3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P98 ANTIOxIDANT PROPERTIES OF GRAPE
SKINS ExTRACTS INVESTIGATED by EPR
AND uV-VIS SPECTROSCOPy
LEnKA ŠťAVíKOVá a and MARTIn POLOVKA b
a Department of Food Chemistry and Biotechnology, Faculty
of Chemistry, Brno University of Technology, Purkyňova 118,
612 00 Brno, Czech Republic,
b Department of Chemistry and Food Analysis, VÚP Food
Research Institute, Priemyselná 4, 824 75 Bratislava,
Slovak Republic,
stavikova@fch.vutbr.cz
Introduction
The growing attention is recently focused on the improvement
of human health by the consumption of food or food
supplements rich in antioxidants. Grape skins contain a
plenty of different flavonoids, e.g., quercetin, catechins, flavonols,
anthocyanidins, phenolic acid derivatives and other
compounds. Anthocyanins, as the most abundant of them,
are associated with the colour of several aerial and subterranean
organs in many plants. In grapevines, anthocyanins are
accumulated in leaves during senescence and are responsible
for the colouration of grape skins in red and rosé cultivars,
and in the grape pulp, respectively. These pigments are water
soluble and reveal the beneficial effects on human health,
including the enhancement of visual acuity, but evinced also
anticarcinogenic, antimutagenic or anti-inflammatory action.
The reduction of coronary heart disease and thus the phenomenon
known as the “French Paradox” is attributed to them,
as well. 1-5
Main interest is paid to the isolation of phenolic compounds
from grapes and wine. A great effort is given to choose
a suitable extraction system for anthocyanins isolation,
as they are highly reactive compounds and exceptionally
sensitive to pH changes 6,7 . Supercritical fluid extraction with
carbon dioxide and pressurized liquid extraction with acidified
water, sulphured water or acidified organic solvents were
successfully applied for the extraction of different phenolic
compounds from grapes and wines in the past. 8-11
In this contribution, the complex study of grape skin
methanolic extracts, prepared by Pressurized Fluid Extraction
(PFE) 12,13 from two wine grape varieties, St. Laurent and
Alibernet from Velké Pavlovice and Mikulov sub-regions
(South Moravia region, Czech Republic) is presented.
Experimental
Respective methanolic extracts were prepared from three
different amounts (0.5 g, 1.0 g and 1.5 g) of either crude dried
grape skins (St. Laurent) or lyophilized grape skin powders
(Alibernet) using the PFE extraction at different temperature
(40 °C–120 °C) and pressure of 15 MPa12, 13 3 6 9 12 15 18 21 24 27 30 33
3 6 9 12 15 18 21 24 27 30 33
Time after H O addition, min
2 2 Time after H O addition, min
2 2
Fig. 1. The time evolution of EPR spectra recorded in system
.
containing deionised water, methanol (reference) and methano-
Figure 1: The time evolution of EPR spectra recorded in system containing deionised water,
Antioxidant activity of extracts was tested by EPR methanol lic extracts (reference) of and St. methanolic Laurent variety extracts of prepared St. Laurent from variety 1.5 prepared g of crude from 1.5 g of
spectroscopy using the Bruker portable EPR spectrome- crudegrape grape skins at at 40 -40–120 120°C, respectively; °C, respectively; Fenton’s Fenton’s reagents and reagents DMPO spin and trap. Spectra
ter e-scan with accessories in Fenton system (H 2 O 2 /Fe 2+ ),
generating reactive hydroxyl radicals ( • OH) followed by
s797
spin trapping technique, using the 5,5-dimethylpyrroline-noxide
(DMPO) as spin trap 14 . In addition, radical scavenging
activity of extracts was assessed applying 2,2-diphenyl-1picrylhydrazyl
( • DPPH) free radical and 2,2’-azino-bis-(3ethylbenzthiazoline-6-sulfonic
acid) cation radical (ABTS •+ )
assays. All the experiments were performed at 298 K, using
the same quartz flat cell. EPR spectra were processed similarly
as previously described elsewhere 15 .
Total phenolic compounds’ content (TPC) of individual
extracts was determined using the Folin-Ciocalteu assay and
their tristimulus colour values (CIE Lab) were estimated,
using the UV-VIS spectrophotometer Specord (Carl Zeiss,
Jena, Germany) 16,17 .
In addition, pH values of all extracts were also measured
using the combined glass electrode.
All the data obtained were subsequently correlated and
discriminated, using the multivariate statistics, involving the
canonical discriminant analysis, principal component analysis,
and canonical correlation analysis, respectively.
Results
E P R E x p e r i m e n t s
Antioxidant properties of grape skin extracts were tested
in experimental systems, in which free radicals were generated
via Fenton reaction. Fig. 1. shows typical time evolution
of EPR spectra recorded in system containing respective
H 2 O Methanol
t=40°C
t=60°C
t=80°C
t=100°C t=120°C
were recorded at 298 K using magnetic field sweep, SW=8 mT.
DMPO spin trap. Spectra were recorded at 298 K using magnetic
field sweep, SW = 8 mT