Table 4 The volatile aroma compounds detected and measured in the samples collected from different spatial positions of fermented grain

Volatile acids

AC1

Acetic acid

MS, RI

2.535 ± 0.125a

5.287 ± 0.258b

8.387 ± 0.312c

AC2

Propionic acid

MS, RI

0.765 ± 0.114a

2.154 ± 0.127b

4.154 ± 0.205c

AC3

Butyric acid

MS, RI

1.163 ± 0.054a

2.854 ± 0.241b

4.676 ± 0.302c

AC4

Caproic acid

MS, RI

1.167 ± 0.126a

3.951 ± 0.235b

6.765 ± 0.478c

AC5

3-methyl-pentanoic acid

MS, RI

0.000a

0.625 ± 0.068b

0.958 ± 0.056c

AC6

2-methyl-butanoic acid

MS, RI

0.000a

0.487 ± 0.084b

1.254 ± 0.214c

AC7

Octanol acid

MS, RI

0.120 ± 0.015a

0.127 ± 0.016a

0.234 ± 0.024b

AC8

2-Methyl butanoic acid

MS, RI

0.102 ± 0.018a

0.312 ± 0.028b

0.425 ± 0.036c

AC9

Pentanoic acid

MS, RI

0.212 ± 0.019a

0.247 ± 0.021a

0.257 ± 0.026a

AC10

Nonanoic acid

MS, RI

0.117 ± 0.019a

0.215 ± 0.026b

0.250 ± 0.035b

AC11

Hexanoic acid

MS, RI

0.112 ± 0.010a

0.117 ± 0.013a

0.225 ± 0.012b

AC12

Palmitic acid

MS, RI

0.323 ± 0.056a

0.368 ± 0.038a

0.389 ± 0.040a

AC13

Octanoic acid

MS, RI

0.035 ± 0.008a

0.126 ± 0.016a

0.225 ± 0.201a

AC14

Decanoic acid

MS, RI

0.087 ± 0.005a

0.158 ± 0.021b

0.299 ± 0.015c

Σ

6.738 ± 0.102

17.028 ± 0.189

28.498 ± 0.313

Esters

ES1

Ethyl acetate

MS, RI

6.465 ± 0.987a

10.325 ± 1.023b

16.421 ± 1.213

ES2

Ethyl isobutanoat

MS, RI

0.287 ± 0.014a

1.743 ± 0.214b

0.712 ± 0.052c

ES3

Ethyl butanoate

MS, RI

0.353 ± 0.068a

1.557 ± 0.168b

2.832 ± 0.254c

ES4

Ethyl hexanoate

MS, RI

4.725 ± 0.365a

8.876 ± 1.021b

17.154 ± 1.232c

ES5

Ethyl oenanthate

MS, RI

0.435 ± 0.032a

0.792 ± 0.058b

1.526 ± 0.140c

ES6

Ethyl 2-methylbutanoate

MS, RI

0.526 ± 0.023a

1.158 ± 0.101b

1.988 ± 0.187c

ES7

Ethyl 3-methylbutanoate

MS, RI

0.468 ± 0.036a

1.025 ± 0.124b

1.854 ± 0.112c

ES8

Nonanoic acid ethyl ester

MS, RI

0.821 ± 0.054a

1.287 ± 0.068b

2.321 ± 0.096c

ES9

Ethyl decanoate

MS, RI

1.053 ± 0.036a

1.087 ± 0.057a

0.993 ± 0.065a

ES10

Ethyl heptanoate

MS, RI

1.024 ± 0.152a

2.012 ± 0.185b

3.214 ± 0.220c

ES11

Benzeneacetic acid ethyl ester

MS, RI

1.587 ± 0.702a

1.256 ± 0.075a

1.032 ± 0.065a

ES12

Ethyl laurate

MS, RI

1.021 ± 0.098a

1.512 ± 0.103b

1.997 ± 0.121c

ES13

γ-nonylactone

MS, RI

0.432 ± 0.036a

0.556 ± 0.045b

0.952 ± 0.051c

ES14

Ethyl oleate

MS, RI

4.337 ± 0.401a

4.258 ± 0.398a

4.361 ± 0.385a

ES15

Ethyl pentadecanoate

MS, RI

3.668 ± 0.258a

3.174 ± 0.261b

2.189 ± 0.187c

ES16

Ethyl 9-hexadecenoate

MS, RI

3.327 ± 0.257a

3.418 ± 0.264a

3.032 ± 0.213a

ES17

Ethyl palmitate

MS, RI

5.698 ± 0.445a

5.735 ± 0.406a

5.676 ± 0.412a

ES18

Ethyl linoleate

MS, RI

4.977 ± 0.235a

4.985 ± 0.236a

5.034 ± 0.239a

ES19

Ethyl octadecanoate

MS, RI

1.254 ± 0.132a

2.145 ± 0.201b

3.210 ± 0.254c

Σ

42.458 ± 0.875

56.901 ± 0.497

76.498 ± 0.687

Alcohols

AL1

3-methyl-butanol

MS, RI

0.352 ± 0.065a

0.732 ± 0.045b

1.597 ± 0.036c

AL2

Isoamyl alcohol

MS, RI

1.523 ± 0.116a

0.736 ± 0.085b

0.474 ± 0.036c

AL3

1-hexanol

MS, RI

0.226 ± 0.036a

0.276 ± 0.028ab

0.197 ± 0.027b

AL4

2-methyl-1-propanol

MS, RI

0.215 ± 0.036a

0.621 ± 0.045b

0.889 ± 0.061c

AL5

1-octen-3-ol

MS, RI

0.688 ± 0.052a

0.379 ± 0.029b

0.223 ± 0.028c

AL6

Isobutanol

MS, RI

0.215 ± 0.018a

0.356 ± 0.031b

0.625 ± 0.048c

AL7

Enanthol

MS, RI

0.263 ± 0.021a

0.255 ± 0.019a

0.275 ± 0.018a

AL8

Isooctanol

MS, RI

0.389 ± 0.028a

0.279 ± 0.019b

0.201 ± 0.017c

AL9

1-Butanol

MS, RI

0.158 ± 0.015a

0.268 ± 0.021b

0.441 ± 0.034c

AL10

2,3-butanediol

MS, RI

0.000a

1.525 ± 0.102b

3.085 ± 0.231c

AL11

Octanol

MS, RI

0.378 ± 0.027a

0.204 ± 0.019b

0.125 ± 0.014c

AL12

2-Methylbutanol

MS, RI

0.000a

1.131 ± 0.132b

2.231 ± 0.242c

AL13

Isopentanol

MS, RI

1.257 ± 0.015a

0.654 ± 0.026b

0.364 ± 0.017c

AL14

1-Pentanol

MS, RI

0.357 ± 0.028a

0.674 ± 0.045b

1.025 ± 0.103c

AL15

1-nonanol

MS, RI

0.232 ± 0.031a

0.167 ± 0.013a

0.154 ± 0.018b

AL16

2-Heptanol

MS, RI

0.126 ± 0.023a

0.265 ± 0.019b

0.398 ± 0.025c

AL17

Benzyl alcohol

MS, RI

0.929 ± 0.058a

0.631 ± 0.054b

0.356 ± 0.026c

AL18

Phenylethyl alcohol

MS, RI

0.000a

2.351 ± 0.215b

5.705 ± 0.498c

Σ

7.308 ± 0.081

11.504 ± 0.098

18.365 ± 0.254

Aldehydes

AD1

2-Heptenal

MS, RI

0.315 ± 0.029a

0.267 ± 0.025b

0.132 ± 0.012c

AD2

Nonaldehyde

MS, RI

0.164 ± 0.015a

0.187 ± 0.013b

0.116 ± 0.012b

AD3

Benzaldehyde

MS, RI

1.267 ± 0.015a

2.336 ± 0.035b

0.363 ± 0.021c

AD4

2-undecenal

MS, RI

0.278 ± 0.027a

0.857 ± 0.068b

0.101 ± 0.011c

AD5

Pentanal

MS, RI

0.317 ± 0.026a

0.399 ± 0.038a

0.267 ± 0.019b

AD6

2-phenyl-2-butenal

MS, RI

1.632 ± 0.032a

1.276 ± 0.017b

2.223 ± 0.021c

Σ

3.973 ± 0.025

5.322 ± 0.031

3.202 ± 0.014

Ketones

KE1

2-octanone

MS, RI

1.903 ± 0.112a

2.231 ± 0.118b

1.412 ± 0.116c

KE2

2-nonanone

MS, RI

0.182 ± 0.017a

0.262 ± 0.026a

0.179 ± 0.016b

Σ

2.085 ± 0.562

2.493 ± 0.601

1.591 ± 0.573

Alkanes

AK1

Decamethylcyclopentasiloxane

MS, RI

0.215 ± 0.021a

0.826 ± 0.045b

0.616 ± 0.057c

AK2

Tetradecane

MS, RI

0.513 ± 0.046a

0.757 ± 0.037a

0.512 ± 0.045b

AK3

Pentadecane

MS, RI

1.761 ± 0.116a

1.451 ± 0.116b

1.782 ± 0.124b

AK4

Caryophyllene

MS, RI

1.021 ± 0.012a

2.357 ± 0.023b

0.669 ± 0.063c

AK5

Hexadecane

MS, RI

0.587 ± 0.038a

1.383 ± 0.054b

0.798 ± 0.062c

Σ

4.097 ± 0.054

6.774 ± 0.041

4.377 ± 0.058

Volatile phenols

VP1

Phenol

MS, RI

0.185 ± 0.019a

0.875 ± 0.013b

0.231 ± 0.014c

VP2

2-Methoxy-4-vinylphenol

MS, RI

0.000a

0.275 ± 0.035b

0.426 ± 0.062c

Σ

0.185 ± 0.019

1.15 ± 0.029

0.657 ± 0.054