3.1. Isolation of volatile compounds by distillation under reduced pressure (DRP) and continuous liquid-liquid extraction (LLE)
The volatile compounds of each bean (black bean, mung bean, soybean) extracted by DRP-LLE were analysed qualitatively, and the major volatile compounds were selected. A total of two aldehydes, seven alcohols, and one ketone were identified in black bean extracts (Table 1). The results of quantitative analysis of the volatile compounds in black bean extracts with various particle sizes and extraction temperatures are shown in Table 1. Bean samples have significantly different volatile components depending on the cultivation area and environment, but certain components exist in common (18). Among the 3 groups of volatile compounds, alcohols were detected the most, followed by aldehydes and ketones. Aldehydes extracted from black bean by DRP-LLE included hexanal and nonanal. Hexanal is characterized by a grassy and fatty odour, and nonanal had a floral and waxy odour (20). Compared with SDE method (26), a loss of volatiles was reduced in current DRP-LLE method.
Table 1
Concentrations of volatile compounds identified in black bean (Phaseolus vulgaris L.) extracts with DRP-LLE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 50°C | Distillation at 60°C | Distillation at 70°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Hexanal | 1069 | 1084 | MS, KI, Co | 1.012 ± 0.031a,A | 0.868 ± 0.027a,B | 0.214 ± 0.007a,B | 3.241 ± 0.098b,A | 0.927 ± 0.028a,B | 0.323 ± 0.010a,C | 3.877 ± 0.371b,A | 3.239 ± 0.098b,A | 0.829 ± 0.026b,B |
Nonanal | 1408 | 1395 | MS, KI, Co | 0.279 ± 0.008a,A | 0.207 ± 0.004a,B | 0.223 ± 0.006a,B | 0.376 ± 0.012b,A | 0.355 ± 0.011b,A | 0.206 ± 0.006a,B | 0.437 ± 0.053c,A | 0.467 ± 0.015c,A | 0.320 ± 0.009b,B |
Total aldehydes | | | | 1.291 ± 0.039 | 1.075 ± 0.030 | 0.437 ± 0.013 | 3.617 ± 0.110 | 1.283 ± 0.039 | 0.529 ± 0.016 | 3.475 ± 0.424 | 3.706 ± 0.113 | 1.149 ± 0.035 |
Alcohols | | | | | | | | | | | | |
2-Methyl-1-butanol | 1194 | 1208 | MS, KI, Co | 1.939 ± 0.060a,A | 2.238 ± 0.069a,B | 1.456 ± 0.044b,B | 5.659 ± 0.172b,A | 1.767 ± 0.053b,B | 1.437 ± 0.044a,C | 2.327 ± 0.081c,A | 2.318 ± 0.070a,A | 2.217 ± 0.064b,A |
1-Hexanol | 1365 | 1360 | MS, KI, Co | 0.876 ± 0.027a,A | 0.752 ± 0.021a,B | 0.514 ± 0.016a,C | 1.300 ± 0.039b,A | 1.087 ± 0.033b,B | 0.542 ± 0.016a,C | 0.777 ± 0.004c,AB | 0.805 ± 0.024c,A | 0.720 ± 0.021b,C |
1-Pentanol | 1230 | 1212 | MS, KI, Co | 6.741 ± 0.205a,A | 6.412 ± 0.198a,B | 4.256 ± 0.131a,C | 9.139 ± 0.279b,A | 6.688 ± 0.206ab,B | 4.210 ± 0.127a,C | 5.114 ± 0.050c,A | 5.264 ± 0.165c,A | 5.790 ± 0.179b,B |
3-Octanol | 1404 | 1394 | MS, KI, Co | 0.579 ± 0.018a,A | 0.410 ± 0.012a,B | 0.227 ± 0.007a,C | 0.619 ± 0.019b,A | 0.464 ± 0.014b,B | 0.209 ± 0.006a,C | 0.394 ± 0.015c,A | 0.400 ± 0.012a,A | 0.371 ± 0.010b,B |
1-Octen-3-ol | 1460 | 1445 | MS, KI, Co | 10.146 ± 0.309a,A | 9.189 ± 0.280a,B | 11.611 ± 0.354a,C | 12.023 ± 0.367b,A | 10.616 ± 0.326b,B | 8.151 ± 0.252b,C | 8.057 ± 0.409c,A | 8.249 ± 0.250c,A | 8.523 ± 0.262b,A |
Benzyl alcohol | 1900 | 1880 | MS, KI, Co | 1.210 ± 0.037a,A | 0.903 ± 0.029a,B | 0.855 ± 0.026a,B | 1.238 ± 0.038a,A | 1.725 ± 0.054b,B | 0.518 ± 0.016b,C | 0.612 ± 0.024b,A | 0.621 ± 0.019c,A | 0.770 ± 0.023c,B |
Phenethyl-alcohol | 1935 | 1929 | MS, KI, Co | 0.268 ± 0.009a,A | 0.367 ± 0.012a,B | 0.207 ± 0.007a,C | 0.354 ± 0.011b,A | 0.584 ± 0.015b,B | 0.117 ± 0.004b,C | 0.248 ± 0.008c,A | 0.251 ± 0.007c,A | 0.074 ± 0.002c,B |
Total alcohols | | | | 21.758 ± 0.665 | 20.271 ± 0.620 | 19.125 ± 0.585 | 30.332 ± 0.925 | 22.931 ± 0.701 | 15.183 ± 0.464 | 71.529 ± 0.530 | 17.906 ± 0.548 | 18.465 ± 0.561 |
Ketones | | | | | | | | | | | | |
γ-Hexalactone | 1702 | 1724 | MS, KI, Co | 0.095 ± 0.003a,A | 0.138 ± 0.005a,B | 0.033 ± 0.001a,C | 0.138 ± 0.004b,A | 0.212 ± 0.005b,B | 0.020 ± 0.001b,C | 0.059 ± 0.007c,A | 0.063 ± 0.002c,A | N.D. |
Total ketones | | | MS, KI, Co | 0.095 ± 0.003 | 0.138 ± 0.005 | 0.033 ± 0.001 | 0.138 ± 0.004 | 0.212 ± 0.005 | 0.020 ± 0.001 | 0.059 ± 0.007 | 0.063 ± 0.002 | N.D. |
Total volatiles | | | | 23.144 ± 0.707a,A | 21.483 ± 0.656a,B | 19.595 ± 0.599a,C | 34.087 ± 1.039b,A | 24.425 ± 0.746b,B | 15.733 ± 0.481b,C | 21.063 ± 0.923c,A | 21.675 ± 0.663a,A | 19.614 ± 0.596a,B |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detected |
At 50°C, the nonanal content was greater than the hexanal content. Alcohol compounds included 2-methyl-1-butanol, 1-pentanol, 1-hexanol, 3-octanol, 1-octen-3-ol, benzyl alcohol, and phenethyl alcohol. These alcohol compounds are characterized by sweet, oily, and floral odours. Among alcohol compounds, 1-octen-3-ol showed the highest concentration, and it had a mushroom-like and fatty odour (30). The ketone compound was γ-hexalactone, which had a waxy and creamy odour (31). However, at 70°C, γ-hexalactone was not detected. The sums of the peak area ratios of nine samples are presented in Table 1. The highest concentration of volatile compounds in black bean was extracted at 60°C with a particle size of 355–500 µm, while the lowest concentration of volatile compounds was extracted at 60°C with whole size. These results are consistent with the results of previous studies in which the smaller the coffee bean particles, the more soluble and volatile compounds were extracted (32).
A total of three aldehydes and seven alcohols were identified in mung bean extracts (Table 2), with alcohols being predominantly detected. The aldehyde compounds extracted from mung bean by DRP-LLE included octanal, nonanal, and benzaldehyde. According to the previous report, the major volatiles in mung beans are hexanol, benzyl alcohol, and γ-butyrolactone (22, 23).
Table 2
Concentrations of volatile compounds identified in mung bean (Vigna radiata L.) extracts with DRP-LLE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 50°C | Distillation at 60°C | Distillation at 70°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Octanal | 1282 | 1264 | MS, KI, Co | 0.020 ± 0.001a,A | N.D. | 0.016 ± 0.002a,B | 0.006 ± 0.001b,A | 0.015 ± 0.001a,BC | 0.015 ± 0.001ab,BC | N.D. | 0.019 ± 0.002b,A | 0.014 ± 0.002b,B |
Nonanal | 1401 | 1395 | MS, KI, Co | 0.418 ± 0.025a,A | 0.123 ± 0.007a,B | 0.255 ± 0.028a,C | 0.361 ± 0.045ab,AB | 0.283 ± 0.014b,C | 0.302 ± 0.032ab,AC | 0.163 ± 0.079c,A | 0.279 ± 0.023b,B | 0.260 ± 0.028a,B |
Benzaldehyde | 1539 | 1527 | MS, KI, Co | 0.292 ± 0.018a,A | 0.335 ± 0.017a,A | 0.219 ± 0.024a,A | 0.252 ± 0.031a,A | 0.694 ± 0.035b,B | 0.215 ± 0.023a,A | 0.428 ± 0.108ab,AB | 0.256 ± 0.022a,A | 4.666 ± 0.122b,C |
Total aldehydes | | | | 0.507 ± 0.031 | 0.525 ± 0.026 | 0.324 ± 0.035 | 0.406 ± 0.051 | 0.990 ± 0.050 | 0.319 ± 0.034 | 0.577 ± 0.144 | 0.429 ± 0.036 | 4.501 ± 0.484 |
Alcohols | | | | | | | | | | | | |
2-Methyl-1-butanol | 1205 | 1208 | MS, KI, Co | 4.529 ± 0.273a,A | 4.957 ± 0.253a,A | 1.242 ± 0.134a,B | 3.668 ± 0.453b,A | 6.140 ± 0.313b,B | 1.254 ± 0.135a,C | 1.138 ± 0.065c,A | 4.037 ± 0.333c,A | 0.842 ± 0.090a,A |
1-Pentanol | 1235 | 1212 | MS, KI, Co | 0.433 ± 0.026a,A | 0.447 ± 0.023a,A | 0.223 ± 0.025a,B | 0.322 ± 0.040b,A | 0.615 ± 0.031b,B | 0.247 ± 0.027a,C | 0.217 ± 0.097c,A | 0.343 ± 0.032c,A | 0.232 ± 0.025a,A |
1-Hexanol | 1377 | 1360 | MS, KI, Co | 1.467 ± 0.088a,A | 1.084 ± 0.055a,B | 0.678 ± 0.073a,C | 1.049 ± 0.129b,A | 1.644 ± 0.084b,B | 0.680 ± 0.073a,C | 0.250 ± 0.030c,A | 0.873 ± 0.073c,B | 0.483 ± 0.052b,C |
1-Octanol | 1577 | 1563 | MS, KI, Co | 0.195 ± 0.012a,A | 0.190 ± 0.009a,A | 0.089 ± 0.010a,B | 0.148 ± 0.019b,A | 0.281 ± 0.014b,B | 0.089 ± 0.010a,C | 0.149 ± 0.037b,A | 0.150 ± 0.013c,A | 0.090 ± 0.010a,B |
1-Nonanol | 1714 | 1724 | MS, KI, Co | 0.432 ± 0.026a,A | 0.384 ± 0.020a,B | 0.173 ± 0.019a,C | 0.224 ± 0.028b,A | 0.594 ± 0.030b,B | 0.172 ± 0.019a,C | 0.224 ± 0.0450b,A | 0.293 ± 0.025c,B | 0.159 ± 0.017a,C |
Benzyl alcohol | 1900 | 1880 | MS, KI, Co | 1.120 ± 0.067a,A | 2.168 ± 0.111a,B | 0.966 ± 0.104ab,AC | 0.466 ± 0.057b,A | 3.170 ± 0.161b,B | 1.114 ± 0.120b,C | 0.299 ± 0.097b,A | 1.112 ± 0.093c,B | 0.798 ± 0.086a,C |
Phenethyl alcohol | 1930 | 1929 | MS, KI, Co | 1.010 ± 0.061a,A | 2.399 ± 0.122a,B | 1.150 ± 0.124a,A | 0.199 ± 0.025b,A | 2.604 ± 0.135b,B | 1.148 ± 0.124a,C | N.D. | 0.835 ± 0.070c,A | 0.438 ± 0.048b,B |
Total alcohols | | | | 9.184 ± 0.553 | 11.628 ± 0.592 | 4.527 ± 0.487 | 6.076 ± 0.750 | 15.048 ± 0.768 | 4.705 ± 0.507 | 2.277 ± 0.096 | 7.643 ± 0.638 | 3.041 ± 0.328 |
Total volatiles | | | | 9.915 ± 0.597a,A | 12.093 ± 0.616a,B | 5.017 ± 0.540a,C | 6.695 ± 0.827b,A | 16.039 ± 0.818b,B | 5.237 ± 0.564a,C | 2.869 ± 0.242c,A | 8.201 ± 0.684c,B | 7.712 ± 0.831b,BC |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detected |
Octanal is characterized by a fatty odour and benzaldehyde had a bitter almond odour (28). Among the aldehyde compounds, benzaldehyde was usually detected more often than the other compounds. Octanal was not detected at 50°C for the 500–700 µm size and at 70°C for the 355–500 µm size. The alcohol compounds included 2-methyl-1-butanol, 1-pentanol, 1-hexanol, 1-octanol, 1-nonanol, benzyl alcohol, and phenethyl alcohol. Among the alcohol compounds, 2-methyl-1-butanol was predominant. Phenethyl alcohol was not detected at 70°C for the 355–500 µm size. The highest concentration of volatile compounds in mung bean was extracted at 60°C with a particle size of 500–710 µm, while the lowest concentration of volatile compounds was extracted at 70°C with a particle size of 355–500 µm. This shows the same tendency as the result that when fine particles (355–510 µm) are used in the espresso method, the penetration rate may be slow because the gaps between the ground coffee powder are small and the porosity is low (33). Also, a previous study has suggested that this is because the cellular structure of coffee beans opens up, allowing higher levels of residual levels of volatile compounds to be released (34).
A total of three aldehydes and seven alcohols were identified in soybean extracts (Table 3), with alcohols being predominantly detected. The aldehyde compounds extracted from soybean by DRP-LLE included hexanal, nonanal, and benzaldehyde. Among these aldehyde compounds, hexanal was usually detected more than the other compounds. Benzaldehyde was not detected at 70°C for whole size. The alcohol compounds detected included 2-methyl-1-butanol, 1-hexanol, cis-3-hexen-1-ol, 3-octanol, 1-nonanol, benzyl alcohol, and phenethyl alcohol. Among the alcohol compounds, 1-hexanol was usually detected more than the other compounds. 1-Nonanol was not detected at 50°C for the 500–710 µm size. The sums of the peak area ratios of nine samples are presented in Table 3. The highest concentration of volatile compounds in soybean was extracted at 50°C with a particle size of 355–500 µm. However, the lowest concentration of volatile compounds in soybean was extracted at 60°C with whole size. This result is similar to the tendency for black bean samples.
Table 3
Concentrations of volatile compounds identified in soybean (Glycine max L.) extracts with DRP-LLE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 50°C | Distillation at 60°C | Distillation at 70°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | 355–500 ㎛ | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Hexanal | 1074 | 1084 | MS, KI, Co | 2.127 ± 0.065a,A | 1.004 ± 0.030a,B | 0.289 ± 0.009a,C | 1.255 ± 0.037b,A | 1.495 ± 0.044b,B | 0.148 ± 0.004b,C | 1.147 ± 0.035c,A | 2.003 ± 0.062c,B | 0.202 ± 0.006b,C |
Nonanal | 1412 | 1395 | MS, KI, Co | 0.414 ± 0.012a,A | 0.190 ± 0.006a,B | 0.218 ± 0.007a,C | 0.214 ± 0.007b,A | 0.204 ± 0.006bc,AB | 0.233 ± 0.007b,C | 0.445 ± 0.013c,A | 0.191 ± 0.006ab,BC | 0.188 ± 0.005c,C |
Benzaldehyde | 1521 | 1527 | MS, KI, Co | 0.678 ± 0.020a,A | 0.646 ± 0.020a,A | 0.201 ± 0.006a,B | 0.599 ± 0.019b,A | 1.271 ± 0.040b,B | 0.144 ± 0.004b,C | 0.606 ± 0.018b,A | 0.881 ± 0.026c,B | N.D. |
Total aldehydes | | | | 3.219 ± 0.098 | 1.840 ± 0.055 | 0.708 ± 0.022 | 2.067 ± 0.063 | 2.969 ± 0.090 | 0.525 ± 0.016 | 2.199 ± 0.067 | 3.075 ± 0.093 | 0.390 ± 0.011 |
Alcohols | | | | | | | | | | | | |
2-Methyl-1-butanol | 1194 | 1208 | MS, KI, Co | 5.259 ± 0.161a,A | 1.963 ± 0.060a,B | 1.361 ± 0.042a,C | 0.982 ± 0.030b,A | 1.716 ± 0.053b,B | 0.512 ± 0.016b,C | 1.183 ± 0.036c,A | 1.020 ± 0.031c,B | 1.098 ± 0.034c,AB |
1-Hexanol | 1368 | 1360 | MS, KI, Co | 4.112 ± 0.127a,A | 3.000 ± 0.092a,B | 1.606 ± 0.049a,C | 3.266 ± 0.100b,A | 4.612 ± 0.141b,B | 0.982 ± 0.030b,C | 4.070 ± 0.125a,A | 3.503 ± 0.106c,B | 1.069 ± 0.033b,C |
cis-3-Hexen-1-ol | 1401 | 1391 | MS, KI, Co | 0.778 ± 0.024a,A | 0.251 ± 0.008a,B | 0.109 ± 0.003a,C | 0.398 ± 0.012b,A | 0.333 ± 0.011ab,AB | 0.026 ± 0.001a,C | 0.585 ± 0.018c,A | 0.299 ± 0.010ab,B | 5.772 ± 0.176b,C |
3-Octanol | 1417 | 1394 | MS, KI, Co | 0.718 ± 0.022a,A | 0.653 ± 0.020a,B | 0.479 ± 0.015a,C | 0.400 ± 0.012b,A | 0.845 ± 0.026b,B | 0.334 ± 0.010b,C | 0.471 ± 0.014c,A | 0.538 ± 0.016c,B | 0.319 ± 0.009b,C |
1-Nonanol | 1672 | 1666 | MS, KI, Co | 0.255 ± 0.008a,A | N.D. | 0.106 ± 0.003a,C | 0.138 ± 0.004b,A | 0.246 ± 0.007a,C | 0.175 ± 0.005b,B | 0.175 ± 0.005c,A | 0.174 ± 0.005b,A | 0.061 ± 0.002c,C |
Benzyl alcohol | 1891 | 1880 | MS, KI, Co | 1.529 ± 0.047a,A | 1.052 ± 0.033a,B | 0.556 ± 0.017a,C | 1.141 ± 0.034b,A | 1.508 ± 0.045b,B | 0.678 ± 0.021b,C | 1.062 ± 0.033c,A | 0.741 ± 0.023c,B | 0.493 ± 0.015c,C |
Phenethyl-alcohol | 1930 | 1929 | MS, KI, Co | 0.239 ± 0.007a,A | 0.229 ± 0.007a,B | 0.053 ± 0.002a,C | 0.189 ± 0.006b,A | 0.288 ± 0.009b,B | 0.041 ± 0.001b,C | 0.118 ± 0.004c,A | 0.123 ± 0.004c,A | 0.043 ± 0.001b,B |
Total alcohols | | | | 12.890 ± 0.394 | 7.148 ± 0.219 | 4.269 ± 0.130 | 6.514 ± 0.199 | 9.547 ± 0.291 | 2.747 ± 0.084 | 7.665 ± 0.234 | 6.397 ± 0.195 | 8.853 ± 0.271 |
Total volatiles | | | | 16.109 ± 0.492a,A | 8.988 ± 0.275ab,B | 4.977 ± 0.152a,C | 8.581 ± 0.261b,A | 12.517 ± 0.381c,B | 3.271 ± 0.099b,C | 9.864 ± 0.301c,A | 9.472 ± 0.289b,AB | 9.243 ± 0.283c,B |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detected |
3.2. Isolation of volatile compounds by HWE and HS-SPME
A total of three aldehydes, five alcohols, and two ketones were identified in black bean extracts by HWE (Table 4). The 10 major volatile compounds were selected and analysed. Among the three groups of volatile compounds, alcohols were detected the most, followed by aldehydes and ketones. Aldehyde compounds detected by HS-SPME in black bean extracts included hexanal, nonanal, and benzaldehyde. Among the aldehyde compounds, hexanal was detected more often than the other compounds. The alcohol compounds included 1-hexanol, 3-octanol, 1-octen-3-ol, benzyl alcohol, and phenethyl alcohol, of which 1-octen-3-ol was predominantly detected. The ketone compounds detected were 2-heptanone and 3-octanone. 2-Heptanone had a soapy odour while 3-octanone had a herbaceous and buttery odour (27, 35). The sums of the peak area ratios of nine samples are presented in Table 4. The lower the incubation temperature, the higher the concentration of volatile compounds.
Table 4
Concentrations of volatile compounds identified in black bean (Phaseolus vulgaris L.) extracts with HWE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 70°C | Distillation at 80°C | Distillation at 90°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Hexanal | 1074 | 1084 | MS, KI, Co | 2.173 ± 0.003a,A | 4.292 ± 0.004a,B | 0.461 ± 0.003a,C | 1.125 ± 0.003b,A | 2.354 ± 0.001b,B | 0.656 ± 0.003b,C | 0.659 ± 0.002c,A | 1.119 ± 0.002c,B | 0.314 ± 0.001c,C |
Nonanal | 1412 | 1395 | MS, KI, Co | 0.223 ± 0.001a,A | 0.308 ± 0.001a,B | 0.036 ± 0.001a,C | 0.152 ± 0.001b,A | 0.198 ± 0.002b,B | 0.366 ± 0.001b,C | 0.102 ± 0.002c,A | 0.152 ± 0.001c,B | 0.078 ± 0.002c,C |
Benzaldehyde | 1521 | 1527 | MS, KI, Co | 1.633 ± 0.006a,A | 1.937 ± 0.003a,B | 0.375 ± 0.003a,C | 1.291 ± 0.004b,A | 1.749 ± 0.002b,B | 0.494 ± 0.002b,C | 1.171 ± 0.008c,A | 1.271 ± 0.004c,B | 0.687 ± 0.002c,C |
Total aldehydes | | | | 4.029 ± 0.006 | 6.538 ± 0.004 | 0.871 ± 0.005 | 2.569 ± 0.003 | 4.298 ± 0.002 | 1.186 ± 0.002 | 1.932 ± 0.001 | 2.543 ± 0.005 | 1.076 ± 0.005 |
Alcohols | | | | | | | | | | | | |
1-Hexanol | 1363 | 1360 | MS, KI, Co | 1.583 ± 0.001a,A | 1.784 ± 0.002a,B | 0.545 ± 0.004a,C | 0.459 ± 0.001b,A | 0.998 ± 0.003b,B | 0.416 ± 0.005b,C | 0.485 ± 0.002c,A | 0.458 ± 0.005c,B | 0.194 ± 0.004c,C |
3-Octanol | 1400 | 1394 | MS, KI, Co | 0.052 ± 0.003a,A | 0.111 ± 0.002a,B | 0.106 ± 0.001a,C | 0.041 ± 0.002b,A | 0.077 ± 0.004b,B | 0.076 ± 0.004b,B | 0.019 ± 0.001c,A | 0.041 ± 0.003c,B | 0.044 ± 0.002c,C |
1-Octen-3-ol | 1458 | 1445 | MS, KI, Co | 7.966 ± 0.002a,A | 12.145 ± 0.008a,B | 7.025 ± 0.010a,C | 3.781 ± 0.002b,A | 7.308 ± 0.004b,B | 5.664 ± 0.008b,C | 2.713 ± 0.004c,A | 3.573 ± 0.003c,B | 3.321 ± 0.004c,C |
Benzyl alcohol | 1886 | 1880 | MS, KI, Co | 0.498 ± 0.004a,A | 0.171 ± 0.003a,B | 0.016 ± 0.001a,C | 0.106 ± 0.004b,A | 0.149 ± 0.001b,B | 0.012 ± 0.001b,C | 0.142 ± 0.003c,A | 0.110 ± 0.004c,B | 0.016 ± 0.002c,C |
Phenethyl-alcohol | 1912 | 1929 | MS, KI, Co | 0.014 ± 0.004a,A | 0.019 ± 0.001a,B | 0.120 ± 0.002a,C | 0.015 ± 0.004b,A | 0.021 ± 0.001b,B | 0.076 ± 0.002b,C | 0.010 ± 0.002c,A | 0.016 ± 0.004c,B | 0.067 ± 0.001c,C |
Total alcohols | | | | 10.113 ± 0.003 | 14.226 ± 0.004 | 7.813 ± 0.007 | 4.401 ± 0.003 | 8.552 ± 0.005 | 6.245 ± 0.009 | 3.368 ± 0.007 | 4.198 ± 0.003 | 3.643 ± 0.005 |
Ketones | | | | | | | | | | | | |
2-Heptanone | 1193 | 1189 | MS, KI, Co | 0.284 ± 0.001a,A | 0.474 ± 0.001a,B | 0.024 ± 0.001a,C | 0.228 ± 0.002b,A | 0.363 ± 0.006b,B | 0.085 ± 0.002b,C | 0.130 ± 0.001c,A | 0.226 ± 0.003c,B | 0.044 ± 0.007c,C |
3-Octanone | 1266 | 1261 | MS, KI, Co | 0.207 ± 0.001a,A | 0.667 ± 0.003a,B | 0.087 ± 0.002a,C | 0.131 ± 0.003b,A | 0.327 ± 0.001b,B | 0.052 ± 0.004b,C | 0.070 ± 0.003c,A | 0.128 ± 0.001c,B | 0.024 ± 0.002c,C |
Total ketones | | | | 0.493 ± 0.001 | 1.141 ± 0.001 | 0.111 ± 0.001 | 0.358 ± 0.001 | 0.689 ± 0.008 | 0.137 ± 0.003 | 0.199 ± 0.003 | 0.355 ± 0.001 | 0.068 ± 0.009 |
Total volatiles | | | | 14.632 ± 0.004a,A | 21.904 ± 0.004a,B | 8.795 ± 0.001a,C | 7.328 ± 0.006b,A | 13.539 ± 0.004b,B | 7.568 ± 0.006b,C | 5.503 ± 0.004c,A | 7.095 ± 0.004c,B | 4.786 ± 0.004c,C |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detected |
A total of three aldehydes, six alcohols, and one ketone were identified in mung bean extracts (Table 5). Among the three groups of volatile compounds, alcohols were detected the most, followed by aldehydes and ketones. The aldehyde compounds detected in mung bean extracts by HS-SPME included hexanal, nonanal, and benzaldehyde, with benzaldehyde being detected more than the other compounds. The alcohol compounds included 1-hexanol, cis-3-hexen-1-ol, 1-octen-3-ol, 1-octanol, benzyl alcohol, and phenethyl alcohol, with 1-hexanol being detected in the highest concentration. The ketone compound detected was 2-heptanone. The sums of the peak area ratios of nine samples are presented in Table 5. The lower incubation temperature, the higher the concentration of volatile compounds, similar to the tendency for black bean.
Table 5
Concentrations of volatile compounds identified in mung bean (Vigna radiata L.) extracts with HWE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 70°C | Distillation at 80°C | Distillation at 90°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Hexanal | 1092 | 1084 | MS, KI, Co | 1.876 ± 0.008a,A | 4.746 ± 0.001a,B | 0.597 ± 0.001a,C | 0.472 ± 0.001b,A | 1.918 ± 0.009b,B | 0.406 ± 0.001b,A | 0.437 ± 0.001c,A | 1.091 ± 0.020c,B | 0.383 ± 0.002c,A |
Nonanal | 1404 | 1395 | MS, KI, Co | 0.712 ± 0.001a,A | 2.189 ± 0.003a,B | 0.471 ± 0.002a,C | 0.222 ± 0.001b,A | 1.671 ± 0.065b,B | 0.491 ± 0.002a,C | 0.153 ± 0.002c,A | 1.822 ± 0.080c,B | 0.245 ± 0.001b,C |
Benzaldehyde | 1540 | 1527 | MS, KI, Co | 3.416 ± 0.004a,A | 4.548 ± 0.003a,B | 1.706 ± 0.002a,C | 1.196 ± 0.003b,A | 3.159 ± 0.055b,B | 2.155 ± 0.001b,C | 1.062 ± 0.002c,A | 3.017 ± 0.094c,B | 4.834 ± 0.001c,C |
Total aldehydes | | | | 6.003 ± 0.011 | 11.483 ± 0.001 | 2.773 ± 0.002 | 1.891 ± 0.006 | 6.747 ± 0.085 | 3.051 ± 0.001 | 1.650 ± 0.004 | 5.930 ± 0.038 | 5.461 ± 0.002 |
Alcohols | | | | | | | | | | | | |
1-Hexanol | 1363 | 1360 | MS, KI, Co | 3.723 ± 0.005a,A | 2.383 ± 0.001a,B | 3.298 ± 0.001a,C | 0.817 ± 0.003b,A | 0.976 ± 0.034b,B | 2.034 ± 0.005b,C | 0.554 ± 0.005c,A | 0.547 ± 0.003c,A | 0.913 ± 0.003c,B |
cis-3-Hexen-1-ol | 1393 | 1391 | MS, KI, Co | 0.932 ± 0.001a,A | 0.435 ± 0.001a,B | 0.346 ± 0.001a,C | 0.182 ± 0.002b,A | 0.186 ± 0.003b,B | 0.246 ± 0.001b,C | 0.145 ± 0.002c,A | 0.102 ± 0.004c,B | 0.081 ± 0.001c,C |
1-Octen-3-ol | 1459 | 1445 | MS, KI, Co | 0.910 ± 0.002a,A | 2.234 ± 0.002a,B | 2.092 ± 0.006a,C | 0.284 ± 0.004b,A | 1.095 ± 0.010b,B | 1.703 ± 0.002b,C | 0.227 ± 0.002c,A | 0.661 ± 0.033c,B | 0.984 ± 0.001c,C |
1-Octanol | 1569 | 1563 | MS, KI, Co | 0.747 ± 0.001a,A | 1.507 ± 0.001a,B | 0.522 ± 0.001a,C | 0.214 ± 0.002b,A | 1.107 ± 0.045b,B | 0.457 ± 0.002b,C | 0.186 ± 0.003b,A | 0.788 ± 0.020c,B | 0.635 ± 0.002c,C |
Benzyl alcohol | 1887 | 1880 | MS, KI, Co | 1.683 ± 0.003a,A | 1.224 ± 0.005a,B | 1.136 ± 0.001a,C | 0.503 ± 0.001b,A | 0.787 ± 0.049b,B | 1.245 ± 0.001b,C | 0.396 ± 0.004c,A | 0.619 ± 0.013c,B | 1.620 ± 0.001c,C |
Phenethyl-alcohol | 1913 | 1929 | MS, KI, Co | 0.232 ± 0.001a,A | 0.162 ± 0.001a,B | 2.073 ± 0.006a,C | 0.084 ± 0.005b,A | 0.124 ± 0.006b,B | 2.132 ± 0.006b,C | 0.105 ± 0.002c,A | 0.122 ± 0.012b,B | 0.747 ± 0.002c,C |
Total alcohols | | | | 8.227 ± 0.004 | 7.944 ± 0.006 | 9.468 ± 0.008 | 2.083 ± 0.009 | 4.275 ± 0.041 | 7.816 ± 0.010 | 1.613 ± 0.001 | 2.839 ± 0.054 | 4.962 ± 0.004 |
Ketones | | | | | | | | | | | | |
2-Heptanone | 1193 | 1189 | MS, KI, Co | 0.323 ± 0.004a,A | 2.425 ± 0.002a,B | 0.987 ± 0.001a,C | 0.147 ± 0.001b,A | 1.134 ± 0.050b,B | 0.554 ± 0.001b,C | 0.137 ± 0.001b,A | 0.764 ± 0.012c,B | 0.192 ± 0.001c,C |
Total ketones | | | | 0.323 ± 0.004a,A | 2.425 ± 0.002a,B | 0.987 ± 0.001a,C | 0.147 ± 0.001b,A | 1.134 ± 0.050b,B | 0.554 ± 0.001b,C | 0.137 ± 0.001b,A | 0.764 ± 0.012c,B | 0.192 ± 0.001c,C |
Total volatiles | | | | 14.554 ± 0.003a,A | 21.851 ± 0.009a,B | 13.228 ± 0.009a,C | 4.121 ± 0.006b,A | 12.156 ± 0.013b,B | 11.421 ± 0.010b,C | 3.400 ± 0.004c,A | 9.533 ± 0.009c,B | 10.616 ± 0.005c,C |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detected |
A total of two aldehydes and eight alcohols were identified in soybean (Table 6). Among the two groups of volatile compounds, alcohols were detected the most, followed by aldehydes. The aldehyde compounds detected by HS-SPME included hexanal and benzaldehyde. Among aldehyde compounds, hexanal was detected more than benzaldehyde. The alcohol compounds included 2-methyl-1-butanol, 1-hexanol, cis-3-hexen-1-ol, 3-octanol, 1-octen-3-ol, 1-octanol, benzyl alcohol and phenethyl alcohol, with 1-octen-3-ol being detected in the highest concentration. The sums of the peak area ratios of nine samples are presented in Table 6. The lower the incubation temperature, the higher the concentration of volatile compounds, similar to the tendency for black bean and mung bean. Previous studies have demonstrated that HS-SPME at a low incubation temperature is the most efficient method when analyzing the volatile compounds of soymilk made from soy beans (36).
Table 6
Concentrations of volatile compounds identified in soybean (Glycine max L.) extracts with HWE
Compounds | KI | KI (Ref.) | Identification | Peak area ratio1) |
Distillation at 70°C | Distillation at 80°C | Distillation at 90°C |
355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size | 355–500 ㎛ | 500–710 ㎛ | Whole size |
Aldehydes | | | | | | | | | | | | |
Hexanal | 1092 | 1084 | MS, KI, Co | 3.583 ± 0.002a,A | 2.177 ± 0.001a,B | 1.267 ± 0.001a,C | 1.533 ± 0.001b,A | 1.366 ± 0.007b,B | 0.144 ± 0.000b,C | 0.845 ± 0.002c,A | 0.778 ± 0.016c,B | 0.133 ± 0.003c,C |
Benzaldehyde | 1540 | 1527 | MS, KI, Co | 1.863 ± 0.024a,A | 0.847 ± 0.002a,B | 0.979 ± 0.001a,C | 1.550 ± 0.014b,A | 0.658 ± 0.030b,B | 0.340 ± 0.001b,C | 1.162 ± 0.004c,A | 0.393 ± 0.003c,B | 0.531 ± 0.002c,C |
Total aldehydes | | | | 5.446 ± 0.022 | 3.023 ± 0.003 | 2.246 ± 0.001 | 3.083 ± 0.013 | 2.025 ± 0.010 | 0.484 ± 0.002 | 2.008 ± 0.003 | 1.170 ± 0.016 | 0.665 ± 0.004 |
Alcohols | | | | | | | | | | | | |
2-Methyl-1-butanol | 1215 | 1208 | MS, KI, Co | 0.033 ± 0.001a,A | 0.021 ± 0.002a,B | 0.066 ± 0.001a,C | 0.020 ± 0.001b,A | 0.012 ± 0.000b,B | 0.071 ± 0.001b,C | 0.011 ± 0.004c,A | 0.007 ± 0.002c,B | 0.052 ± 0.002c,C |
1-Hexanol | 1363 | 1360 | MS, KI, Co | 1.975 ± 0.007a,A | 0.233 ± 0.003a,B | 1.148 ± 0.001a,C | 0.989 ± 0.002b,A | 0.146 ± 0.002b,B | 0.926 ± 0.004b,C | 0.531 ± 0.001c,A | 0.110 ± 0.002c,B | 0.588 ± 0.004c,C |
cis-3-Hexen-1-ol | 1393 | 1391 | MS, KI, Co | 0.039 ± 0.001a,A | 0.011 ± 0.003a,B | 0.083 ± 0.001a,C | 0.019 ± 0.001b,A | 0.007 ± 0.001b,B | 0.070 ± 0.002b,C | 0.009 ± 0.000c,A | 0.003 ± 0.000c,B | 0.048 ± 0.002c,C |
3-Octanol | 1401 | 1394 | MS, KI, Co | 0.042 ± 0.001a,A | 0.022 ± 0.001a,B | 0.297 ± 0.001a,C | 0.045 ± 0.003b,A | 0.028 ± 0.001b,B | 0.249 ± 0.001b,C | 0.032 ± 0.001c,A | 0.016 ± 0.001c,B | 0.189 ± 0.003c,C |
1-Octen-3-ol | 1459 | 1445 | MS, KI, Co | 4.225 ± 0.035a,A | 2.241 ± 0.010a,B | 8.894 ± 0.002a,C | 2.062 ± 0.015b,A | 1.305 ± 0.017b,B | 5.835 ± 0.007b,C | 1.398 ± 0.005c,A | 0.767 ± 0.003c,B | 4.213 ± 0.007c,C |
1-Octanol | 1569 | 1563 | MS, KI, Co | 0.249 ± 0.007a,A | 0.274 ± 0.002a,B | 0.107 ± 0.002a,C | 0.158 ± 0.002b,A | 0.174 ± 0.004b,B | 0.060 ± 0.003b,C | 0.109 ± 0.001c,A | 0.093 ± 0.002c,B | 0.050 ± 0.001c,C |
Benzyl alcohol | 1887 | 1880 | MS, KI, Co | 0.438 ± 0.003a,A | 0.049 ± 0.002a,B | 0.036 ± 0.001a,C | 0.423 ± 0.022b,A | 0.028 ± 0.001b,B | 0.044 ± 0.002b,C | 0.269 ± 0.002c,A | 0.026 ± 0.002c,B | 0.046 ± 0.001c,C |
Phenethyl-alcohol | 1913 | 1895 | MS, KI, Co | 0.035 ± 0.002a,A | 0.010 ± 0.001a,B | 0.057 ± 0.001a,C | 0.039 ± 0.010b,A | 0.008 ± 0.003b,B | 0.098 ± 0.003b,C | 0.022 ± 0.002c,A | 0.007 ± 0.000c,B | 0.091 ± 0.004c,C |
Total alcohols | | | | 7.034 ± 0.021 | 2.838 ± 0.009 | 10.687 ± 0.002 | 3.753 ± 0.006 | 1.695 ± 0.014 | 7.354 ± 0.007 | 2.381 ± 0.005 | 1.021 ± 0.003 | 5.276 ± 0.001 |
Total volatiles | | | | 12.481 ± 0.005a,A | 5.883 ± 0.007a,B | 12.933 ± 0.003a,C | 6.836 ± 0.007b,A | 3.732 ± 0.005b,B | 7.838 ± 0.006b,C | 4.388 ± 0.002c,A | 2.197 ± 0.011c,B | 5.941 ± 0.005c,C |
1) All concentration values are presented as mean ± standard deviation. 2) MS, identification of mass spectrum with reference to the NIST mass spectrum library, 3) Kovats retention index on DB-WAX; KI (Ref), Retention index on DB-WAX in the NIST database. Mean values with different letters (a, b, c – extraction temperature/A, B, C – particle size) in the same horizontal line indicate significant differences according to Duncan’s test (p < 0.05). N.D.: not detect |
Among the total volatile compounds of extracts of various beans detected by DRP-LLE, black bean showed the highest concentration of volatile compounds, followed by soybean and mung bean. However, mung bean showed the highest concentration of volatile compounds in HS-SPME. The total volatile compound contents of black bean and soybean extracts detected by DRP-LLE were more than those detected by HS-SPME. However, the volatile compound content in mung bean extracts detected by DRP-LLE was less than that detected by HS-SPME. In conclusion, DRP-LLE for black beans and soybeans and HWE for mung beans were the highest concentration of volatile compounds. The difference in the concentration of volatile compounds detected in different species may be due to differences in the internal structure of beans and the distribution of compound components (34).