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1. EFFECT OF OAK WOOD CHIPS IN THE ANTHOCYANIN EXTRACTION FROM
GRAPE SKINS PREVIOUSLY CLASSIFIED USING NEAR INFRARED HYPERSPECTRAL
IMAGE
B. Baca-Bocanegra1
, J. Nogales-Bueno1, F. J. Rodríguez-Pulido1, F. J. Heredia1,
J. M. Hernández-Hierro1
1 Food Colour & Quality Laboratory, Department of Nutrition & Food Science, Universidad de Sevilla.
INTRODUCTION
Color is one of the main characteristic defining the quality of wines. Anthocyanins extracted from
grape skin are the principal compounds involved in the color of red wines and their interactions with
other phenolic compounds (called copigments), normally colorless, allow improving the color
stabilization of aged wines by copigmentation reactions [1]. The expression of the color in red wines
depends not only from the amount of anthocyanin present in the grapes, but also the amount of
them that may be extracted from grapes.
MATERIAL AND METHODS
Samples
V. vinifera L. cv. Syrah and Tempranillo red grape samples were collected
from two vineyards located in the Condado de Huelva Designation of Origin
D.O. (Andalusia, Spain). Tempranillo and Syrah grapes were collected when
the vineyards were harvested (August 12 and 27, 2013 respectively). One
hundred single berries were collected for each variety. Afterwards, samples
were refrigerated and they were immediately carried to the laboratory,
tempered and subjected to the hyperspectral analysis.
Hyperspectral analysis and sample selection
Hyperspectral imaging was used to classify the grapes according to the amount of anthocyanins
transferred to the extraction media [3]. Since extractable content of anthocyanin is lower in Syrah
grapes than Tempranillo grapes the aforesaid cultivar was considered the most interesting variety
for the assay. Syrah grapes were classified as high or low extractable anthocyanin content grapes
according to the values predicted by the hyperspectral analysis. Statistical median value (1.8 m g-1
grape skin) was used as cut-off value. Ten Syrah grapes classified as low extractable anthocyanin
grapes were used in that assay.
Determination of reference parameters
Each of the ten selected Syrah grape skins was split into two parts. Then were underwent to
simulated maceration in wine-like solution (12.5% ethanol, 4 g L-1 of tartaric acid adjusted at pH 3.6
with NaOH 0.5 M), with French oak (Quercus petraea L.) wood light toasted oak chips or without as
a control. Oak wood chips were added to the wine-like solution in a 4 g L-1 ratio. Grape skins were
added to extraction media in a 1:20 ratio. For each sample, anthocyanin composition of the extracts
was measured at the third day of maceration. In order to measure the extractable anthocyanin
content, the supernatant was diluted 1:2 with 0.1M HCl, filtered through 0.45 µm pore size filters
and directly injected into the chromatographic system. Anthocyanin chromatographic analysis was
carried out following a modification of García-Marino et al. [4] as described elsewhere in
Hernández-Hierro et al. [5]. The results were expressed as mg of malvidin-3-O-glucoside equivalents
per gram of grape skin.
RESULTS
CONCLUSIONS
Anthocyanin compounds were identified by HPLC analysis at 520 nm
and comparing their retention times and spectral characteristics with
data reported by relevant literature references. The separation carried
out by HPLC allowed the quantification of 15 anthocyanins. The sum of
all them was also expressed as total anthocyanins. The figure below
shows total extractable anthocyanin content obtained for each sample
with and without oak wood chips by HPLC analysis. The results, taking
into account only the samples without oak chips, are in accordance
with values previously predicted by the hyperspectral method; only two
samples have total extractable anthocyanin content slightly higher than
1.8 mg g-1 grape skin. These results confirm that the aforementioned
hyperspectral method present a good potential for the classification of
grapes according to extractable anthocyanin contents.
It can be assumed from the results that the presence of oak wood chips in the extraction media did not cause significant changes in the anthocyanin extractability for all samples. This practice do not promote
the extraction of anthocyanins from skin but could improve or stabilize wine color due to the formation of new and more stable pigment than anthocyanins since a higher extraction of specific colorless oak
chips-related compounds that can act as good copigments take place or could also protect anthocyanins against oxidation. So, the addition of oak wood chips may be a good technique to obtain red wines
that may present high color quality and stability due to the copigmentation procedure. Moreover hyperspectral method used here for the selection of samples presents a good potential for the classification
of grapes according to extractable total anthocyanin contents.
Principal component analysis was used as an unsupervised
pattern recognition method in order to obtain a general
overview. The figure below shows the projection of the
samples on the plane defined by the first and second
principal component. The first principal component (PC1)
describes 54.72 % of the variability in the data and the
second (PC2) describes 26.10 %. In the score plot the
samples are represented by a color code indicating the
presence or absence of oak wood chips. In this graph it is
not possible to observe a trend among extractable
anthocyanin contents from samples extracted in model
wine solution with or without oak wood chips.
A univariate analysis of variance was carried out using
extractable anthocyanin contents as dependent variables and
presence or absence of oak wood chips in the model wine
solutions as independent variable. Results are shown in the
table. No significant differences were found among wines and
for each variable after a maceration process with oak wood
chips (p>0.05).
References Acknowledgements
The Spanish MINECO is thanked for J. Nogales-Bueno FPI grant (BES-2012-060192) and project AGL2014-58486-C2. Universidad de
Sevilla is thanked for J.M. Hernández-Hierro extension of Juan de la Cierva postdoctoral contract and mobility grant (SOL2016-6743) and
also for B. Baca-Bocanegra predoctoral grant (VPPI-Universidad de Sevilla). The authors also thank the technical staff of Biology Service
[Servicios Generales de Investigación (SGI), Universidad de Sevilla].
[1] B. Gordillo, M.J. Cejudo-Bastante, F.J. Rodriguez-Pulido, M.L. Gonzalez-Miret, F.J. Heredia, Food Chem, 141, 2184-2190. (2013).
[2] P. Ribereau-Gayon, Y.Glories, A. Maujean, D. Dubourdieu, Handbook of Enology, vol. 2, the Chemistry of Wine: Stabilization and Treatments.
John Wiley & Sons Ltd., Baffins Lane, Chichester, 2000.
[3] J. Nogales-Bueno, B. Baca-Bocanegra, F. J. Rodríguez-Pulido, F. J. Heredia and J. M. Hernández-Hierro, Food Chem, 172, 559 – 564. (2015).
[4] M. García-Marino, J. M. Hernández-Hierro, J. C. Rivas-Gonzalo and M. T. Escribano-Bailón, Anal. Chim. Acta, 660, 134 – 142. (2010).
[5] J. M. Hernández-Hierro, J. Nogales-Bueno, F. J. Rodríguez-Pulido and F. J. Heredia, J. Agr. Food. Chem, 61, 9804–9809. (2013)
Grupo de Color y Calidad de Alimentos, Dpto. Nutrición y Bromatología.
Facultad de Farmacia, Universidad de Sevilla. 41012 SEVILLA (Spain) (bbaca1@us.es)
Several factors have been shown to affect the extraction of phenolic compounds into must [2]. The
main goal of this study was to evaluate the effect of the addition of oak wood chips as copigments
sources on the extractability of anthocyanin from grape skins. Grapes were previously selected
using hyperspectral imaging according to the amount of anthocyanins transferred to the extraction
media [3].
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