Paper-Based Device for Phenolic Content Determination in Tea Extracts

Introduction: Phenolic compounds garner interest in developing medicines, nutraceuticals, and cosmeceuticals based on natural products. The quantity of phenolic compounds in a sample is commonly determined via spectrophotometry; however, this instrumented technique is relatively laborious and time consuming and requires a large amount of reagents.

Objective: This work aimed to develop a simple, point-of-need colorimetric sensor to rapidly determine total phenolic content (TPC) in tea extracts.

Methodology: We developed a radial paper-based analytical device (PAD) for TPC determination based on the established colorimetric reaction between the Folin-Ciocâlteu reagent and phenols. The PAD was designed to enable quantitative (with image capturing device and color processing software) and semiquantitative (using a color palette reference card) determinations. Analytical performance and stability of the PAD were evaluated based on the color responses.

Results: The PAD was successfully applied for the determination of phenolics in tea extracts obtained using several polar protic solvents, including water, methanol, and ethanol, with satisfactory accuracy (recovery of 95.5%-104%, 110%-116%, and 104%-110%, respectively) and precision (RSD < 9%). The obtained TPC values also agreed with those from visible spectrophotometry. Semiquantitative determination using the color reference card with three categories of TPC level (i.e., 0-100, 100-500, and 500-1000 mg gallic acid equivalent/L) provided > 95% accuracy. The devices were the most stable when stored at 4°C in a light-protected, vacuum-sealed container. The proposed PAD is promising for simple, rapid (~10-20 min), and accurate estimation of TPC in plant extracts.