3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
grape skin extract of St. Laurent wine variety and Fenton’s
reagents, in the presence of DMPO spin trap. As follows from
simulation analysis, in the presence of pure water, dominantly
the formation of • OH radicals is observed, whereas in
pure methanol (reference sample), the formation of different
types of carbon-centred radicals is to be found, in accord with
our previous experiments and already published data. 14,15,18
The addition of grape skin extracts into system resulted in the
decrease of spin adduct concentration as a result of competitive
reactions between the antioxidants, generated free radicals
and spin trap. 15,18,19
Staško et al., suggested previously the expression of
antioxidant activity of Tokay wines as the relative amounts of
radicals scavenged 19 . Using this approach, we can conclude
that antioxidant properties of St. Laurent variety extract is
significantly lower than that of Alibernet (66 % and 89 %,
respectively, for extracts prepared from 1.0 g at 40 °C). As
we moreover proved, antioxidant activity of extracts is in
both cases strongly dependent on extraction temperature, falling
down to 9 % for St. Laurent extract prepared from 1.0 g
at 120 °C, whereas that of Alibernet descended practically to
zero. •DPPH and ABTS •+ radicals assays are traditionally
used for food samples radical-scavenging ability (RSA) evaluation.
They were previously successfully used, e. g., for tea
or wine samples characterisation. 15,18-20 As we confirmed,
extracts of both varieties prepared at 40 °C demonstrated significant
ability to terminate • DPPH and ABTS •+ .
Pellegrini et al. suggested the effective comparison of
RSA for different food products, based on Trolox-equivalent
antioxidant capacity (TEAC) calculation 21 . Following
this approach, TEAC value of each extract was calculated
for reactions with both • DPPH and ABTS •+ . As follows from
the results obtained, the increasing extraction temperature
TEAC ABTS•+ values of St. Laurent variety (Fig. 2.) are slightly
TEAC (mmol Trolox/dm 3 )
9.0
7.5
6.0
4.5
3.0
1.5
0.0
40 60 80 100 120
Extraction temperature, °C
0.5 g
1.0 g
1.5 g
s798
lower in comparison to that of Alibernet, only slightly influenced
by extraction temperature. On the other hand, TEA-
C DPPH • values differ significantly, in the case of St. Laurent
extracts prepared from 1.0 g, they range from 1.50 to 1.75,
whereas in the case of Alibernet from 3.7 to 4.0.
U V - V I S E x p e r i m e n t s
The TPC content of all extracts under study was monitored
and expressed as Gallic acid equivalent (GAE) 16 . The
results obtained indicate that the content of polyphenols in
Alibernet variety extracts is more than two times higher than
that of St. Laurent. This would explain generally higher antioxidant
and radical-scavenging activities of Alibernet extracts.
Significant correlation (> 85%, P > 0.01) between the
TPC and TEAC for both types of extracts was achieved, in
dependence on the mass of grape skins used for the extract
preparation. As follows from data presented in Table I, correlation
is better for St. Laurent varieties, probably due to
different composition of polyphenols.
Table I
Correlation matrices between the TPC content and radicalscavenging
abilities of grape skin extracts
St. Laurent
TPC TEAC ABTS•+ TEAC •DPPH
TPC 1 0.9778 0.9518
TEAC ABTS•+ 0.9778 1 0.9060
TEAC •DPPH 0.9518 0.9060 1
Alibernet
TPC TEAC ABTS•+ TEAC •DPPH
TPC 1 0.8650 0.9220
TEAC ABTS•+ 0.8650 1 0.6909
TEAC •DPPH 0.9220 0.6909 1
As a result of growing extraction temperature from
40 °C up to 120 °C, approx. 20% and 40% decrease of the
TPC content in extracts of St. Laurent and Alibernet varieties
was noticed, respectively.
Figure 2: Trolox equivalent antioxidant capacity (TEAC) of St. Laurent extracts, prepared at
different temperature from different mass of crude grape skins in the reaction with ABTS •+ Fig. 2. Trolox equivalent antioxidant capacity (TEAC) of
St. Laurent extracts, prepared at different temperature from
.
different mass of crude grape skins in the reaction with AbTS•+ Fig. 3. Classification – recognition of both wine grape varieties
(1–30 Figure – 3: St. Classification Laurent, 31–60 – recognition – Alibernet) of both wine based grape on varieties principal (1-30 com–
St. Laurent, 31-6
ponent Alibernet) analysis
based on principal component analysis.