Contribution of phenolic acids isolated from green and roasted boiled-type coffee brews to total coffee antioxidant capacity

Paweł Górnaś,Jolanta Tomaszewska-Gras,Michał Michalak,Krzysztof Polewski,Krzysztof Dwiecki,Aleksander Siger

doi:10.1007/s00217-015-2572-1

Abstract

The antioxidant capacity (AC) of boiled-type coffee brews (CB) and phenolic acids (PA) isolated from them, obtained from the caffeinated and decaffeinated beans of different geographical origins and species and with different roasting degrees, was examined. The AC of PA and CB samples was tested in five antioxidant assays: a total antioxidants reducing capacity assay using a Folin–Ciocalteu reagent (FCR), a ferric ion reducing antioxidant power (FRAP) assay, a DPPH· radical-scavenging activity (DPPH) assay, a metal chelating activity (MCA) assay and a total radical trapping antioxidant parameter (TRAP) assay. In most samples, the total amount of phenolic acids, determined by HPLC, decreased with the increasing degree of roasting the coffee beans, leading to reduced AC. All used methods showed that CB exhibits higher AC compared with the PA samples. Phenolic acids isolated from CB samples have the main contribution (on average over 95 and 84 % in green and roasted coffee extracts, respectively) in AC of the CB samples in FCR, FRAP and TRAP assays, whereas in DPPH and MCA tests, the phenolic acid contribution in AC of CB samples was below 50 % (on average over 36 and 45 % in green and roasted coffee extracts, respectively). Significant differences between the AC values determined for CB and PA samples were noticed only for the MCA and DPPH methods which reflect the different molecular mechanisms underlying each of the assays. Additionally, the statistical methods, including principal component analysis, applied to results of antioxidant capacity obtained with different analytical techniques confirmed their feasibility to distinguish between coffee brews with different degrees of roasting, regardless of coffee origin.

Highlights

The coffee brew is one of the most frequently consumed beverages in the world, and coffee beans belong to the top trade products with global production of 8.8 million tons in 2012 [1]
The relation obtained from Principal component analysis (PCA) between methods are very similar to the results presented in correlation matrix, Table 2, where correlations coefficients were calculated separately for one type of samples, i.e., coffee brew or extracted phenolic acids
The presented study showed that the boiled-type coffee brews (CB) possesses higher antioxidant capacity (AC) compared with the extracts of phenolic acids (PA) isolated from corresponding CB samples

Summary

Introduction

The coffee brew is one of the most frequently consumed beverages in the world, and coffee beans belong to the top trade products with global production of 8.8 million tons in 2012 [1]. It is not surprising that coffee brews in some countries provide the highest amount of antioxidants in the daily diet [4, 5]. The AC of coffee brews is generally associated with the presence of phenolic compounds, primarily in the form of chlorogenic acids [6]. The profile of the components with potential AC in coffee brews is significantly affected by the degree of roasting, which depends on the parameters of the roasting process [13]. The coffee brews can be considered as a non-standardized mixture of bioactive compounds, due to the influence of many factors on final composition, with the potential AC. Presence in the system of two or more antioxidants with the different physical nature, for instance hydrophobic and hydrophilic, may contribute to occur one of the two opposite phenomena; synergism or antagonism of antioxidants [15]

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