## TL;DR

This paper introduces a new electrochemical sensor to monitor antioxidant preservation in tea during microwave drying.

## Contribution

A novel H2O2-responsive electrochemical sensor using Au/MOF(Zn) is developed for real-time antioxidant assessment in tea.

## Key findings

- The sensor detects H2O2 with a wide linear range (400 μM to 1.8 mM) and high correlation (0.9983).
- Optimal antioxidant preservation in tea occurs at 120 seconds of microwave drying.
- Higher microwave power increases antioxidant activity, while prolonged low-power drying reduces it after a peak.

## Abstract

Considering the demand for nutritional assessment and product quality control in the tea industry, this work develops an effective electrochemical sensor based on gold nanoparticles electrodeposited onto a zeolitic imidazolate framework (Au/MOF(Zn)) for evaluating the antioxidant activity of tea subjected to microwave-assisted drying (MAD) through hydrogen peroxide (H2O2) scavenging. The MOF(Zn) enables uniform deposition of AuNPs, which significantly enhances the electrocatalytic oxidation of H2O2. The fabricated sensor exhibits a wide linear detection range from 400 μM to 1.8 mM for H2O2 with a correlation coefficient of 0.9983. The experimental results demonstrate acceptable selectivity, with signal interference <5% from common tea compounds like inorganic ions, sugars, and organic acids. Electrochemical methods, including cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis, were employed to quantify H2O2 by measuring oxidation currents in phosphate-buffered saline (PBS, pH 7.0). The relative standard deviation (RSD) for repeatability and reproducibility was 5.1% and 6.8%, respectively, confirming high reliability. This sensor was successfully applied to assess antioxidant capacity in tea extracts obtained from fresh leaves subjected to microwave-assisted drying under varying power and duration. Results indicate that increasing microwave power enhances antioxidant activity, while prolonged drying at low power initially increases activity (peaking at 120 s) but reduces it upon extended exposure. Optimal antioxidant preservation was achieved at 120 s. This real-time, reliable sensing strategy offers theoretical foundations for optimizing tea processing parameters to preserve bioactive compounds, particularly polyphenols like catechins, thereby improving tea quality and health benefits.