Semi-quantitative analysis of volatile compounds in the headspace of GP wines

2.3.2.2.1. Riesling

The model wines, produced by supplementation of model must with individual grape berry tissues or whole berries and the subsequent fermentation of these mixtures, were analysed for their volatile compound composition. The complexity of the

chromatograms meant that a target list of compounds was chosen for quantification, based on compounds identified as being grape influenced in a previous study (Keyzers and Boss, 2010).

Table 17: Grape influenced aroma compounds that were not detected in GP Riesling wines

Target compounds not detected

aliphatics esters

(E)-2-nonenal 3-(methylthio)propyl acetate 2-pentadecanone 3-methylbutyl decanoate 2-undecanol ethyl (Z)-9-octadecenoate

ethyl heptanoate

terpenoids ethyl octadecanoate

α-farnesene octyl acetate

pentyl acetate

The list contained 101 Riesling target compounds, and 90 of these were detected in the headspace of the wines produced in this experiment. The 11 compounds that were not detected are listed in Table 17. Amongst the detected compounds, there were 21 compounds that were not significantly different in abundance between the treatments (Table 18) and 68 compounds that were found to be significantly different (p<0.05) in concentration amongst the wines (Table 19).

Table 18: Grape influenced aroma compounds that were not significantly different between GP Riesling wines

class

compound

aliphatics carboxylic acids meso-2,3-butanediol acetic acid 2-tridecanone

butanol dodecanoic acid

esters terpenoids

ethyl butanoate myrcene ethyl 3-methylbutanoate geranyl acetate

butyl acetate

3-methylbutyl acetate nor-isoprenoids methyl hexanoate vitispirane 2 ethyl hexanoate

ethyl nonanoate aromatics γ-butyrolactone benzyl alcohol 3-methylbutyl octanoate 2-phenylethanol ethyl 9-decenoate

ethyl undecanoate ethyl pentadecanoate

2.3.2.2.1.1. Overall comparison of the volatile composition of the wines from the experimental wines.

Only one compound differed between homogenised and crushed ‘whole berry’

wines, while 88 compounds were the same regardless of whether ‘whole berry’ tissue was homogenised or not prior to fermentation. The compound that differed was β-damascenone and it was found in higher concentrations in the crushed ‘whole berry’

wines compared to homogenised ‘whole berry’ wines.

There were 33 compounds that were significantly more concentrated in wines made from flesh than in wines made from skins and 49 compounds that were not significantly different (p>0.05) when comparing flesh-derived wines to skin-derived wines (Table 18 and Table 19). There were eight compounds that were more concentrated in

skin-derived wines than in flesh-skin-derived wines. These compounds were 3-ethoxypropanol, hexanol, (Z)-3-hexenol, ethyl acetate, ethyl (E)-3-hexenoate, heptyl acetate, α-terpinene and β-damascenone.

A total of 50 compounds were significantly more concentrated in wines made from flesh than in wines made from seeds (Table 19). There were 36 compounds that were not significantly different when flesh-derived wines were compared to wines made from seeds and four compounds that were more concentrated in wines made from seeds than in wines made from flesh. The compounds that were higher in seed-derived wines than in flesh-derived wines were 3-ethoxypropanol, ethyl acetate, heptyl acetate and

benzaldehyde.

Fifty-four compounds were not significantly different (p>0.05) when comparing skin-derived wines to seed-derived wines. Wines made from the fermentation of model must supplemented by skin tissue had a higher concentration of 29 compounds than wines made from seeds (Table 19). Wines made from seeds had higher concentrations than wines made from skins for six compounds: (E)-2-octenal, rac-2,3-butanediol, phenylethyl acetate, heptyl acetate, benzaldehyde and 3-ethoxypropanol.

When comparing wines made from crushed whole berries to wines made from individual tissues it was found that the crushed ‘whole berry’ wines had higher concentrations of; 27 compounds than wines made from skins, 52 compounds than wines made from seeds, and 7 compounds than wines made from flesh (Table 19). For the same comparisons with the wines made from crushed whole berries there was no significant difference in the concentrations of: 58 compounds for the flesh-derived wines, 58 compounds for the skin-derived wines, and 37 compounds for the seed-derived wines. Two compounds, ethyl hexadecanoate and (p)-vinylguaiacol, were more concentrated in flesh-derived wines than in crushed ‘whole berry’ wines. There were five compounds that were more concentrated in skin-derived wines than in wines made from crushed whole berries: ethyl acetate, heptyl acetate, β-damascenone,

(p)-vinylguaiacol and 3-ethoxypropanol. Two compounds were more highly concentrated in

wines made from seeds than in wines made from crushed whole berries: ethyl acetate and heptyl acetate.

Wines made from homogenised whole berries were also compared to wines made from individual tissues and did not significantly differ in the concentrations of: 73 compounds when compared to flesh-derived wines, 54 compounds when compared to skin-derived wines, and 45 compounds when compared to seed-derived wines. The homogenised ‘whole berry’ wines had higher concentrations of: nine compounds compared to flesh-derived wines, 31 compounds compared to skin-derived wines and 41 compounds compared to seed-derived wines. The nine compounds that were more highly concentrated in homogenised ‘whole berry’ wines than in flesh-derived wines were: 2-heptanone, 2-nonanol, linalool, benzaldehyde, hexanoic acid and four C6-compounds (hexanol, (E)-3-hexenol, (Z)-3-hexenol and (Z)-3-hexenyl acetate). Flesh-derived wines had higher concentrations of eight compounds than wines made from homogenised whole berries, namely, (E)-2-octenal, ethyl 3-(methylthio)propanoate, ethyl tetradecanoate, ethyl hexadecanoate, methyl decanoate, damascenone, β-farnesene and (p)-vinylguaiacol. There were five compounds that were more highly concentrated in wines made from skins than wines made from homogenised whole berries: 3-ethoxypropanol, ethyl acetate, heptyl acetate, β-damascenone and

(p)-vinylguaiacol, and three compounds were more concentrated in seed-derived wines than in wines made from homogenised whole berries: 3-ethoxypropanol, ethyl acetate and 2-methylpropyl acetate.

Table 19: Grape influenced aroma compounds that were significantly different between GP Riesling wines. The geometric means reported are the ratio of peak areas of the analyte and internal standard quantifier ions. Statistical similarity between means is indicated by values with the same letter in superscript (Tukey post-hoc).

geometric means (n=3)

Whole berry Whole berry

Compound Flesh Skin Seed (crushed) (homogenised)

aliphatics

2-heptanone 0.0363^B 0.0356^B 0.0566^AB 0.0818^A 0.0665^A

2-nonanone 0.126^A 0.0267^C 0.049^BC 0.0974^AB 0.107^A

2-undecanone 0.0203^A 0.00423^C 0.00652^BC 0.0110^AB 0.0144^AB 2-nonanol 0.0175^B 0.0063^C 0.00476^C 0.0294^AB 0.0334^A

octanol 0.0328^A 0.0138^B 0.00871^C 0.0380^A 0.0432^A

nonanol 0.0274^A 0.0115^B 0.00396^C 0.0425^A 0.0435^A

decanol 0.0107^A 0.00328^B 0.00217^B 0.0108^A 0.00904^A

dodecanol 0.0105^A 0.0029^AB 0.000396^B 0.00913^A 0.00576^A 2-methylpropanol 0.115^A 0.0681^BC 0.06^C 0.0870^AB 0.0901^AB

2-methylbutanol/3-methylbutanol 10.0^A 4.64^B 3.92^B 10.0^A 10.8^A

rac-2,3-butanediol 0.043^AB 0.0226^B 0.0951^A 0.0560^AB 0.0755^A 3-ethoxypropanol 0.0275^C 0.0892^B 0.21^A 0.0298^C 0.0351^C (E)-2-octenal 0.00764^A ND^D 0.00111^C 0.00323^AB 0.00302^B 3-(methylthio)propanol 0.048^A 0.000296^BC 0.000102^C 0.0178^A 0.00491^AB

hexanol 1.16^B 2.03^A 0.177^C 2.30^A 3.10^A

(E)-3-hexenol 0.0127^B 0.0104^B 0.000755^C 0.0185^AB 0.0333^A (Z)-3-hexenol 0.00294^B 0.0181^A 0.00149^C 0.0129^A 0.0155^A hexanal 0.00308^AB 0.00309^AB 0.00136^B 0.00648^A 0.00484^AB

esters

hexyl acetate 0.0106^A 0.00758^A 0.00308^B 0.0155^A 0.0114^A (Z)-3-hexenyl acetate 0.00631^B 0.00411^B 0.00109^C 0.0122^A 0.0126^A ethyl (E)-3-hexenoate 0.00267^BC 0.00613^A 0.00234^C 0.00446^AB 0.00361^ABC ethyl

3-(methylthio)propanoate 0.00411^A 0.000266^C ND^D 0.00207^AB 0.00100^B

ethyl acetate 1.13^B 2.98^A 3.64^A 0.947^B 0.597^B

ethyl 2-butenoate 0.0128^A 0.0021^B 0.00385^B 0.0238^A 0.0164^A

ethyl octanoate 9.03^A 3.4^C 3.82^BC 7.14^AB 5.01^ABC

ethyl decanoate 2.82^A 0.51^C 0.96^BC 2.26^A 1.90^AB

ethyl dodecanoate 0.185^A 0.0507^B 0.134^AB 0.152^AB 0.117^AB ethyl tetradecanoate 0.0094^A 0.00259^C 0.00253^C 0.00540^AB 0.00447^BC ethyl 3-hydroxytridecanoate 0.0267^A 0.0116^AB 0.00326^B 0.0258^A 0.0165^A ethyl hexadecanoate 0.00581^A 0.000193^C 0.000451^BC 0.000429^BC 0.000764^B methyl octanoate 0.0494^A 0.0107^BC 0.00858^C 0.0284^AB 0.0216^ABC methyl decanoate 0.0187^A 0.00389^C 0.00395^C 0.00975^AB 0.00759^BC ethyl phenylacetate 0.0303^A 0.00602^B 0.0154^AB 0.0227^A 0.0208^A phenylethyl acetate 0.854^A 0.137^B 0.544^A 1.08^A 0.731^A

geometric means (n=3)

Whole berry Whole berry

Compound Flesh Skin Seed (crushed) (homogenised)

2-methylpropyl acetate 0.0308^AB 0.0322^AB 0.0490^A 0.0206^AB 0.0124^B heptyl acetate 0.00438^C 0.0255^B 0.0724^A 0.00515^C 0.00487^C ethyl 2-furoate 0.0116^A 0.00437^B 0.000751^C 0.0140^A 0.0102^AB diethyl succinate 0.0599^A 0.0110^B 0.0150^B 0.0862^A 0.0584^A γ-nonalactone 0.0113^A 0.00913^A 0.00335^B 0.00639^AB 0.00585^AB 3-methylbutyl hexanoate 0.0304^A 0.00814^B 0.00823^B 0.0271^A 0.0206^A

carboxylic acids

hexanoic acid 1.17^B 0.660^C 0.626^C 1.69^A 1.65^A

octanoic acid 3.13^A 1.28^BC 0.817^C 2.31^AB 2.78^AB

nonanoic acid 0.0187^AB 0.0108^AB 0.00674^B 0.0168^AB 0.0213^A decanoic acid 1.11^A 0.221^BC 0.0949^C 0.501^AB 0.756^A

terpenoids

α-terpinene 0.00293^BC 0.0152^A 0.00147^C 0.0100^A 0.00680^AB limonene 0.000466^AB 0.00166^A 0.000228^B 0.00218^A 0.00144^A

ocimene 0.00113^A 0.00324^A ND^B 0.00261^A 0.00192^A

terpinolene 0.00186^A 0.00405^A ND^B 0.00374^A 0.00257^A

p-cymene 0.0277^A 0.0121^A 0.002^B 0.0383^A 0.0207^A

linalyl ethyl ether 0.00193^AB 0.00301^A 0.000718^B 0.00559^A 0.00502^A α-terpinyl ethyl ether 0.00234^A 0.00211^A 0.000159^B 0.00310^A 0.00234^A nerol oxide 0.0186^A 0.0127^A 0.000785^B 0.0231^A 0.0209^A geranyl ethyl ether 0.00637^A 0.00375^BC 0.00323^C 0.00498^AB 0.00582^A

linalool 0.0253^B 0.0279^B 0.00683^C 0.0691^A 0.101^A

hotrienol 0.084^A 0.02^B 0.00103^C 0.0766^A 0.0609^A

α-terpineol 0.00964^A 0.00939^A 0.00186^B 0.0210^A 0.0192^A β-citronellol 0.0187^A 0.0145^A 0.00538^B 0.0282^A 0.0203^A nerol 0.00141^A 0.000919^A 0.000379^B 0.00195^A 0.00161^A α-farnesene isomer 0.000856^A 0.000862^A 0.00017^B 0.000579^AB 0.000496^AB β-farnesene 0.00443^A 0.00358^ABC 0.00201^C 0.00381^AB 0.00243^BC nerolidol 0.00571^A 0.00197^B 0.000609^C 0.00352^AB 0.00308^AB

nor-isoprenoids

vitispirane 1 0.0113^AB 0.0133^AB 0.00044^B 0.0183^A 0.0148^AB riesling acetal 0.0114^A 0.0134^A 0.00038^B 0.0221^A 0.0153^A

1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) 0.00359^A 0.00227^A ND^B 0.00227^A 0.00104^A β-damascenone 0.0443^B 0.109^A 0.00583^D 0.0426^B 0.0232^C aromatics

benzaldehyde 0.0170^B 0.00929^C 0.0374^A 0.0276^AB 0.0389^A p-vinylguaiacol 0.00257^A 0.000409^B nd^C nd^C nd^C

2.3.2.2.1.2. Tissue-specific factors affected different classes of GP wine volatiles

2.3.2.2.1.3. Principal component analysis was performed on the GP Riesling wines.

To visualise spatially the relationship between the wines based on the volatile profiles and the association of volatile compounds with each wine a PCA was

performed. The first two principal components, PC-1 and PC-2, explained 59.06 % and 22.21 % of total variance, respectively. Together these components explained 81.27 % of total variance. PC-3 explained 14.88 % and the fourth component only explained 3.85 % of the variance, so were not considered important for further explaining the variance. A projection of compounds and tissues onto the factor space of PC-1 and PC-2 is shown in Figure 11.

Wines produced with seed tissue were correlated with high negative PC-1 scores.

On the right-hand side of the plot the ‘whole berry’ wines were located, although their positive PC-1 scores were not as high as the negative scores of the seed-derived wines.

Compounds that correlated (p-value<0.05) with high positive PC-1 loadings were:

terpenoids (hotrienol, nerolidol, geranyl ethyl ether, nerol oxide, nerol, and (p)-cymene), octanoic acid, nonanoic acid, octanol, nonanol, decanol, some branched chain alcohols and esters (methyl butanol and 3-methylbutanol, and 3-methylbutyl hexanoate), 2-phenylethyl butanoate, diethyl succinate, ethyl 2-furoate, hexyl acetate, and ethyl 3-hydroxytridecanoate. Compounds that correlated (p-value<0.05) with high negative PC-1 loadings were ethyl acetate, heptyl acetate, and 3-ethoxypropanol. In general, the volatile components of the wines were associated with positive PC-1 scores on the biplot, which co-localised with the ‘whole berry’-derived and flesh-derived wines (Figure 11).

There was some separation of the flesh-derived wines from the ‘whole berry’ wines,

component (Figure 11). Wines produced with skin tissue were correlated with high positive PC-2 scores, while wines made with flesh tissue were correlated with high negative PC-2 scores. (Z)-3-hexenol co-varied with high positive PC-2 loadings.

Figure 11: PCA bi-plots of PC-1 and PC-2 for GP Riesling wines and grape influenced aroma compounds. Abbreviations used in this figure are tabulated with their compound names in Table 11.

2.3.2.2.2. Cabernet Sauvignon

The volatile compound compositions of the Cabernet Sauvignon model wines produced using grape tissues in proportion to that seen in whole berries were analysed.

A target list of 115 compounds, which were those that changed with increasing percentage of Cabernet Sauvignon grape juice in wines of model must (Keyzers and

Boss, 2010), was used to focus the study on those compounds that may be influenced by grape composition.

Table 20: Grape influenced aroma compounds that were not detected in GP Cabernet Sauvignon wines

Target compounds not detected

aliphatics carboxylic acids

2-pentadecanone 2-ethylhexanoic acid

2-undecanol 9-decenoic acid

pentanol dodecanoic acid

esters terpenoids

2-heptyl acetate 2,3-dihydrofarnesol 2-methylpentyl acetate farnesol

3-(methylthio)propyl acetate farnesyl acetate 9-decnyl acetate β-citronellyl acetate

benzyl acetate

decyl acetate aromatics

ethyl (E)-2-hexenoate (p)-vinylguaiacol ethyl (Z)-9-octadecnoate

ethyl 3-(methylthio)propanoate others

ethyl octadecanoate 2-methyldihydro-3(2H)-thiophenone ethyl (E)-3-hexenoate

ethyl undecanoate

octyl acetate

propyl octanoate

2-ethylhexyl acetate

2.3.2.2.2.1. Most target compounds were detected, and most detected compounds significantly differed across the treatments.

Of the 115 Cabernet Sauvignon target compounds, 89 were detected in the

chromatograms and 26 were not detected (Table 20). Of the 89 compounds quantified in the wines, 18 did not differ significantly across the samples (p>0.05; Table 21), and 72 compounds were significantly different over the range of treatments (Table 22).

Table 21: Grape influenced aroma compounds that were not significantly different between GP Cabernet Sauvignon wines

class

compound

aliphatics esters

2-heptanone 2-methylpropyl octanoate 3-hydroxy-2-butanone 3-methylbutyl acetate dodecanol 3-methylbutyl butanoate

ethyl 2-furoate

carboxylic acids ethyl 3-methylbutanoate heptanoic acid ethyl 4-hydroxybutanoate

ethyl 9-decenoate terpenoids ethyl butanoate neryl propanoate ethyl nonanoate β-farnesene ethyl pentadecanoate

methyl dodecanoate

aromatics

benzothiazole

2.3.2.2.2.2. Most of the detected compounds did not differ significantly between homogenised and crushed ‘whole berry’ wines.

Most of the compounds (75 of 89) did not differ significantly (p>0.05) between homogenised and crushed ‘whole berry’ wines. Crushed ‘whole berry’ wines were higher in abundance than homogenised ‘whole berry’ wines for three analytes; 2-phenylethanol, acetic acid and 2-methylbutanol/3-methylbutanol. There were 11 compounds that were higher in homogenised ‘whole berry’ wines than in crushed

‘whole berry’ wines; ethyl dodecanoate, ethyl tetradecanoate, ethyl hexadecanoate, ethyl 9-hexadecenoate, 3-methylbutyl decanoate, 3-methylbutyl dodecanoate, 1-octen-3-ol, (Z)-3-hexenyl acetate, (Z)-2-heptenal, 2-methylpropanol and propanol.

Of the wines produced from grape berry tissues, flesh-derived wines and skin-derived wines appeared to be most similar as 56 compounds were not significantly different in these wines. Twenty-two compounds were significantly more concentrated in wines made from flesh than in wines made from skins and seven analytes that were more concentrated in skin-derived wines than in flesh-derived wines (Table 22).

When the berry tissue wines are compared, the greatest number of significant differences was seen between the wines made from flesh and the wines made from seeds. A total of 32 compounds were significantly more concentrated in wines made from flesh than in wines made from seeds and 19 compounds were more concentrated in wines made from seeds than in wines made from flesh. There were 38 compounds that were not significantly different when flesh-derived wines were compared to wines made from seeds.

Forty-three compounds were not significantly different when comparing skin-derived wines to seed-skin-derived wines. Wines made from the fermentation of model must supplemented by skin tissue had a higher concentration of 30 compounds than wines made from seeds whereas; wines made from seeds had higher concentrations than wines made from skins for 16 compounds.

Given that the whole berries are mainly made of flesh (Table 5), we might expect that the ‘whole berry’ wines are most similar to those made from flesh. This was indeed the case as when wines made from crushed whole berries were compared to wines made from individual tissues there was no significant difference in the concentrations of: 67 compounds for flesh-derived wines, 54 compounds for skin-derived wines, and 30 compounds for seed-derived wines. Similarly, the wines made from homogenised whole berries did not significantly differ in the concentrations of: 56 compounds when

compared to flesh-derived wines, 41 compounds when compared to skin-derived wines, and 29 compounds when compared to seed-derived wines. Wines made from crushed whole berries had higher concentrations of; 17 compounds than wines made from flesh, 31 compounds than wines made from skins and 41 compounds than wines made from seeds. Wines made from homogenised whole berries had higher concentrations of: 29 compounds than flesh-derived wines, 42 compounds than skin-derived wines and 46

derived wines than in crushed ‘whole berry’ wines: 2-methylpropanol,

3-ethoxypropanol, 3-(methylthio)propanol and phenylethyl acetate. Three of these compounds (3-ethoxypropanol, 3-(methylthio)propanol and phenylethyl acetate) were also more concentrated in flesh-derived wines compared to wines made from

homogenised whole berries, and, acetic acid also followed this pattern (Table 22Table 22). There were four compounds that were more highly concentrated in skin-derived wines than in wines made from crushed whole berries: methylpropanol, ethyl methylpropanoate, acetic acid and methylpropanoic acid. The concentrations of 2-methylpropanol, ethyl 2-methylpropanoate and acetic acid were also higher in the skin-derived wines than the homogenised ‘whole berry’ wines along with,

2-methylbutanol/3-methylbutanol, and 2-phenylethanol. A total of 18 compounds were more highly concentrated in wines made from seeds than in wines made from crushed whole berries while 14 compounds were more concentrated in seed-derived wines than in wines made from homogenised whole berries.

Table 22: Grape influenced aroma compounds that were significantly different between GP Cabernet Sauvignon wines. Geometric means are reported and derived from ratio of the peak area of the quantifier ion for that compound divided by the peak area of the quantifier ion for the relevant internal standard. Statistical similarity between means is indicated by values with the same letter in superscript (Tukey post-hoc).

geometric means (n=3)

Whole berry Whole berry

Compound Flesh Skin Seed (crushed) (homogenised)

aliphatics

2-nonanone 0.172^A 0.165^AB 0.0968^B 0.221^A 0.250^A

2-undecanone 0.0403^B 0.0281^C 0.0165^D 0.0484^AB 0.0577^A

propanol 0.115^D 0.102^E 0.633^A 0.126^C 0.136^B

butanol 0.061^B 0.0459^C 0.0335^D 0.116^A 0.118^A

2-heptanol 0.00236^B 0.00302^B 0.0028^B 0.00592^A 0.00646^A 1-octen-3-ol 0.0459^B 0.0312^C 0.0687^A 0.0506^B 0.0714^A

heptanol 0.0411^B 0.0732^A 0.0398^B 0.0801^A 0.0908^A

2-nonanol 0.0607^BC 0.0561^C 0.0326^D 0.0906^A 0.0813^AB

octanol 0.047^B 0.0401^C 0.0256^D 0.0706^A 0.0726^A

decanol 0.0295^A 0.0166^B 0.00526^C 0.0343^A 0.0325^A

geometric means (n=3)

Whole berry Whole berry

Compound Flesh Skin Seed (crushed) (homogenised)

2-methylpropanol 0.174^C 0.339^A 0.202^B 0.136^D 0.166^C 3-ethoxypropanol 0.0486^B 0.0267^D 0.148^A 0.0381^C 0.0339^C

2-methylbutanol/3-methylbutanol 3.32^D 11.1^B 13.3^A 10.6^B 7.66^C

3-octanone 0.0143^AB 0.00753^C 0.0182^A 0.0121^B 0.0143^AB (E)-2-heptenal 0.0000436^C 0.0000455^C 0.000938^AB 0.000328^B 0.00324^A rac-2,3-butanediol 0.19^AB 0.0936^B 0.258^A 0.296^A 0.322^A meso-2,3-butanediol 0.0716^AB 0.0514^B 0.109^A 0.0962^AB 0.130^A

3-(methylthio)propanol 0.215^A 0.0519^C 0.000671^D 0.136^B 0.150^B

hexanol 0.993^B 1.24^B 0.0856^C 2.17^A 2.60^A

(E)-3-hexenol 0.0107^B 0.0155^AB 0.000328^C 0.0213^AB 0.0261^A (Z)-3-hexenol 0.00259^A 0.0101^A 0.000475^B 0.00702^A 0.0099^A hexanal 0.00331^A 0.00196^AB 0.000903^B 0.00307^A 0.00406^A

esters

hexyl acetate 0.00558^B 0.00589^B 0.00256^C 0.00947^AB 0.0133^A (Z)-3-hexenyl

acetate 0.00261^AB 0.00207^B ND^C 0.00247^B 0.00352^A

ethyl acetate 0.924^B 1.19^B 3.79^A 1.08^B 1.13^B

ethyl propanoate 0.0223^B 0.0199^B 0.0872^A 0.0197^B 0.0265^B ethyl 2-butenoate 0.0113^B 0.00637^C 0.00323^D 0.0163^A 0.0159^A

ethyl hexanoate 2.44^B 2.44^B 3.45^AB 4.12^AB 4.76^A

ethyl heptanoate 0.00754^B 0.0129^AB 0.029^A 0.0111^B 0.0144^AB

ethyl octanoate 4.86^BC 4.06^C 4.72^BC 7.65^AB 8.57^A

ethyl decanoate 2.19^A 1.04^B 0.889^B 2.86^A 2.82^A

ethyl dodecanoate 0.236^B 0.110^C 0.341^B 0.334^B 0.735^A ethyl tetradecanoate 0.00916^BC 0.00602^C 0.0115^BC 0.0137^B 0.0405^A ethyl

hexadecanoate 0.0109^B 0.00406^C 0.00371^C 0.0146^B 0.0422^A ethyl

9-hexadecenoate 0.00163^B 0.000519^BC 0.000402^C 0.0015^B 0.00533^A 3-methylbutyl

hexanoate 0.0203^BC 0.0118^CD 0.00646^D 0.03^AB 0.0423^A 3-methylbutyl

octanoate 0.00676^AB 0.00272^C 0.00544^BC 0.0106^AB 0.0146^A 3-methylbutyl

decanoate 0.0589^BC 0.037^C 0.075^B 0.0651^B 0.154^A

3-methylbutyl

dodecanoate 0.00347^B 0.00291^B 0.0044^B 0.00559^B 0.0175^A ethyl

2-methylpropanoate 0.00343^BC 0.00838^AB 0.00911^A 0.00184^C 0.00278^C propyl acetate 0.00775^B 0.00638^B 0.0861^A 0.00637^B 0.00781^B 2-methylpropyl

acetate 0.0123^B 0.0283^AB 0.0496^A 0.0127^B 0.0168^B

butyl acetate 0.00198^C 0.00252^BC 0.00583^A 0.00316^BC 0.00364^AB pentyl acetate 0.0167^A 0.0226^A 0.00712^B 0.0344^A 0.018^A propyl hexanoate 0.00108^CD 0.000916^D 0.0092^A 0.00211^BC 0.00294^B heptyl acetate 0.00324^B 0.00254^B 0.0158^A 0.00259^B 0.00256^B methyl decanoate 0.00616^B 0.00326^C 0.00155^D 0.0102^A 0.00807^AB diethyl succinate 0.129^A 0.123^A 0.0684^B 0.142^A 0.137^A

geometric means (n=3)

Whole berry Whole berry

Compound Flesh Skin Seed (crushed) (homogenised)

ethyl phenylacetate 0.0751^A 0.024^B 0.0142^C 0.0621^A 0.0601^A phenylethyl acetate 1.38^A 0.289^C 0.324^C 0.533^B 0.579^B 2-phenylethyl

octanoate 0.00357^AB 0.00124^C 0.00189^BC 0.00421^A 0.00684^A

carboxylic acids

acetic acid 0.162^C 0.415^B 0.636^A 0.166^C 0.105^D

butanoic acid 0.0478^B 0.0497^B 0.0513^B 0.0704^A 0.0708^A

hexanoic acid 0.847^B 0.687^C 0.495^D 1.18^A 1.18^A

octanoic acid 1.3^A 0.728^B 0.289^C 1.72^A 1.87^A

decanoic acid 0.0831^AB 0.0876^AB 0.0499^B 0.19^A 0.141^AB 2-methylpropanoic

acid 0.0344^C 0.0737^A 0.0523^B 0.0309^C 0.0326^C

terpenoids

linalool 0.0257^AB 0.0136^C 0.0192^BC 0.032^A 0.0324^A

geranyl acetate 0.0211^A 0.0141^B 0.00604^C 0.0219^A 0.017^AB β-citronellol 0.0375^B 0.0265^C 0.0168^D 0.0462^A 0.0436^AB nerol 0.00157^B 0.00129^B 0.000749^C 0.00247^A 0.00261^A geraniol 0.0417^A 0.0137^AB 0.00649^B 0.0493^A 0.0389^A α-farnesene isomer 0.000813^A 0.00121^A 0.000608^A 0.000986^A 0.000605^A nerolidol 0.00866^A 0.00694^A 0.00281^B 0.0108^A 0.0078^A cadalene ND^B 0.0000312^AB 0.000127^A 0.000287^A 0.000269^A

nor-isoprenoids

β-damascenone 0.071^A 0.0394^A 0.00394^B 0.0748^A 0.0406^A

aromatics

benzyl alcohol 0.00345^C 0.00789^B 0.00163^D 0.0214^A 0.0211^A

2-phenylethanol 0.215^C 1.47^AB 1.71^A 1.22^B 0.438^C

phenol 0.00412^AB 0.00343^BC 0.00285^C 0.00461^A 0.00477^A benzophenone 0.000413^A 0.000183^A 0.000023^B 0.000235^A 0.000391^A benzaldehyde 0.0369^A 0.0457^A 0.0269^B 0.0483^A 0.0483^A

2.3.2.2.2.3. Different classes of compounds have varying reliance on grape berry tissue for their production during winemaking

2.3.2.2.2.4. Principal component analysis of Cabernet Sauvignon model wines.

Visualisation of the relationship between the wines based on the volatile profiles was achieved by conducting a principal components analysis using the compounds significantly different in the wine samples. PC-1 explained 62.21 % of the total

variance, and PC-2 explained 22.22 % of the total variance meaning that these first two principal components explained 84.42 % of total variance. The next two principal components, PC-3 and PC-4 explained 9.86 % and 5.72 % of total variance, respectively. Figure 12 shows a biplot projection of the pre-analysis loadings for variables and scores for tissues onto the factor space of the first two components.

The location of the different wine samples in the PCA biplot is similar to that seen in the corresponding Riesling experiment (Figure 11). Wines made with seed tissue had highly negative PC-1 scores, while wines that were made with whole homogenised berries had highly positive PC-1 scores. The crushed berry wine samples were also found on the right-hand side of the plot, but the PC-1 scores for these wines were not as high as those of the homogenised ‘whole berry’ wines. The wines made from seeds had negative PC-1 scores and hence were found on the left-hand side of the plot. The variability in the volatile profiles of the flesh-derived wines were not well described by PC-1. Compounds that had highly positive PC-1 loadings (p-value<0.05) were: ethyl decanoate, C6 compounds (hexanol, hexanal, (E)-3-hexenol, hexyl acetate and (Z)-3-hexenyl acetate), terpenoids (geraniol, nerol, and β-citronellol), free fatty acids

(hexanoic acid and octanoic acid), 3-methybutyl hexanoate, aliphatic alcohols (butanol, octanol, 2-nonanol and decanol), phenol, 2-nonanone, methyl decanoate, and diethyl succinate. Compounds with highly negative PC-1 loadings were: isobutyric acid, its ethyl ester, and acetic acid.

Wines made with seed and whole homogenised berries had high positive with PC-2 scores, while wines made with skin tissue had PC-2 scores that were highly negative.

Homogenised ‘whole berry’ wines were also found in the upper half of the biplot, indicating they had positive PC-2 scores, whereas the flesh-derived wines had negative PC-2 scores. The variation in the profiles of the crushed ‘whole berry’ wines was not

well described by PC-2 (Figure 12). Compounds that highly correlated with large positive PC-2 loadings were meso-2,3-butanediol and 1-octen-3-ol.

Figure 12: PCA bi-plots of PC-1 and PC-2 for GP Cabernet Sauvignon wines and grape influenced aroma compounds. Abbreviations used in this figure are tabulated with their compound names in Table 11.

2.4. Discussion

The experiments described in this chapter were designed to explore the grape tissue-specific origin of wine volatiles. There have been some studies that have explored localisation of grape volatiles or precursors linked to grape-derived wine volatiles, such as methoxypyrazines (Dunlevy et al., 2013), monoterpene polyols (Williams et al., 1980), glycosylated monoterpenes (Wilson et al., 1986), cysteine- or glutathione-bound thiols (Peyrot des Gachons et al., 2002, Murat et al., 2001), and phenolic acids (Pinelo

et al., 2006). Some studies have investigated the role of varying skin contact or skinless fermentations on isoamyl acetate, FAEE, 2-phenylethanol and 2-phenylethyl acetate (Callejón et al., 2012). However, to our knowledge, the potential roles of different grape tissues on many grape-derived and fermentation-derived volatile compounds have not been fully explored. To explore the grape tissue-specific origins of wine volatiles, two

et al., 2006). Some studies have investigated the role of varying skin contact or skinless fermentations on isoamyl acetate, FAEE, 2-phenylethanol and 2-phenylethyl acetate (Callejón et al., 2012). However, to our knowledge, the potential roles of different grape tissues on many grape-derived and fermentation-derived volatile compounds have not been fully explored. To explore the grape tissue-specific origins of wine volatiles, two

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