Table 1.
Volatile compounds produced by milk fermented with different proportions of L. delbrueckii subsp. bulgaricus IMAU20401 and S. thermophilus ND03.
| No. | Volatile Compound | Chemical Formula | RT (min) 1 | RI 2 | RI 3 | Method 4 | Ratio of L. delbrueckii subsp. bulgaricus to S. thermophiles (μg/L) | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1:1 | 1:10 | 1:50 | 1:100 | 1:1000 | 1:10,000 | |||||||
| Aldehyde Compounds | ||||||||||||
| 1 | Acetaldehyde | C2H4O | 1.26 | - | - | MS, STD | 6.86 | 7.11 | 7.77 | 11.15 | 14.33 | - |
| 2 | 3-Hydroxybutanal | C4H8O2 | 2.37 | 605 | - | MS | - | 1.33 | 2.39 | 1.16 | 6.96 | 5.46 |
| 3 | 3-Methylbutanal | C5H10O | 2.82 | 639 | 634 | MS, RI | - | 5.55 | 5.38 | 8.23 | 7.80 | 5.31 |
| 4 | Pentanal | C5H10O | 3.19 | 668 | 668 | MS, RI | - | - | 0.32 | 1.36 | 1.07 | - |
| 5 | (E)-2-Pentenal | C5H8O | 5.14 | 753 | 754 | MS, RI | - | 3.89 | - | 1.27 | 5.44 | - |
| 6 | Hexanal | C6H12O | 5.61 | 768 | 769 | MS, RI | - | 1.43 | 1.29 | 2.51 | 5.20 | 1.24 |
| 7 | (E)-2-Hexenal | C6H10O | 8.35 | 848 | 848 | MS, RI | 2.58 | 2.01 | 1.95 | 2.29 | - | - |
| 8 | Heptanal | C7H14O | 8.66 | 857 | 860 | MS, RI | 1.55 | 1.95 | 1.66 | 1.86 | 2.23 | - |
| 9 | Benzaldehyde | C7H6O | 11.77 | 932 | 933 | MS, RI | - | - | 0.31 | - | - | 3.05 |
| 10 | (E)-2-Heptenal | C7H12O | 12.28 | 953 | 953 | MS, RI | 3.82 | - | - | - | - | 0.23 |
| 11 | (E,E)-2,4-Heptadienal | C7H10O | 14.23 | 1006 | 1007 | MS, RI | - | - | 1.32 | - | - | - |
| 12 | (E)-2-Octenal | C8H14O | 15.82 | 1054 | 1055 | MS, RI | 1.26 | - | 0.32 | - | - | - |
| 13 | Nonanal | C9H18O | 16.85 | 1085 | 1086 | MS, RI | 2.92 | 0.25 | 0.31 | 0.30 | 0.86 | 1.22 |
| 14 | (E)-2-Nonenal | C9H16O | 19.03 | 1155 | 1157 | MS, RI | 3.93 | - | - | - | - | - |
| 15 | Decanal | C10H20O | 19.91 | 1184 | 1185 | MS, RI | 1.93 | - | - | - | 0.67 | - |
| 16 | (Z)-2-Decenal | C10H18O | 22.01 | 1257 | 1252 | MS, RI | 1.26 | - | - | - | - | - |
| Ketone Compounds | ||||||||||||
| 17 | 2,3-Butanedione | C4H6O2 | 2.25 | - | - | MS, STD | - | 1.06 | 2.11 | 2.33 | 2.13 | 5.88 |
| 18 | 2-Pentanone | C5H10O | 2.97 | 651 | 653 | MS, RI | - | - | 3.89 | 1.67 | 5.27 | 5.04 |
| 19 | 3-Methyl-2-butanone | C5H10O | 3.01 | 654 | 654 | MS, RI | 1.65 | 3.26 | 3.45 | 4.21 | 5.28 | 2.61 |
| 20 | 1-Hydroxy-2-propanone | C3H6O2 | 3.33 | 679 | 674 | MS, RI | - | 5.23 | - | - | - | - |
| 21 | Acetoin | C4H8O2 | 3.42 | 686 | - | MS, STD | - | 41.18 | 87.38 | 94.26 | 111.89 | 68.57 |
| 22 | 3-Methyl-(S)-2-butanol | C5H12O | 5.35 | 760 | - | MS | - | - | - | - | - | 4.30 |
| 23 | 2-Heptanone | C7H14O | 9.23 | 871 | 863 | MS, RI | 21.79 | 9.00 | 17.18 | 11.27 | 25.56 | 27.48 |
| 24 | 5-Methyl-3-heptanone | C8H16O | 12.43 | 957 | 962 | MS, RI | 1.31 | - | - | - | - | - |
| 25 | 2-Propyl-1-heptanol | C10H22O | 15.29 | 1033 | - | MS, RI | - | - | 0.25 | 0.18 | - | - |
| 26 | 2,5-Dimethyl-4-hydroxy-3(2H)-furanone | C6H8O3 | 16.08 | 1062 | 1060 | MS, RI | - | 0.53 | - | - | - | - |
| 27 | 2-Nonanone | C9H18O | 16.45 | 1071 | 1070 | MS, RI | 14.04 | 2.11 | 5.43 | 5.84 | 10.67 | 6.77 |
| 28 | 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one | C6H8O4 | 18.56 | 1140 | 1149 | MS, RI | - | 0.70 | - | - | - | - |
| 29 | 2-Undecanone | C11H22O | 22.48 | 1273 | 1273 | MS, RI | 1.84 | 0.85 | 1.07 | 0.62 | 1.39 | 1.03 |
| Acid Compounds | ||||||||||||
| 30 | Acetic acid | C2H4O2 | 2.56 | 619 | 622 | MS, RI, STD | 24.65 | 18.48 | 17.08 | 14.48 | 13.28 | 7.89 |
| 31 | 2-Oxopropanoic acid | C3H4O3 | 3.08 | 659 | - | MS | - | 1.70 | 1.34 | 1.18 | 1.67 | 1.79 |
| 32 | 2-Methylpropanoic acid | C4H8O2 | 5.12 | 752 | 753 | MS, RI | 2.88 | 5.68 | 6.64 | 5.32 | 4.85 | - |
| 33 | Butanoic acid | C4H8O2 | 6.30 | 793 | 793 | MS, RI | 16.83 | 12.07 | 11.40 | 11.14 | 4.02 | 0.62 |
| 34 | 3-Methylbutanoic acid | C5H10O2 | 8.22 | 845 | 845 | MS, RI | - | 3.35 | 8.33 | 6.79 | 5.04 | 4.09 |
| 35 | 2-Methylhexanoic acid | C7H14O2 | 8.93 | 863 | - | MS | - | 5.31 | 8.15 | 5.33 | 2.74 | 3.60 |
| 36 | 2-Methylbutanoic acid | C5H10O2 | 9.10 | 868 | - | MS | - | 7.16 | 12.42 | 10.24 | 9.29 | - |
| 37 | Pentanoic acid | C5H10O2 | 9.27 | 872 | 875 | MS, RI | - | 10.27 | 11.86 | 11.03 | 8.38 | - |
| 38 | Lactic acid | C3H6O3 | 10.82 | 914 | - | MS, STD | 6.67 | 5.41 | - | - | - | - |
| 39 | Hexanoic acid | C6H12O2 | 13.16 | 974 | 974 | MS, RI | 40.57 | 34.38 | 30.15 | 35.00 | 25.29 | 22.88 |
| 40 | 7-Oxo-Octanoic acid | C8H14O3 | 13.56 | 987 | - | MS | 3.94 | - | - | - | - | - |
| 41 | Heptanoic acid | C7H14O2 | 16.77 | 1083 | 1085 | MS, RI | 2.02 | 1.98 | 1.29 | 1.04 | - | - |
| 42 | Octanoic acid | C8H16O2 | 19.70 | 1177 | 1178 | MS, RI | 13.43 | 7.85 | 10.13 | 6.08 | 12.43 | 8.11 |
| 43 | Nonanoic acid | C9H18O2 | 21.08 | 1224 | 1226 | MS, RI | - | 2.99 | 1.85 | 1.69 | 1.78 | - |
| 44 | 2-Undecenoic acid | C11H20O2 | 22.31 | 1267 | - | MS | 0.73 | 0.67 | - | 0.35 | 1.11 | - |
| 45 | n-Decanoic acid | C10H20O2 | 24.54 | 1349 | 1349 | MS, RI | 2.01 | 1.74 | 3.66 | 2.40 | 1.07 | 3.79 |
| Ester Compounds | ||||||||||||
| 46 | Formic acid, hexyl ester | C7H14O2 | 8.94 | 864 | 870 | MS, RI | 1.44 | 1.89 | 1.97 | 2.65 | 1.87 | 2.29 |
| 47 | Heptanoic acid, 2-methyl-2-butyl ester | C12H24O2 | 14.10 | 1002 | - | MS | - | - | - | - | 0.89 | - |
| 48 | Sec-butyl nitrite | C4H9NO2 | 17.02 | 1090 | - | MS | - | 1.27 | - | - | - | - |
| 49 | Allyl 2-ethyl butyrate | C9H16O2 | 20.39 | 1200 | - | MS | - | - | - | 0.73 | 1.50 | - |
| 50 | Butanoic acid, 2-ethyl-,1,2,3-propanetriyl ester | C21H38O6 | 20.40 | 1200 | - | MS | - | - | 1.48 | 1.49 | 1.94 | - |
| 51 | Pentanoic acid, heptyl ester | C12H24O2 | 25.22 | 1375 | 1376 | MS, RI | - | 0.14 | - | 1.93 | - | - |
| Alcohol Compounds | ||||||||||||
| 52 | Cyclobutanol | C4H8O | 1.81 | - | - | MS | - | 4.22 | 5.49 | 6.49 | - | - |
| 53 | Trans-4-methylcyclohexanol | C7H14O | 3.18 | 667 | - | MS | 9.57 | - | - | - | - | - |
| 54 | 3-Methyl-2-butanol | C5H12O | 3.38 | 682 | 700 | MS, RI | 3.92 | 4.69 | 5.03 | 4.99 | - | - |
| 55 | 3-Methyl-3-buten-1-ol | C5H10O | 3.53 | 694 | 726 | MS, RI | - | - | - | - | 4.92 | - |
| 56 | 3-Methylbutanol | C5H12O | 4.54 | 732 | 732 | MS, RI | - | 23.12 | 20.55 | 14.89 | 15.86 | - |
| 57 | 2,2-Dimethyl-1-butanol | C6H14O | 4.83 | 742 | - | MS | - | - | - | - | 3.06 | - |
| 58 | Trans-1,2-cyclopentanediol | C5H10O2 | 5.49 | 765 | - | MS | - | - | - | - | 1.73 | 0.92 |
| 59 | 1-Propoxy-2-propanol | C6H14O2 | 5.67 | 771 | - | MS | - | - | - | - | - | 1.13 |
| 60 | 2-Methyl-3-pentanol | C6H14O | 6.67 | 804 | 805 | MS, RI | - | - | 2.09 | - | - | - |
| 61 | 1-Hexanol | C6H14O | 8.50 | 852 | 858 | MS, RI | 16.29 | 7.45 | 6.92 | 5.90 | 3.05 | 5.54 |
| 62 | 2-Methyl-3-pentanol | C8H18O | 9.40 | 876 | - | MS | - | 1.66 | 12.14 | - | - | - |
| 63 | 3-Methyl-2-hexanol | C7H16O | 10.30 | 900 | 906 | MS, RI | - | 0.24 | 1.96 | 2.96 | - | - |
| 64 | 5-Methyl-2-heptanol | C8H18O | 11.26 | 925 | - | MS | - | 0.71 | - | - | - | - |
| 65 | 2-Heptanol | C7H16O | 11.47 | 931 | 915 | MS, RI | - | 0.93 | - | - | - | 0.42 |
| 66 | 1-Heptanol | C7H16O | 13.17 | 976 | 974 | MS, RI | 12.49 | 1.86 | 2.92 | 3.10 | 8.37 | 4.38 |
| 67 | 1-Octen-3-ol | C8H16O | 13.26 | 979 | 979 | MS, RI | 2.15 | - | - | - | - | - |
| 68 | 3,5-Octadien-2-ol | C8H14O | 15.21 | 1036 | 1037 | MS, RI | 0.82 | - | - | - | - | - |
| 69 | 2-Nonen-1-ol | C9H18O | 15.79 | 1053 | - | MS | - | 3.46 | 1.93 | 1.42 | 2.33 | 2.58 |
| 70 | (E)-2-Octen-1-ol | C8H16O | 16.21 | 1066 | 1067 | MS, RI | 1.24 | - | - | - | - | - |
| 71 | 5-Ethyl-2-heptanol | C9H20O | 16.76 | 1082 | - | MS | - | - | - | - | 1.16 | - |
| 72 | 2-Nonanol | C9H20O | 17.24 | 1097 | 1098 | MS, RI | 1.14 | 1.59 | 2.38 | 3.98 | - | - |
| 73 | (E)-2-Nonen-1-ol | C9H18O | 19.32 | 1165 | 1171 | MS, RI | 1.26 | - | - | - | - | - |
| 74 | 1-Nonanol | C9H20O | 19.41 | 1168 | 1168 | MS, RI | 7.45 | 6.39 | 4.92 | 6.12 | 5.29 | 6.21 |
| 75 | (E)-2-Decen-1-ol | C10H20O | 22.23 | 1265 | - | MS | 1.64 | - | - | - | - | - |
| 76 | 2-Undecanol | C11H24O | 23.15 | 1297 | 1303 | MS, RI | - | 0.62 | - | 0.28 | - | - |
| Aromatic Hydrocarbons | ||||||||||||
| 77 | Toluene | C7H8 | 5.08 | 751 | 757 | MS, RI | - | 0.23 | 5.13 | 4.16 | 3.45 | - |
| 78 | 1,3,5-Cycloheptatriene | C7H8 | 5.38 | 761 | 765 | MS, RI | - | - | - | - | - | 0.91 |
| 79 | 2,4-Dimethylhexane | C8H18 | 6.15 | 787 | - | MS | 7.39 | 1.13 | - | - | - | - |
| 80 | 1-Octene | C8H16 | 6.17 | 788 | 791 | MS, RI | 1.35 | 0.98 | - | - | - | - |
| 81 | (E)-5-Methyl-2-hexene | C7H14 | 8.48 | 852 | - | MS | - | - | - | 1.52 | - | - |
| 82 | (Z)-2-Heptene | C7H14 | 9.17 | 870 | - | MS | - | 4.84 | - | - | - | - |
| 83 | Dodecane | C12H26 | 15.29 | 1038 | - | MS | - | - | - | 2.04 | - | 0.69 |
| 84 | 1-Nonyne | C9H16 | 15.78 | 1049 | - | MS | - | 1.91 | 1.89 | 2.17 | - | - |
| 85 | 2,4,6-Trimethyldecane | C13H28 | 17.91 | 1118 | 1121 | MS, RI | - | - | 1.54 | 1.62 | 1.65 | - |
| 86 | 4,6-Decadiene | C10H18 | 17.92 | 1119 | - | MS | 2.56 | - | - | - | - | - |
| 87 | 4-Ethylphenol | C8H10O | 19.12 | 1158 | 1161 | MS, RI | 0.64 | - | - | - | - | - |
| 88 | 2-Methylundecane | C12H26 | 19.33 | 1162 | 1164 | MS, RI | - | - | - | 1.66 | - | - |
| 89 | 2,3,5,8-Tetramethyldecane | C14H30 | 21.85 | 1251 | - | MS | - | 0.32 | 0.48 | 0.36 | 0.96 | - |
1 Retention time; 2 Retention index of unknown compounds on an HP-5MS column calculated against the gas chromatography-mass spectrometry (GC-MS) retention time of n-alkanes (C3–C25); 3 RI from database (http://webbook.nist.gov/chemistry); 4 RI, agreed with retention index in the literature; MS, compared with NIST 11 Mass Spectral Database; STD, agreed with the mass spectrum of standard chemical. ‘-’ = not detected.