Optimized Extraction by Response Surface Methodology Used for the Characterization and Quantification of Phenolic Compounds in Whole Red Grapes (Vitis vinifera).

Lisard Iglesias-Carres,Miquel Mulero,Begoña Muguerza,Lucía Sancho-Pardo,Anna Mas-Capdevila,Francisca Isabel Bravo,Anna Arola-Arnal

doi:10.3390/nu10121931

Abstract

Scientific research has focused on the characterization of bioactive polyphenols from grape seeds and skins, and the pulp has often been overlooked. However, since the beneficial properties of grapes are associated with the consumption of whole fruit, a full extraction and posterior characterization of the phenolic compounds in whole grapes is required to identify the involved bioactive compounds. Such methodologies are not currently available for the whole edible parts of red grapes. This study aimed to determine the best polyphenol extraction conditions of whole red grapes, and apply the method to characterize and quantify the polyphenol composition of three different grapes. The optimized conditions were 80 mL/g, 65% methanol (1% formic acid), 72 °C, and 100 min under agitation of 500 rpm. Also, methanol and ethanol were compared as extraction solvents, and methanol achieved statistically higher extraction rates for anthocyanins. The results of this work suggest a higher quantification of phenolic compounds when red grapes are analyzed whole, including the seeds, pulp, and skin.

Highlights

Polyphenols are plant secondary metabolites that are found in high concentrations in a wide variety of foods
The individual responses of anthocyanins, flavanols, flavonols, and hydroxycinnamic acids (HCA) were demonstrated to depend on the extraction variables, whereas no Rvt, chlorogenic acid (Chl), and p-coumaric acid (pCou) were detected in any of the extractions
This study suggests that the extraction of phenolic compounds from whole red grapes provides a higher extraction of phenolic compounds, and this is essential to be able to correlate the health effects associated with the consumption of grapes and the phenolic compounds that are responsible for these effects

Summary

Introduction

Polyphenols are plant secondary metabolites that are found in high concentrations in a wide variety of foods. More than 8000 phenol structures have been described, and several are found only in a limited number of species. Due to their beneficial health properties [1], polyphenols have attracted a large amount of interest in recent years. Grapes are one of the fruits with the highest polyphenol content, and have been investigated by many authors [2,3,4,5]. Phenolic compounds are differentially distributed in the skins, pulp, and seeds of grapes [6]. The beneficial health effects of these compounds have been reported from the consumption of phenolic compounds from whole grapes [7], grape juice [8,9], and grape seeds [10]

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