Determination of Phenolic Content in Different Barley Varieties and Corresponding Malts by Liquid Chromatography-diode Array Detection-Electrospray Ionization Tandem Mass Spectrometry.

Daniel Carvalho,Andreia Curto,Luís Guido

doi:10.3390/antiox4030563

Abstract

A simple and reliable method for the simultaneous determination of nine phenolic compounds in barley and malted barley was established, using liquid chromatography-diode array detection-electrospray ionization tandem mass spectrometry (HPLC-DAD-ESI-MS/MS). The phenolic compounds can be easily detected with both systems, despite significant differences in sensitivity. Concentrations approximately 180-fold lower could be achieved by mass spectrometry analysis compared to diode array detection, especially for the flavan-3-ols (+)-catechin and (−)-epicatechin, which have poor absorptivity in the UV region. Malt samples were characterized by higher phenolic content comparing to corresponding barley varieties, revealing a significant increase of the levels of (+)-catechin and (−)-epicatechin during the malting process. Moreover, the industrial malting is responsible for modification on the phenolic profile from barley to malt, namely on the synthesis or release of sinapinic acid and epicatechin. Accordingly, the selection of the malting parameters, as well as the barley variety plays an important role when considering the quality and antioxidant stability of beer.

Highlights

Barley is an abundant source of phenolic compounds and can be consider an excellent dietary matrix of natural antioxidants for disease prevention and health promotion
Other bound phenolic acids found in barley are vanillic, sinapinic, and p-hydroxybenzoic acids [2,9,14,16,17,18].Barley grains contain a range of flavan-3-ols from monomers ((+)-catechin and (−)-epicatechin), dimers, and trimers, up to higher-molecular weight flavonoid-derived tannins [9,19,20]
The analyzed phenolic compounds can be divided into three main categories: benzoic acid derivatives, cinnamic acid derivatives and flavan-3-ols ((+)-catechin and (−)-epicatechin)

Summary

Introduction

Barley is an abundant source of phenolic compounds and can be consider an excellent dietary matrix of natural antioxidants for disease prevention and health promotion. Barley contains different classes of phenolic compounds, such as benzoic and cinnamic acid derivatives, proanthocyanidins, quinines, flavonols, chalcones, flavones, flavanones, and amino phenolic compounds. They can be found in a free, esterified or in an insoluble bound form and they are quantitatively distributed between different tissues of the grains [1,7,8,9,10,11,12,13,14,15]. Other bound phenolic acids found in barley are vanillic, sinapinic, and p-hydroxybenzoic acids [2,9,14,16,17,18].Barley grains contain a range of flavan-3-ols from monomers ((+)-catechin and (−)-epicatechin), dimers (prodelphinidin B3 and procyanidin B3), and trimers (procyanidin C2), up to higher-molecular weight flavonoid-derived tannins [9,19,20]

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Conclusion