3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology<br />
P98 ANTIOxIDANT PROPERTIES OF GRAPE<br />
SKINS ExTRACTS INVESTIGATED by EPR<br />
AND uV-VIS SPECTROSCOPy<br />
LEnKA ŠťAVíKOVá a and MARTIn POLOVKA b<br />
a Department of Food Chemistry and Biotechnology, Faculty<br />
of Chemistry, Brno University of Technology, Purkyňova 118,<br />
612 00 Brno, Czech Republic,<br />
b Department of Chemistry and Food Analysis, VÚP Food<br />
Research Institute, Priemyselná 4, 824 75 Bratislava,<br />
Slovak Republic,<br />
stavikova@fch.vutbr.cz<br />
Introduction<br />
The growing attention is recently focused on the improvement<br />
of human health by the consumption of food or food<br />
supplements rich in antioxidants. Grape skins contain a<br />
plenty of different flavonoids, e.g., quercetin, catechins, flavonols,<br />
anthocyanidins, phenolic acid derivatives and other<br />
compounds. Anthocyanins, as the most abundant of them,<br />
are associated with the colour of several aerial and subterranean<br />
organs in many plants. In grapevines, anthocyanins are<br />
accumulated in leaves during senescence and are responsible<br />
for the colouration of grape skins in red and rosé cultivars,<br />
and in the grape pulp, respectively. These pigments are water<br />
soluble and reveal the beneficial effects on human health,<br />
including the enhancement of visual acuity, but evinced also<br />
anticarcinogenic, antimutagenic or anti-inflammatory action.<br />
The reduction of coronary heart disease and thus the phenomenon<br />
known as the “French Paradox” is attributed to them,<br />
as well. 1-5<br />
Main interest is paid to the isolation of phenolic compounds<br />
from grapes and wine. A great effort is given to choose<br />
a suitable extraction system for anthocyanins isolation,<br />
as they are highly reactive compounds and exceptionally<br />
sensitive to pH changes 6,7 . Supercritical fluid extraction with<br />
carbon dioxide and pressurized liquid extraction with acidified<br />
water, sulphured water or acidified organic solvents were<br />
successfully applied for the extraction of different phenolic<br />
compounds from grapes and wines in the past. 8-11<br />
In this contribution, the complex study of grape skin<br />
methanolic extracts, prepared by Pressurized Fluid Extraction<br />
(PFE) 12,13 from two wine grape varieties, St. Laurent and<br />
Alibernet from Velké Pavlovice and Mikulov sub-regions<br />
(South Moravia region, Czech Republic) is presented.<br />
Experimental<br />
Respective methanolic extracts were prepared from three<br />
different amounts (0.5 g, 1.0 g and 1.5 g) of either crude dried<br />
grape skins (St. Laurent) or lyophilized grape skin powders<br />
(Alibernet) using the PFE extraction at different temperature<br />
(40 °C–120 °C) and pressure of 15 MPa12, 13 3 6 9 12 15 18 21 24 27 30 33<br />
3 6 9 12 15 18 21 24 27 30 33<br />
Time after H O addition, min<br />
2 2 Time after H O addition, min<br />
2 2<br />
Fig. 1. The time evolution of EPR spectra recorded in system<br />
.<br />
containing deionised water, methanol (reference) and methano-<br />
Figure 1: The time evolution of EPR spectra recorded in system containing deionised water,<br />
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<br />
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<br />
ter e-scan with accessories in Fenton system (H 2 O 2 /Fe 2+ ),<br />
generating reactive hydroxyl radicals ( • OH) followed by<br />
s797<br />
spin trapping technique, using the 5,5-dimethylpyrroline-noxide<br />
(DMPO) as spin trap 14 . In addition, radical scavenging<br />
activity of extracts was assessed applying 2,2-diphenyl-1picrylhydrazyl<br />
( • DPPH) free radical and 2,2’-azino-bis-(3ethylbenzthiazoline-6-sulfonic<br />
acid) cation radical (ABTS •+ )<br />
assays. All the experiments were performed at 298 K, using<br />
the same quartz flat cell. EPR spectra were processed similarly<br />
as previously described elsewhere 15 .<br />
Total phenolic compounds’ content (TPC) of individual<br />
extracts was determined using the Folin-Ciocalteu assay and<br />
their tristimulus colour values (CIE Lab) were estimated,<br />
using the UV-VIS spectrophotometer Specord (Carl Zeiss,<br />
Jena, Germany) 16,17 .<br />
In addition, pH values of all extracts were also measured<br />
using the combined glass electrode.<br />
All the data obtained were subsequently correlated and<br />
discriminated, using the multivariate statistics, involving the<br />
canonical discriminant analysis, principal component analysis,<br />
and canonical correlation analysis, respectively.<br />
Results<br />
E P R E x p e r i m e n t s<br />
Antioxidant properties of grape skin extracts were tested<br />
in experimental systems, in which free radicals were generated<br />
via Fenton reaction. Fig. 1. shows typical time evolution<br />
of EPR spectra recorded in system containing respective<br />
H 2 O Methanol<br />
t=40°C<br />
t=60°C<br />
t=80°C<br />
t=100°C t=120°C<br />
were recorded at 298 K using magnetic field sweep, SW=8 mT.<br />
DMPO spin trap. Spectra were recorded at 298 K using magnetic<br />
field sweep, SW = 8 mT