Wine astringent compounds monitored by an electrochemical biosensor.

An innovative approach for monitoring astringent polyphenols in beverages (wines) is described, consisting of an electrochemical biosensor constructed by adsorbing salivary α-amylase or proline-rich protein (PRP) onto amined gold screen-printed electrodes. Interaction with polyphenols was tested using pentagalloyl glucose (PGG) as a standard, an important representative element for astringency. The analytical properties of the resulting biosensors were evaluated by electrochemical impedance spectroscopy at different pHs. The PRP-biosensor was able to bind to PGG with higher sensitivity, displaying lower limit of the linear range of 0.6 µM. Wine samples were tested to prove the concept and the concentrations obtained ranged from 0.17 to 4.7 µM, as expressed in PGG units. The effects of side-compounds on PRP and on α-amylase binding to PGG were tested (gallic acid, catechin, ethanol, glucose, fructose and glycerol) and considered negligible. Overall, concentrations > 1.0 µM in PGG units are signaling electrochemical impedance, providing a quantitative monitoring of astringent compounds.