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3. Results and discussion
3.1 Effect of PEF treatments on volatile composition of Graciano, Tempranillo, and Grenache samples
Pulsed Electric Fields as a Green Pretreatment to Enhance Mass Transfer from Grapes…
DOI: http://dx.doi.org/10.5772/intechopen.104609
Results were expressed as means ± standard deviation. A p-value ≤ 0.05 was consid- ered significant (Tukey test). In figures all parameters are listed with their standard deviation. In figures for each grape variety, different letters indicate significant differences. Discriminant analyses were done with the volatile compounds areas and stilbenes and amino acids concentration in the different samples.
that monoterpenoids present in the pomace of Grenache were extracted more easily by applying PEF than those present in Tempranillo and Graciano skin because, in this work, PEF application was made in the presence of skin. Other authors have reported that phenolic compounds extraction from grape varieties depends on the morphology
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Figure 1.
Monoterpenoids average area in control and PEF treatments 1–4 in Graciano (Gr), Tempranillo (T), and Grenache (G) grape varieties (From Garde-Cerdán et al. [5]).
Pulsed Electric Fields as a Green Pretreatment to Enhance Mass Transfer from Grapes…
DOI: http://dx.doi.org/10.5772/intechopen.104609
and skin composition [37]. Probably, for this reason, a significant increase in monoter- penoids in presence of skin was found in Grenache after PEF treatments. In this regard, Delsart et al. [38] studied two PEF treatments (4 kV/cm; 1 ms and 0.7 kV/cm; 200 ms) on Cabernet Sauvignon grapes. The first PEF treatment, had an impact mainly on
vacuolar tannins, whereas the second PEF treatment had a greater impact on the parietal tannins and the skin cell walls. This enhanced polyphenol extraction kinetics. That means the degree of compound extraction from the skin is not only influenced by the grape variety but also by the type of pulse applied.
3.1.2 C13 norisoprenoids
Figure 2 shows the results of C13 norisoprenoids in the control and the samples after each of the four treatments by PEF for the three grape varieties [5]. In the case of Graciano, the total C13 norisoprenoids and (E)-β-damascenone decreased with the low- est energy treatment (Treat1). However, their presence was maintained after treating the samples at higher energy (Treat2–4). The presence of methyl jasmonate decreased by PEF application, except with Treat3 (Figure 2f). The (Z)-β-damascenone,
β-ionone, and β-cyclocitral contents were not affected by any of the treatments applied to Graciano. For Tempranillo, PEF technology was detrimental to the total content of C13 norisoprenoids, and the two isomers of β-damascenone (Figures 2a–c). The PEF treatments also decreased the presence of β-ionone upon Treat1 and 4 (Figure 2d) but they did not influence the β-cyclocitral and methyl jasmonate amount. For Grenache, only β-ionone and β-cyclocitral were affected by PEF treatments. In general, PEF favored their presence in the musts with the exception of Treat2 and 4 for the β-ionone and Treat2 for the β-cyclocitral (Figure 2d–e). These results are in agreement with those obtained by Maza et al. [32], which observed that the concentration of β-ionone, associated with the floral aroma of “violets”, which had gone undetected in the control wines, was indeed observed at concentrations greatly exceeding the odor threshold in the wines obtained from Grenache grapes treated by PEF.
Treat1 decreased the presence of total C13 norisoprenoids in Graciano by 28%, whereas, in the case of Tempranillo, all the treatments reduced the presence of these compounds by around 37%. However, in Grenache, there was no effect. C13
norisoprenoids are distributed in both pulp and skin, unlike monoterpenoids, which are predominantly present in the skin and it could be the cause that no increase was observed with PEF treatments.
In contrast to these results, Comuzzo et al. [11] observed that PEF processing of white grapes (cv. Garganega) after crushing, significantly increased the concentration of norisoprenoid glycosides in the juice of this white grape variety. In control samples, the total concentration of C13 norisoprenoids in Graciano, Tempranillo, and Grenache respectively was 7.3%, 2.0%, and 3.2%. The two compounds most abundant in all varieties were β-damascenone (both isomers) and β-ionone. β-Damascenone sum was 97% in Graciano, 92% in Tempranillo, and 98% in Grenache, while the proportion of β-ionone was 1.9% in Graciano, 5.2% in Tempranillo, and 1.3% in Grenache. These proportions varied little upon PEF treatments.
PEF effect was not selective for norisoprenoids. β-Damascenone and β-ionone.
3.1.3 Benzenoid compounds
Figure 3 shows the results for benzenoid compounds in the control and in the samples after each of the four treatments by PEF for the three grape varieties [5].
Benzenoid compounds, particularly, 2-phenylethanol and eugenol, confer a desirable aroma to the wine, with rose and clove aroma descriptors [17, 39, 40].
In the case of Graciano, treatments had neither effect on total benzenoids nor benzyl alcohol. The content of 2-phenylethanol increased with Treat1, while eugenol was only detected in this grape variety, showing that Treat4 favored its presence. For the Tempranillo variety, Treat1 and 4 resulted in a decrease in the presence of total benzenoids and 2-phenylethanol. On the other hand, benzyl alcohol was found in higher amounts in grapes treated with Treat2. For Grenache, PEF favored the pres- ence of total benzenoids and 2-phenylethanol regardless of the treatment, and Treat1 increased the presence of benzyl alcohol with respect to the control samples. By con- trast, Comuzzo et al. [33] observed a slightly decreased of 2-phenylethanol in white wines obtained by PEF processing, but this appears to have a notably low potential impact on sensory perception. By comparing the content of total benzenoids, no loss nor gain was observed upon Graciano samples treated by PEF treatments.
However, in Tempranillo, Treat1 and 4 decreased the presence of these compounds by 24%. For Grenache, all treatments, except Treat2, increased their presence by 45%.
The extraction of benzenoid compounds was increased in Grenache by PEF treatments.
Figure 2.
C13 norisoprenoids average area in control and PEF treatments 1–4 in Graciano (Gr), Tempranillo (T), and Grenache (G) grape varieties (From Garde-Cerdán et al. [5]).
Pulsed Electric Fields as a Green Pretreatment to Enhance Mass Transfer from Grapes…
DOI: http://dx.doi.org/10.5772/intechopen.104609
3.1.4 Esters
The results of esters in the control and the samples after each of the four treatments by PEF for the three varieties are shown in Figure 4. In the case of Graciano, only Treat1 favored the presence of total esters and hexyl acetate. The four PEF treatments resulted in a decrease in 2-hexen-1-ol acetate; and the presence of methyl salicylate was enhanced by Treat2 and 4. For Tempranillo, the treatments applied had no effect on the presence of esters, except for total esters and hexyl acetate in Treat3, which favored its presence; and methyl hexanoate in Treat1-3. For the latter compound, Treat1 decreased its amount, while Treat2 and 3 increased its content in the musts. On the other hand, the presence of total esters for Grenache grape variety was favored by Treat2-4. Moreover, all treatments favored the presence of methyl hexanoate, and an increase for methyl salicylate in the samples was obtained with Treat3 and 4. Maza et al. [32] obtained different results since they did not observe an increment in the concentration of total esters in wines of the Grenache grape variety by application of a PEF treatment. Esters are mainly formed during alcoholic fermentation and play an important role in wine aroma [41]. In control samples, the proportion of total esters with regard to the total amount of volatile compounds was 0.9% in Graciano, 1.1% in Tempranillo, and 0.4% in Grenache. By comparing the contents of these compounds, it can be observed that the application in the Graciano grape variety of Treat1 increased the content of esters by approximately 62%, while Treat3 resulted in a decrease of 23%.
In Tempranillo, the application of Treat3 resulted in an increase of these compounds by 29%. Finally, Treat2-4 improved its presence in Grenache by about 32%. Differences depending on grape variety were also found in the study of Fauster et al. [42], where the effects of a PEF treatment on white wine mash were significantly higher for the wines obtained from Traminer variety than those from Grüner Veltliner.
Figure 3.
Benzenoid compounds average area in control and PEF treatments 1–4 in Graciano (Gr), Tempranillo (T), and Grenache (G) grape varieties (From Garde-Cerdán et al. [5]).
3.1.5 C6 compounds
Figure 5 shows the results for C6 compounds in the control and the samples after each of the four treatments by PEF for the three grape varieties [5]. When these compounds are at low levels contribute positively to wine aroma; while, at high levels, they are responsible for herbaceous flavors [33].
The presence of (E)-2-hexen-1-ol in must samples of Treat1 of Graciano was diminished. However, Treat2 in Tempranillo enhanced the content of total C6 com- pounds, n-hexanol, (Z)-3-hexen-1-ol, and (E)-2-hexenal; while Treat1 decreased the content of hexanal. Treat1 in Grenache favored the presence of total C6 compounds and (Z)-3-hexen-1-ol. Also Treat1 and 3 enhanced the content of hexanal, and Treat2 favored the presence of (E)-2-hexenal. In general, and matching with the Comuzzo et al. [33] results, the PEF treatments hardly affected the amounts of C6 compounds.
The PEF samples increased of total C6 compounds in 72% after Treat1 in Grenache and 31% upon Treat2 in Tempranillo. On the other hand, the most abundant C6 compounds were in control samples accounting for 87%, 95%, and 91% in Graciano, Tempranillo, and Grenache respectively. The PEF treatments did not affect the rela- tive abundance of C6 compounds in must samples.
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Figure 4.
Esters average area in control and PEF treatments 1–4 in Graciano (Gr), Tempranillo (T), and Grenache (G) grape varieties (From Garde-Cerdán et al. [5]).
Pulsed Electric Fields as a Green Pretreatment to Enhance Mass Transfer from Grapes…
DOI: http://dx.doi.org/10.5772/intechopen.104609
3.2 Influence of PEF treatments on resveratrol and piceid content in Graciano,