Table 2.
Identified volatile compounds in unfermented and fermented plant-based milks, aroma attributes, odour groups, and the odour threshold in air
| Nr | Compound namea | RI, cal (min) | Aroma description | Odour groupb | Odour threshold (ppbv) | Identification |
|---|---|---|---|---|---|---|
| Aldehydes | ||||||
| 1 | 3-Methyl-butanal | 648 | Malty, fatty, cocoa, fruity | 1 | 11 | MS, RI |
| 2 | 2-Methyl-butanal | 654 | Malty, cocoa | 1 | 11 | MS, RI |
| 3 | Hexanal | 799 | Green, grassy, nutty, fat, oxidized oil | 6 | 0.28 | MS, STD, RI |
| 4 | 2,4-Heptadienal3 | 1010 | Fatty, creamy, green | 3 | 8 | MS, RI |
| 5 | 2-Heptenal | 957 | Green, fatty | 6 | 19 | MS, RI |
| 6 | Heptanal | 904 | Green, citrus, fatty, floral, rancid | 6 | 0.18 | MS, STD, RI |
| 7 | Benzaldehyde | 959 | Sweet, fruity, almond | 1 | 20 | MS, STD, RI |
| 8 | 2-Octenal | 1058 | Fatty | 3 | 0.53 | MS, RI |
| 9 | Phenylacetaldehyde | 1043 | Floral, sweet, honey | 2 | 4 | MS, STD, RI |
| 10 | 4-Ethyl-benzaldehyde | 1161 | Fruity | 1 | 13 | MS, RI |
| 11 | 2-Nonenal | 1158 | Green, musty, fatty, | 6 | 0.02 | MS, RI |
| 12 | Nonanal | 1103 | Citrus, floral, fatty, green, smoky | 1 | 0.34 | MS, STD, RI |
| 13 | 2,4-Decadienal4 | 1312 | Grass, fatty, melon, aldehyde | 6 | 0.07 | MS, RI |
| 14 | Decanal | 1202 | Fatty, floral | 3 | 0.10 | MS, RI |
| Alcohols | ||||||
| 1 | [S, S]-2,3-Butanediol1,2 | 780 | Creamy, buttery | 3 | 49 | MS, RI |
| 2 | 3-Methyl-2-buten-1-ol 2 | 773 | Fruity | 1 | 173 | MS, RI |
| 3 | 3-Methyl-1-butanol 2,4 | 733 | Fruity, banana, whiskey, floral, fermented | 1 | 68 | MS, RI |
| 4 | 2-Methyl-1-butanol 1,4 | 734 | Ethereal, floral | 1 | 68 | MS, RI |
| 5 | 1-Pentanol | 765 | Fermented, sweet, fruity, balsamic, alcoholic | 1 | 43 | MS, STD, RI |
| 6 | 1-Hexanol | 869 | Fruity, lemon | 1 | 6 | MS, STD, RI |
| 7 | 2-Heptanol1,3,4 | 900 | Citrus, fruity, herbal | 1 | 41 | MS, RI |
| 8 | 1-Heptanol | 970 | Light green, mushroom, rancid | 6 | 3 | MS, STD, RI |
| 9 | Benzyl alcohol2,3 | 1033 | Floral | 2 | 1 × 104 | MS, RI |
| 10 | 2-Methyl-3-hexanol1 | 859 | Unknown | 9 | MS, RI | |
| 11 | Phenylethyl alcohol2,4 | 1112 | Floral, rose, honey | 2 | 0.02 | MS, STD, RI |
| 12 | 1-Octen-3-ol | 979 | Earthy, mushroom | 7 | 0.52 | MS, RI |
| 13 | 2-Octen-1-ol1,2,3,4 | 1067 | Cucumber | 2 | 40 | MS, RI |
| 14 | 3-Octanol4 | 996 | Earthy | 7 | 27 | MS, RI |
| 15 | 2-Ethyl-1-hexanol4 | 1028 | Citrus, floral | 1 | 130 | MS, RI |
| 16 | 1-Octanol | 1070 | Waxy, aldehyde, fruity, floral | 3 | 2.7 | MS, RI |
| 17 | 1-Nonanol2,4 | 1171 | Citrus, rose | 1 | 0.9 | MS, RI |
| 18 | Eugenol4 | 1368 | Pleasant spicy, clove-like | 2 | 6 | MS, STD, RI |
| 19 | Cherry-propanol | 1183 | Fruity | 1 | MS, RI | |
| 20 | Trans-pinocarveol | 1138 | Woody, balsamic | 5 | MS, RI | |
| 21 | cis-Verbenol | 1166 | Balsamic, pine | 5 | MS, RI | |
| 22 | (-)-Myrtenol | 1195 | Woody, minty, camphoraceous | 5 | 0.32 | MS, RI |
| 23 | Myrtenol | 1203 | Woody, herbal, floral | 5 | 0.32 | MS, RI |
| 24 | Linalool | 1100 | Floral, fruity | 2 | 4 | MS, RI |
| 25 | Terpinen-4-ol | 1176 | Balsamic, woody, green, fatty, fruity, floral, spicy | 5 | 150 | MS, RI |
| 26 | 3-Ethyl-4-nonanol2,3 | 1094 | Unknown | 9 | MS, RI | |
| Ketones | ||||||
| 1 | Methyl-vinyl-ketone | 734 | Pungent, sweet | 8 | MS | |
| 2 | 2,3-Butanedione2,3,4 | 440 | Buttery, sweet, creamy | 3 | 0.3 | MS, RI |
| 3 | 3-Hydroxybutan-2-one2,4 | 706 | Buttery, creamy, sweet, toasted | 3 | 0.3 | MS, RI |
| 4 | 2,3-Pentanedione3 | 694 | Buttery, sweet | 3 | 12 | MS, RI |
| 5 | 2-Hexanone1, 2 | 800 | Fruity | 1 | 24 | MS, RI |
| 6 | 2,3-Heptanedione1 | 836 | Buttery | 3 | MS, RI | |
| 7 | 3,6-Heptanedione2 | 1062 | Buttery | 3 | MS, RI | |
| 8 | 2-Heptanone | 891 | Fruity, floral, sweet, cheesy | 1 | 0.76 | MS, RI |
| 9 | 1-(2-Furanyl)-1-propanone2 | 1031 | Fruity | 1 | MS, RI | |
| 10 | 3,5-Octadien-2-one | 1092 | Fruity, fatty, green, earthy | 1 | 5 | MS, RI |
| 11 | 6-Methyl-5-hepten-2-one3 | 987 | Citrus, musty, green | 1 | 1 | MS, RI |
| 12 | 5-Methyl-3-hepten-2-one | 1039 | Unknown | 9 | MS, RI | |
| 13 | 3-Octanone4 | 987 | Earthy [1], mushroom-like [3], fresh [3], herbal [3], ripe banana [3] | 7 | 21 | MS, RI |
| 14 | Isoacetovanillone | 1158 | Unknown | 9 | MS, RI | |
| 15 | 2-Nonanone4 | 1091 | Sweet, fruity, floral, green, hot milk, soap | 1 | 5 | MS, RI |
| 16 | 5,6-Dehydrocamphor | 1095 | Unknown | 9 | MS, RI | |
| 17 | Pinocarvone | 1162 | Camphoraceous, fresh | 5 | MS, RI | |
| 18 | D-Verbenone | 1208 | Camphoraceous, minty, spicy | 5 | MS, RI | |
| Organic acids | ||||||
| 1 | Acetic acid1,2,3,4 | 401 | Acidic, sour, vinegar | 4 | 6 | MS, STD, RI |
| 2 | 3-Methyl-butanoic acid1,3 | 843 | Cheesy | 4 | 0.08 | MS, RI |
| 3 | 2-Methyl-butanoic acid2,3 | 853 | Sour, cheesy, fermented | 4 | 0.04 | MS, RI |
| 4 | Pentanoic acid1 | 882 | Cheesy, acidic, unpleasant | 4 | 8.90 | MS, RI |
| 5 | Hexanoic acid2,3 | 982 | Cheesy, fatty, sour, sharp, rancid | 4 | 0.60 | MS, RI |
| 6 | Octanoic acid2,3 | 1167 | Cheesy, fatty, sweaty | 4 | 27 | MS, RI |
| 7 | Nonanoic acid | 1269 | Waxy, earthy | 3 | 1.9 | MS, RI |
| Esters | ||||||
| 1 | Ethylacetate | 916 | Sweet, fruity, mild | 1 | 870 | MS, RI |
| 2 | Ethyllactate1 | 791 | Fruity, buttery | 1 | 5 × 104 | MS, RI |
| 3 | Ethyl 2-methylbutyrate | 850 | Fruity | 1 | 0.01 | MS, RI |
| 4 | Hexyl acetate | 1014 | Fruity, sweet | 1 | 1.8 | MS, RI |
| 5 | Verbenylacetate | 1144 | Unknown | 9 | MS, RI | |
| 6 | Bornyl acetate2 | 1201 | Balsamic, camphoraceous | 5 | 75 | MS |
| 7 | Epoxy-alpha-terpenylacetate | 1130 | Unknown | 9 | MS, RI | |
| Furans | ||||||
| 1 | 2-Ethyl-furan3 | 699 | Chemical, sweet, coffee-like | 8 | 1.3 × 106 | MS, RI |
| 2 | 2-Ethyl-5-methylfuran2 | 773 | Grassy | 8 | MS, RI | |
| 3 | 2-Acetyl-5-methylfuran | 855 | Nutty | 5 | MS, RI | |
| 4 | 2-n-Butyl furan1 | 892 | Spicy, fruity, wine-like | 8 | 1 × 105 | MS, RI |
| 5 | 2-(1-Pentenyl)-furan3 | 1001 | Roasted | 5 | MS, RI | |
| 6 | 2-Pentyl-furan | 991 | Beany, green, grassy, nutty, fatty | 6 | 3.4 | MS, RI |
| 7 | 2-n-Heptylfuran | 1190 | Green, fatty | 6 | MS, RI | |
| Alkanes | ||||||
| 1 | Undecane | 1098 | Unknown | 9 | 620 | MS, STD, RI |
| 2 | Dodecane | 1196 | Unknown | 9 | 110 | MS, STD, RI |
| 3 | Tridecane | 1295 | Unknown | 9 | MS, STD, RI | |
| Alkenes | ||||||
| 1 | α -Pinene | 933 | Pine, woody, herbal, fresh, fruity | 5 | 18 | MS, STD, RI |
| 2 | Camphene | 950 | Woody, herbal, camphoraceous | 5 | 130 | MS, RI |
| 3 | β-Terpinene | 975 | Terpenic, fatty | 5 | 130 | MS, RI |
| 4 | 3-Carene | 1009 | Citrus, sweet | 1 | 140 | MS, RI |
| 5 | p-Cymene | 1024 | Fruity, fresh, citrus, terpenic, floral, fragrant | 1 | 57 | MS, RI |
| 6 | D-Limonene | 1028 | Citrus, fresh, sweet | 1 | 38 | MS, STD, RI |
| 7 | γ-Terpinene | 1058 | Terpenic, citrus, herbal | 5 | 5 × 104 | MS, RI |
| 8 | α-Thujene2 | 1121 | Woody, herbal, green | 5 | MS, RI | |
| 9 | Alloocimene1 | 1128 | Floral, sweet, nut | 2 | 1.8 × 104 | MS, RI |
| 10 | β-Thujene | 953 | Unknown | MS, RI | ||
| 11 | 2,4-Dimethyl-1-decene | 1083 | Unknown | 9 | MS, RI | |
| 12 | β-Gurjunene | 1434 | Unknown | 9 | MS, RI | |
| Others | ||||||
| 1 | Dimethyl ether2,3,4 | 478 | Ethereal | 1 | 5 × 105 | MS, RI |
| 2 | 4-Ethenyl-1,2-dimethyl-benzene | 1088 | Unknown | 9 | MS, RI | |
| 3 | 4-Methyl-2-propylphenol1 | 1314 | Unknown | 9 | MS, RI | |
| 4 | α-Limonene-di-epoxide | 1031 | Citrus | 1 | MS, RI | |
| 5 | Unknown3 | 735 | ||||
| 6 | Unknown | 989 | ||||
| 7 | Unknown4 | 1028 | ||||
| 8 | Unknown | 1039 | ||||
| 9 | Unknown | 1079 | ||||
| 10 | Unknown | 1085 | ||||
| 11 | Unknown | 1332 | ||||
| 12 | Unknown | 1341 | ||||
An extended version that additionally includes the literature for the aroma descriptors and the odor thresholds is available in the Additional file 2: Table S7
aThe superscripted number represents newly formed volatiles during fermentation of oat milk (1), sunflower seed milk (2), pea milk (3), and faba milk (4)
bOdour groups: (1) fruity, citrus, sweet, malty, ethereal; (2) floral (3) buttery, fatty, waxy, creamy; (4) cheesy, sour; (5) nutty, woody, minty, toasted, turpentine, balsamic, camphoraceous; (6) green, grassy, bean-like, herbal; (7) earthy, mushroom; (8) pungent, spicy, sharp, phenolic; and (9) unknown odour