Autores
Chamorro Warnken, I.P. (UNIVERSITY OF READING) ; Peña Martínez, P.A. (UNIVERSIDAD DE TALCA) ; Yanez Segovia, S.G. (UNIVERSIDAD DE TALCA) ; Pino Ramos, L.L. (UNIVERSIDAD DE TALCA) ; Laurie Gleisner, V.F. (UNIVERSIDAD DE TALCA)
Resumo
Ultrasound treatments (US) may favor the extraction of phenolics during wine
production. In this study, sonication at 20 kHz, with variable amplitudes (40
and
80 %) and treatment times (10 and 20 min) were applied to red wine cv. Carmenère
in presence of oak wood cubes. Total phenols and condensed tannins of the
sonicated wines showed no significant differences compared with untreated
controls. In contrast, hydrolyzable tannins content significantly increased as a
result of the US (80% amplitude and 20 minutes). These results suggest that the
US may be a viable alternative to accelerate the extraction of hydrolyzable
tannins from wood; however, more research should be conducted to understand the
extraction dynamics and the overall chemical and sensorial changes occurring
after US.
Palavras chaves
Ultrasound; Phenolic extraction; Oak wood
Introdução
One of the most decisive practices in determining wine quality is the maturation
typically carried out in oak barrels. This process is widely used in high-end
wines but has several disadvantages regarding its cost, duration, and
sustainability.
In the last decades, new wine aging techniques have been developed, including
the
use of wood fragments, micro-oxygenation, and the use of physical methods to
expedite phenolic extraction and aging (Tao et al., 2014). Among the
technologies
to favor the extraction of phenolic compounds from solid materials, the use of
different forms of maceration, extraction assisted by microwaves, and ultrasound
have been tested.
Ultrasound is a non-thermal processing method that has recently been approved in
winemaking. Some of the potential advantages of this technique include high
extraction efficiency, easy handling, low cost, and low environmental pollution
(Tao et al., 2014). Some authors suggest that during ultrasound treatments,
certain critical variables, such as temperature and exposure time should be
optimized in order to reduce the degradation of phenolic compounds of interest
(Zhang et al., 2015).
In this study, the effect of ultrasound treatments on the composition of
phenolic
compounds in Carmenère wine, in contact with oak wood fragments, was evaluated,
using different wave amplitudes and exposure times.
Material e métodos
Materials
Carmenère wine was made according to commercial protocols, using grapes from an
experimental vineyard located in the O'Higgins region, of Chile (34°20'06.9"S
70°47'54.3"W). Once finished, thw wine was stored in 300 mL bottles in a cold
room at 0ºC.
The Oak wood (Quercus Alba L.) treatments were carried out with medium-toasted,
Ambrosia Flavor Boost, from Tonelería Nacional (Santiago, Chile), adding 100g of
cubes (10x10x20 mm) to 250 mL of wine.
Methods
US were carried out with a SONICS, VCX-750 processor, coupled to a solid probe
306b (Washington, USA), with 750-Watt power and a frequency of 20 kHz. Wave
amplitudes were set at 40% and 80% and exposure times, at 10 and 20 minutes. In
order to isolate the effect of temperature increase from that of the ultrasound
itself, a treatment evaluating the effect of temperature on wine phenolics was
also included.
The phenolic composition of wine samples was evaluated as follows: Total
phenolics were determined by Folin-Ciocalteu assay in small volumes (Waterhouse,
A. L. 2002). Condensed tannins were determined by the methylcellulose
precipitation methodology proposed by Mercurio & Smith (2006). Hydrolyzable
tannins were determined by the quantification of the ellagic acid released from
the acid hydrolysis of tannins according to Isaza et al. (2007).
Statistical Analysis
Statistics were performed by R (version 3.4.0. 2017), comparing treatments with
one-way ANOVA, and factorial analysis between wave amplitude and exposition
time.
P<0.05 confidence interval was used. The multiple comparisons of treatments were
evaluated with a post-hoc Tukey test.
Resultado e discussão
Total phenolics
The duration of the ultrasound treatment affected total phenolic extraction. The
longest time of ultrasound resulted in wine samples with 1329.5 mg GAE/L (80%
amplitude) and 1312.9 mg GAE/L (40% amplitude), whilst 1215.0 mg GAE/L (40%
amplitude) and 1237.9 mg GAE/L (80% amplitude) was recorded when the shortest US
was applied. However, when different temperature treatments were tested, no
differences in wine phenolic concentration were observed.
These results agree with the studies of Lukić et al., (2019), Garcia et al.,
(2016), Tao et al., (2014) in which no clear trend in total phenols variation
was
reported.
Condensed tannins
Non factor (time or amplitude) had a significant effect on condensed tannins,
all
treatments reached 347.5 - 354.9 mg CE/L. This contrasts with the findings of
Lukić et al., (2019), who argued that time is a determining factor for condensed
tannins concentration. However, the frequencies were higher than those in this
study. Ferraretto & Celotti, (2016), concluded that condensed tannins were not
altered at a frequency of 20 kHz was employed.
When the temperature simulation reached 24°C it did not show any effect on
condensed tannins. However, when the temperature reached 30°C, an increase in
condensed tannins was observed.
Hydrolyzable tannins
The highest extraction of hydrolyzable tannins was obtained in the treatment
with
the highest intensity of amplitude and time, with 172.2 mg EAE/L. This is
consistent with the results of Lukić et al. (2019) and Ferraretto & Celotti
(2016) who stated that the ultrasound amplitude and time favorably influence the
extraction of these compounds.
Conclusões
Although ultrasound at 80% wave amplitude allowed a greater extraction of
hydrolyzable tannins from wood, no differences were in the total phenols and
condensed tannins. Therefore, the lower ultrasound treatment (40% wave amplitude)
and 10 min. exposure, do not allow higher extraction than obtained after
increasing the temperature of wine by other physical means.
Chemical dynamics after ultrasound treatment to wine remains a question,
regarding the nature of reactions, and selectivity of the affected compounds, to
use ultrasound as an alternative technique to conventional aging in oak barrels.
Agradecimentos
We thank Viña Santa Carolina for the cooperation with grape samples for this
research. To FONDECYT 1190301 project for financial support. We thank the team of
the Oenological Chemistry Laboratory of the Universidad de Talca.
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