Analysis of Phenolic Content in Grape Seeds and Skins by Means of a Bio-Electronic Tongue.

Cristina Garcia-Cabezon,Guilherme Gobbi Teixeira,Celia García-Hernandez,Maria Luz Rodriguez-Mendez,Fernando Martin-Pedrosa,Luís Guimaraes Dias,Coral Salvo-Comino

doi:10.3390/s20154176

Cristina Garcia-Cabezon, Guilherme Gobbi Teixeira + Show 5 more

Open Access

https://doi.org/10.3390/s20154176

Copy DOI

Abstract

A bio-electronic tongue has been developed to evaluate the phenolic content of grape residues (seeds and skins) in a fast and easy way with industrial use in mind. A voltammetric electronic tongue has been designed based on carbon resin electrodes modified with tyrosinase combined with electron mediators. The presence of the phenoloxydase promotes the selectivity and specificity towards phenols. The results of multivariate analysis allowed discriminating seeds and skins according to their polyphenolic content. Partial least squares (PLS) has been used to establish regression models with parameters related to phenolic content measured by spectroscopic methods i.e., total poliphenol content (TPC) and Folin–Ciocalteu (FC) indexes. It has been shown that electronic tongue can be successfully used to predict parameters of interest with high correlation coefficients (higher than 0.99 in both calibration and prediction) and low residual errors. These values can even be improved using genetic algorithms for multivalent analysis. In this way, a fast and simple tool is available for the evaluation of these values. This advantage may be due to the fact that the electrochemical signals are directly related to the phenolic content.

Highlights

In grape berries, polyphenolic compounds are mainly found in skins and seeds
Whatever the grape’s variety, seeds showed higher absorbance values than skins, confirming that seeds are the grape components that have the highest content of phenolic compounds
It is known that total extractable phenolics in grape vary between 60–70% in the seeds and 28–35% in the skin, being about

Summary

Introduction

Polyphenolic compounds are mainly found in skins and seeds. Many factors are essential in the phenolic composition of grapes, namely degree of ripeness, climate conditions, grapevine variety and berry size [1,2]. The most abundant phenolic compounds in grape skins are flavonols, while grape seeds have high levels of flavan-3-ols [2]. During wine making, these compounds are transferred to wines and have an important influence in the final organoleptic characteristics of wines. The grape marcs (seeds and skin remains of grapes after pressing) have a high content on polyphenols, increasing the interest of exploiting these sub-products [3]. Bekhit et al [4]

Objectives

Methods

Results