Contribution of SO2 to antioxidant potential of white wine
Helena Abramovicˇ, Tatjana Košmerl, Nataša Poklar Ulrih, Blazˇ Cigic´ ⇑
Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia
a r t i c l e i n f o
Article history:
Received 25 April 2014
Received in revised form 14 October 2014
Accepted 4 November 2014
Available online 11 November 2014
Keywords:
Antioxidant potential
DPPH
Folin Ciocalteu
SO2
Wine
Polyphenols
Solvent composition
Trolox equivalent
Synergistic effect
a b s t r a c t
The reactivity of SO2 with the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and in Folin Ciocalteu (FC)
assays was analysed under different experimental conditions. There was significantly higher reactivity
between SO2 and DPPH in buffered methanol than in methanol alone. When DPPH and FC assays were
performed in a mixture of caftaric acid and SO2, there were synergistic effects that were more pronounced
with the FC assay. Phenolics are an important parameter of wine quality, and their accurate
characterisation in wine is essential. Analysis of white wines with DPPH and FC assays overestimates
the contribution of phenolics to the antioxidant potential (AOP). SO2 contributes (from 20% to 45%) to
the AOP of the white wines analysed. As SO2 reactivity depends highly on buffer composition, pH, time
of incubation and other compounds, e.g. phenolics and aldehydes, different experimental protocols can
produce large variations in AOPs, and therefore control of experimental conditions is extremely
important.
2014 Published by Elsevier Ltd.
1. Introduction
Numerous studies have shown that phenolic compounds in
wine have high antioxidant potential (AOP) due to their free radical-
scavenging. As the making of red wine includes maceration and
making white does not, white wines contain lower levels of phenolic
compounds (Roussis et al., 2008) and consequently have lower
AOPs than have red wines (Oliveira, Silva Ferreira, De Freitas, &
Silva, 2011; Paixão, Perestrelo, Marques, & Câmara, 2007; Staško
et al., 2008).
The most common phenolics in white wines are non-flavonoid
compounds, such as hydroxycinnammates and benzoic acids.
Among these phenolic acids, caffeic acid and its derivative with
tartaric acid (i.e., caftaric acid) and gallic acid predominate. Catechin
is the most abundant flavonoid in white wines, and it commonly
constitutes up to 20% of the total phenolic content
(Oliveira et al., 2011; Roussis et al., 2008; Waterhouse, 2002).
The AOP of wines is largely attributable to their total phenolic content.
In general, the AOP and phenolic levels in wines are closely
related, as determined by the Folin Ciocalteu (FC) method
(Minussi et al., 2003; Paixão et al., 2007) or by HPLC analysis
(Staško et al., 2008). However, compared to red wines, in white
wines, the correlation between AOP and phenolic levels is less
pronounced (Staško et al., 2008), and so other non-phenolic components
might also contribute to the AOP.
Free radical-scavenging activities have been thoroughly studied,
and various experimental assays have been developed for their
evaluation. The 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) is a
synthetic nitrogen-centred radical, and it is one of the most frequently
used species to investigate and rank compounds and foods
according to radical-scavenging activities. The DPPH assay measures
the intrinsic ability of a compound to transfer a hydrogen
atom or an electron to the DPPH radical, which results in the formation
of DPPH2, with a parallel decrease in DPPH concentration.
However, some previous reports (Hotta et al., 2002) have shown
that the oxidation potentials of various antioxidants do not show
good correlation with the DPPH-scavenging activities. Furthermore,
it has been established that the course of the reaction
between DPPH and an antioxidant does not depend only on the
nature of the scavenger, but also on the solvent used in the assay.
Indeed, higher reactivities of antioxidants with DPPH have been
estimated in water, as compared to in methanol (Dawidowicz,
Wianowska, & Olszowy, 2012). In this respect, such antioxidant
measurements should be performed over incubation times where
the reaction between DPPH and the antioxidant reaches steadystate.
However, although DPPH is recognised as being stable, its
reduction in the absence of added antioxidant with prolonged
incubation times has also been reported (Bertalanicˇ, Košmerl,
Poklar Ulrih, & Cigic´ , 2012). Therefore, to obtain relevant data,
http://dx.doi.org/10.1016/j.foodchem.2014.11.030
0308-8146/ 2014 Published by Elsevier Ltd.
⇑ Corresponding author. Tel.: +386 1 3203784; fax: +386 1 2566296.
E-mail address: blaz.cigic@bf.uni-lj.si (B. Cigic´ ).
Food Chemistry 174 (2015) 147–153
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