3.1. Descriptive Sensory Analysis
Twenty-five of the attributes previously reported for green tea [
7] were detected and evaluated for the six samples and five brews tested in this study. It is important to view these teas in terms of the description of those attributes as that can help in understanding the sensory profile of the teas. Those attributes were green, asparagus, celery, green herb-like, parsley, spinach, brown, ashy/sooty, burnt/scorched, tobacco, citrus, floral/perfumy, fruity, grain, medicinal, musty/new leather, nutty, seaweed, straw-like, sweet aromatics, bitter, astringent, and tooth-etch. Some attributes were similar to those found in three other Korean green teas [
26] which were bitter, floral, cut grass, roasted grain, dried straw, burnt leaf, and astringency based on the term and the definition. The mean scores for all 25 attributes are shown in
Table 2.
Green, brown, bitter, and astringent attributes were perceived throughout all five brewings of the green tea samples with a few exceptions at the fifth brew. Spinach, straw-like, and toothetch usually were present in at least the first three brews (
Table 2). The intensity of the green flavor generally decreased as the samples were brewed repeatedly. The change in the intensity of spinach flavor was similar to the pattern of the green flavor. In general, the brown flavor intensity decreased from the second brew onward. The intensity of brown note in the first brew and the second brew were not statistically different. The intensity of straw-like decreased as green tea was brewed repetitively, except in the
Myoungjeon sample where the highest intensity was in the second brew. The bitterness increased significantly from the first brew to the second brew in the
Daehan Ujeon,
Daehan Ujeon Wild,
Myoungjeon, and
Ouksu samples. The
Illohyang and
Ujeon Okro samples had similar bitterness intensities in both the first and the second brews. Beyond the second brew, the bitterness decreased significantly with each brew for all the samples. This is in partial agreement with findings that the percentage of caffeine, which is the major bitter substance in green tea, found in the green tea liquor decreased as the tea was brewed three times repeatedly [
18]. The astringency and toothetch had similar patterns to the bitterness with the intensity being the highest at the second brew and then subtly decreasing with each subsequent brewing.
Table 2.
Mean scores and significant differences in flavor attributes for green tea brewed five times.
Table 2.
Mean scores and significant differences in flavor attributes for green tea brewed five times.
| | Daehan Ujeon | Daehan Ujeon Wild | Illohyang |
|---|
| Brews | Brews | Brews |
|---|
| 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 |
|---|
| Green | 4.03 a1 | 3.31 b | 1.81 c | 0.91 d | 0.00 e | 2.67 a | 1.64 b | 1.44 b | 0.83 c | 0.64 c | 2.17 a | 1.42 b | 1.50 b | 0.94 c | 0.53 d |
| Asparagus | 1.66 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Celery | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Green beans | 0.75 a | 0.78 a | 0.00 b | 0.00 b | 0.00 b | 1.36 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Green herb-like | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Parsley | 0.00 b | 0.63 a | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Spinach | 1.88 a | 1.34 b | 0.69 c | 0.00 d | 0.00 d | 1.58 a | 1.22 ab | 0.82 b | 0.00 c | 0.00 c | 1.39 a | 0.72 b | 0.00 c | 0.00 c | 0.00 c |
| Brown | 2.75 a | 2.66 ab | 2.06 b | 1.13 c | 0.67 c | 3.83 a | 3.58 a | 2.03 b | 1.17 c | 0.53 d | 3.33 a | 3.47 a | 1.69 b | 1.00 b | 0.69 c |
| Ashy/sooty | 0.00 b | 0.50 a | 0.00 b | 0.00 b | 0.00 b | 0.00 c | 0.00 c | 0.94 a | 0.50 b | 0.00 c | 0.53 a | 0.86 a | 0.50 a | 0.00 b | 0.00 b |
| Burnt/scorched | 0.81 a | 1.09 a | 0.00 b | 0.00 b | 0.00 b | 1.11 a | 1.42 a | 0.00 b | 0.00 b | 0.00 b | 1.31 a | 1.22 a | 0.00 b | 0.00 b | 0.00 b |
| Straw-like | 1.41 a | 1.59 a | 1.25 a | 0.81 b | 0.00 c | 1.86 a | 1.89 a | 1.28 b | 0.72 c | 0.00 d | 1.44 a | 1.08 b | 0.92 b | 0.00 c | 0.00 c |
| Tobacco | 0.00 b | 0.00 b | 0.63 a | 0.00 b | 0.00 b | 1.00 ab | 1.36 a | 0.72 b | 0.00 c | 0.00 c | 1.19 a | 0.56 b | 0.00 c | 0.00 c | 0.00 c |
| Citrus | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 b | 0.00 b | 0.75 a | 0.00 b | 0.00 b |
| Floral/perfumy | 0.00 b | 0.69 a | 0.84 a | 0.63 a | 0.56 a | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.83 bc | 1.19 a | 1.17 ab | 0.83 bc | 0.56 c |
| Fruity | 0.72 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Grain | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 b | 0.64 a | 0.00 b | 0.00 b | 0.00 b |
| Medicinal | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Musty/new leather | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Nutty | 0.00 b | 0.66 a | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Seaweed | 2.28 a | 0.56 b | 0.00 | 0.00 | 0.00 | 2.28 a | 0.86 b | 0.00 c | 0.00 c | 0.00 c | 2.28 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b |
| Sweet aromatics | 0.57 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.53 a | 0.50 a | 0.00 b | 0.00 b | 0.00 b |
| Bitter | 6.91 b | 7.38 a | 5.63 c | 3.69 d | 2.34 e | 6.14 b | 6.72 a | 5.22 c | 3.64 d | 2.33 e | 6.44 a | 6.72 a | 5.47 b | 3.60 c | 2.47 d |
| Astringent | 1.81 a | 2.22 a | 2.06 a | 1.28 b | 0.53 c | 1.81 ab | 2.14 a | 1.69 ab | 1.53 b | 0.72 c | 1.58 b | 2.06 a | 2.03 a | 1.31 b | 1.00 c |
| Tooth-etch | 0.88 a | 1.31 a | 1.06 a | 0.59 b | 0.00 c | 1.14 a | 1.17 a | 0.89 ab | 0.67 bc | 0.50 c | 0.61 b | 1.03 a | 0.89 ab | 0.53 b | 0.00 c |
| | Myoungjeon | Ujeon Okro | Ouksu |
| Brews | Brews | Brews |
| 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 |
| Green | 3.97 a | 2.36 b | 2.03 bc | 1.64 c | 1.11 d | 2.51 a | 1.17 b | 0.57 c | 0.00 d | 0.00 d | 4.21 a | 4.24 a | 2.77 b | 1.62 cd | 1.42 d |
| Asparagus | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.59 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Celery | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 b | 0.00 b | 0.50 a | 0.00 b | 0.00 b |
| Green beans | 1.14 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.94 | 0.00 | 0.00 | 0.00 | 0.00 b | 1.03 a | 0.97 a | 0.00 b | 0.00 b |
| Green herb-like | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.64 a | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Parsley | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 b | 1.12 a | 0.00 b | 0.00 b | 0.00 b |
| Spinach | 2.08 a | 1.92 a | 1.28 b | 0.72 c | 0.00 c | 1.78 | 0.00 | 0.00 | 0.00 | 0.00 | 2.59 a | 2.53 a | 0.89 b | 0.79 b | 0.56 b |
| Brown | 3.97 a | 4.44 a | 2.36 b | 1.47 c | 1.11 c | 3.25 ab | 3.75 a | 3.03 ab | 2.59 c | 1.69 d | 2.28 ab | 2.64 a | 1.14 c | 1.55 bc | 0.00 d |
| Ashy/sooty | 0.00 c | 1.39 a | 1.00 ab | 0.67 b | 0.00 c | 0.00 d | 2.59 a | 2.63 a | 1.88 b | 1.28 c | 0.00 b | 0.00 b | 0.00 b | 0.59 a | 0.00 b |
| Burnt/scorched | 2.17 a | 2.33 a | 0.69 b | 0.00 c | 0.00 c | 1.63 a | 0.50 b | 0.00 c | 0.00 c | 0.00 c | 1.26 b | 2.35 a | 0.00 c | 0.00 c | 0.00 c |
| Straw-like | 1.17 bc | 2.00 a | 1.50 ab | 0.89 cd | 0.64 d | 1.90 a | 1.77 ab | 1.43 b | 1.43 b | 0.74 c | 1.52 a | 1.44 a | 0.94 b | 0.76 b | 0.00 c |
| Tobacco | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 c | 1.06 a | 0.94 ab | 0.50 b | 0.00 c | 0.00 b | 0.00 b | 0.00 b | 0.65 a | 0.00 b |
| Citrus | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Floral/perfumy | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Fruity | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Grain | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Medicinal | 0.00 b | 0.89 a | 0.94 a | 0.53 a | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Musty/new-leather | 0.00 c | 1.58 a | 0.72 b | 0.53 b | 0.00 c | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Nutty | 0.00 b | 0.56 a | 0.00 b | 0.00 b | 0.00 b | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Seaweed | 4.19 a | 0.69 b | 0.00 c | 0.00 c | 0.61 b | 2.22 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 1.91 a | 0.85 b | 0.00 c | 0.00 c | 0.00 c |
| Sweet aromatics | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 b | 0.00 b | 0.56 a | 0.00 b | 0.00 b | 0.00 b | 0.00 b | 0.71 a | 0.00 b | 0.59 a |
| Bitter | 7.14 b | 8.56 a | 6.25 c | 4.75 d | 3.42 e | 6.08 ab | 6.39 a | 5.61 b | 4.48 c | 3.54 d | 6.99 b | 7.84 a | 5.46 c | 3.93 d | 2.69 e |
| Astringent | 1.78 b | 2.83 a | 2.00 b | 1.42 c | 0.92 d | 1.32 b | 1.79 a | 1.54 b | 0.75 c | 0.57 c | 1.64 b | 1.97 a | 1.38 b | 0.94 c | 0.00 d |
| Tooth-etch | 0.81 b | 1.78 a | 1.06 b | 0.83 b | 0.00 c | 0.53 a | 0.81 a | 0.66 a | 0.00 b | 0.00 b | 0.53 b | 0.81 a | 0.66 b | 0.00 c | 0.00 c |
In addition to the green and spinach flavor notes, other green-related attributes were perceived: asparagus, celery, green beans, green herb-like, and parsley. The asparagus note was barely detected in the first brews of the Daehan Ujeon and Ujeon Okro samples. All the samples, except Illohyang,had green beans at barely detected to low levels in the first, the second, or the third brew. The celery was present in the third brew of the Ouksu sample. The fifth brew of the Myoungjeon sample had a green herb-like note at threshold level. The parsley was present in the Daehan Ujeon and Ouksu samples in the second brews.
Besides the brown and straw-like attributes, the brown-related attributes that were perceived were ashy/sooty, burnt/scorched, and tobacco. An ashy/sooty note was perceived in all of the samples but mainly in the second, the third, and the fourth brews. The burnt/scorched flavor was perceived at barely detected to low levels, the intensity ranging 0.5 to 2.35, mainly in the first and the second brews of all the Korean green teas. The tobacco was perceived in all the samples other than Myoungjeon, mostly in the second and the third brews.
Other attributes that were detected in the samples included citrus, floral/perfumy, fruity, grain, medicinal, musty/new leather, nutty, and seaweed. Many of these sensory attributes are present only in some teas and only during some brews, meaning that in many cases the attribute was not present and is shown by 0.0 in the table. This is not surprising given the unique nature of the falvor of green teas and the potential for the sensory properties to change during multiple brews of each tea.
The citrus was detected in the third brew of the
Illohyang sample. A floral/perfumy note was detected only in two of the samples,
Daehan Ujeon and
Illohyang, and was present from the second brew onward for the
Daehan Ujeon sample and in all the five brews for the
Illohyang sample at low intensities. The
Daehan Ujeon sample was the only one perceived as having a fruity note, and that was only in the first brew. Grain flavor was found only in the
Illohyang sample in the second brew. The
Myoungjeon sample was perceived to have medicinal note at a threshold level in the second, the third, and the fourth brews. The musty/new leather note was only detected in
Myoungjeon from the second brew to the fourth brew at very low levels. The nutty flavor was present only in the second brews of the
Daehan Ujeon and
Myoungjeon Samples. All six green tea samples had low seaweed flavors in the first brews and the
Daehan Ujeon,
Daehan Ujeon Wild,
Myoungjeon, and
Ouksu samples were perceived to have seaweed flavor at a low level in the second brews. The seaweed was also present in the fifth brew of the
Myoungjeon sample. The seaweed flavor was first researched and documented in 1977 [
3] and was later defined and referenced [
7] to describe the flavor of some green teas. However, it was not reported by researchers who have previously studied Korean green tea [
26,
27]. A sweet aromatics note was present at the threshold level in four of the samples (
Daehan Ujeon,
Illohyang,
Ujeon Okro and
Ouksu) at various brews.
The flavor of the green loose leaf tea samples changed when they were brewed multiple times. Generally, the flavor decreased as the number of brews increased in all the green tea samples in the current study. This trend is shown in PCA biplot (
Figure 1). The first two brews appeared to provide similar intensities of the flavor attributes, except for the intensities of the green-related attributes which actually decreased and the intensities of bitterness, astringency, and toothetch which increased from the first to the second brews.
Figure 1.
Principal component analysis biplot of descriptive sensory analysis of green teas a, b.
Figure 1.
Principal component analysis biplot of descriptive sensory analysis of green teas a, b.
a D = Daehan Ujeon; DW = Daehan Ujeon Wild; I = Illohyang; M = Myoungjeon; O = Ouksu; U = Ujeon Okro; Numbers following the sample name denotes number of brew; b Lines connect consecutive brews of the same green tea samples to show the trend of flavor change.
While the numbers of flavor attributes and their intensities decreased beyond the second brew, the third brew and even the fourth brew may be enjoyed by consumers who prefer a milder flavor and low bitterness and astringency in their green tea. The fifth brew presented a few flavor notes at low levels and low bitterness and astringency, suggesting that most of the flavor is gone by the fifth brew. Also, as shown in
Figure 1, the flavor changes occurring during the multiple brews of green tea is rather continuous and, because the flavors get weaker each time, the changes of flavor may appeal to some consumers.
3.2. Aroma Volatile Compounds
Fourteen aroma volatile compounds were identified and quantified in the green tea samples brewed five times (
Table 3). It must be remembered that these teas were extracted only with hot water and headspace was analyzed, much as tea might be smelled before tasting. Thus, because no chemical extraction was used and no intentional concentration of volatiles was done, the number of compounds is much lower than that reported in most previous studies. There were two aliphatic alcohols ((
z)-4-hexen-1-ol and 2-ethyl-1-hexanol), two aromatic alcohols (benzenemethanol and benzeneethanol), two terpene alcohol (linalool and geraniol), one aliphatic aldehyde (nonanal), two aromatic aldehydes (benzaldehyde and phenylacetaldehyde), three ketones (4-methyl-3-penten-2-one, jasmone, and β-ionone), one furan (linalool oxide), and two other compounds (1H-indole and 1-ethyl-1H-pyrrole-2-carboxaldehyde).
Table 3.
Fourteen volatile compounds found in six Korean green teas and Kovats retention indices calculation for the compounds.
Table 3.
Fourteen volatile compounds found in six Korean green teas and Kovats retention indices calculation for the compounds.
| Compounds | Kovats RI Calculated | Kovats RI Reported |
|---|
| 4-Methyl-3-penten-2-one | 815.8 | 800 [28] |
| (z)-4-Hexen-1-ol | 873.3 | 868 a |
| Benzaldehyde | 985.3 | 962 [29] |
| 2-Ethyl-1-hexanol | 1047.6 | 1028 [30] |
| Benzenemethanol | 1058.3 | 1033 [31] |
| Benzeneacetaldehyde | 1058.3 | 1045 [30] |
| Linalool oxide | 1094.8 | 1070 [32] |
| Linalool | 1126.5 | 1100 [33] |
| Nonanal | 1122.5 | 1103 [28] |
| Benzeneethanol | 1140.5 | 1113 [34] |
| Geraniol | 1234.0 | 1259 [35] |
| 1H-Indole | 1328.3 | 1286 [36] |
| Jasmone | 1421.6 | 1394 [36] |
| β-Ionone | 1405.4 | 1482 [30] |
The concentrations of these compounds are shown in
Table 4. The concentrations of the volatile compounds in the current study are generally lower than the threshold reported in previous literature.
We hypothesize that the reason for this is that green tea generally is consumed at a higher temperature whereas the typical threshold evaluation by previous researchers is conducted at room temperature. Also, the volatile compounds in tea are present in a complex matrix of volatiles whereas reported thresholds are for the simple compounds. The Kovats RI’s calculated based on retention time and previous reports by other researchers are shown in
Table 3.
The compounds also do not automatically decrease or increase over time. Although some of this may be sampling error, it also is quite likely that changes in the leaves as the teas are repeatedly doused with hot water in subsequent brews are likely to affect the release of compounds. For example, nonanal appears to generally increase in most teas suggesting that the leaves are releasing more of the compound as the cells in the leaves are disrupted during subsequent brewing. However, in some teas the nonanal decreases in some later samples suggesting that for those teas most of the nonanal has been released in prior brews.
Table 4.
Composition and concentration of the volatile compounds in six green teas infusion (μg/L).
Table 4.
Composition and concentration of the volatile compounds in six green teas infusion (μg/L).
| Compounds | Brew 1 | Brew 2 | Brew 3 | Brew 4 | Brew 5 |
|---|
| Daehan Ujeon | | | | | |
| Benzenemethanol | 4.84 | - | - | - | - |
| Linalool | - | 3.48 | 12.97 | 17.29 | - |
| Nonanal | 7.35 | 11.61 | 13.55 | 24.84 | 6.52 |
| 1H-Indole | 3.61 | - | - | - | - |
| Jasmone | 4.06 | - | 10.90 | 13.10 | - |
| Daehan Ujeon Wild | | | | | |
| 2-Ethyl-1-hexanol | - | 2.32 | - | - | - |
| Benzenemethanol | 3.42 | 4.26 | - | - | - |
| Linalool | - | 3.87 | - | - | - |
| Nonanal | 4.06 | 4.97 | 6.19 | - | 6.77 |
| 1H-Indole | - | 5.48 | - | - | - |
| Jasmone | - | 6.84 | - | - | - |
| Illohyang | | | | | |
| (z)-4-Hexen-1-ol | 2.84 | 1.87 | - | - | - |
| Linalool oxide | 4.06 | 3.29 | - | - | - |
| Linalool | 11.74 | 12.06 | 15.10 | 10.00 | 7.48 |
| Nonanal | 3.68 | 3.03 | 4.84 | 3.48 | 5.03 |
| Geraniol | 16.58 | 19.61 | 18.71 | 16.26 | 9.68 |
| Jasmone | 3.42 | 4.06 | 3.87 | 2.90 | - |
| Myoungjeon | | | | | |
| 4-Methyl-3-penten-2-one | 1.42 | - | - | - | - |
| Benzaldehyde | 0.90 | - | - | - | - |
| 2-Ethyl-1-hexanol | - | - | - | - | 4.52 |
| Benzeneacetaldehyde | 2.32 | - | - | - | - |
| Nonanal | - | - | - | - | 10.84 |
| Jasmone | 2.58 | - | - | - | - |
| Ouksu | | | | | |
| 4-Methyl-3-penten-2-one | 2.65 | 2.45 | - | - | - |
| Benzeneacetaldehyde | 1.74 | - | - | - | - |
| Linalool | - | - | 3.16 | - | - |
| Nonanal | 1.74 | 3.74 | 4.45 | - | 7.81 |
| Geraniol | 1.23 | - | - | - | - |
| Jasmone | 3.35 | 2.52 | - | 3.68 | - |
| β-Ionone | 2.32 | 3.55 | 2.39 | 1.87 | - |
| Ujeon Okro | | | | | |
| 4-Methyl-3-penten-2-one | 3.81 | | | | |
| Linalool | - | 13.74 | 9.29 | 6.26 | 6.84 |
| Nonanal | - | 9.81 | 4.77 | 6.26 | 9.10 |
| Benzeneethanol | - | 4.39 | - | - | - |
| Geraniol | - | 7.23 | 4.58 | 3.10 | - |
| Jasmone | - | 5.48 | 3.55 | 2.58 | - |
| β-Ionone | 2.26 | - | - | - | - |
(z)-4-Hexen-1-ol was present in the Illohyang sample at the first and the second brews. However, no literature on green tea volatiles reported this compound and no information regarding the aroma or flavor characteristics was found.
2-Ethyl-1-hexanol was detected in the
Daehan Ujeon Wild sample at the second brew and in the
Myoungjeon sample at the fifth brew only. The concentrations of the compound in these two samples were at 2.32 μg/L and 4.52 μg/L, respectively. It was previously reported in a Japanese green tea [
15] but no other literature has reported 2-ethyl-1-hexanol in green teas. It has a mild, oily, sweet and slight rose fragrance [
37].
Benzyl alcohol (benzenemethanol) was found in a few brews of the
Daehan Ujeon Wild Tea sample and the
Daehan Ujeon sample. It has a faint aromatic odor [
37] and has previously been found in Korean tea [
38]. Phenethyl alcohol (benzeneethanol) has a floral and rose odor [
37] and was found in the second brew of the
Ujeon Okro sample.
Linalool has been reported in green tea by many other researchers [
15,
38,
39,
40]. As expected, it was detected in all five samples except
Myoungjeon and was present in more than three consecutive brews in the
Daehan Ujeon,
Illohyang, and
Ujeon Okro samples
. Though, the trend of changes in the concentration for repeated brews differed among these samples. Linalool’s odor is similar to bergamot oil [
37] and citrus [
41]. It is detectable at as low as 0.087 μg/L and recognizable at as low as 0.17 μg/L [
41], which both are lower than our findings ranging from 3.16 μg/L to 15.10 μg/L.
Geraniol is another terpene alcohol and has a geranium odor [
37]. It was found in the
Illohyang and the
Ujeon Okro samples. The concentrations of geraniol in these two samples were the highest in the second brew and declined as they were brewed repeatedly. Geraniol has been found commonly in green teas [
38]. Its thresholds were reported as 1.1 μg/L for detection and 2.5 μg/L for recognition [
41].
Nonanal was present in all six samples in our study. However, the concentrations of nonanal in each brew did not have any perceivable trend. It has a tallow, fruity [
42], strong, fatty odor [
37], citrus-like and soapy [
41]. Its detection threshold was reported as 2.8 μg/L and its recognition threshold was reported as 8.0 μg/L [
41]. The nonanal was reported in a Korean commercial green tea made with tea leaves harvested in July and roast-processed [
43] but was not reported in the other studies with Korean green teas [
10,
11].
Benzaldehyde was only detected in the first brew of the
Myoungjeon sample. It is an aromatic aldehyde and has an almond odor [
37] and commonly is used in artificial cherry flavor to provide a strong fruity note. The benzaldehyde was commonly found in green teas from Korea in previous literature [
10,
11,
43]. The benzaldehyde may not be detected in more of our samples because of the sample preparation and the extraction technique. In the current study, brewed green tea liquor was used as a sample and the volatile compounds were extracted using SPME, which can detect the concentrations ranging from pg/g (ppt) to μg/g (ppm). The concentration of benzaldehyde in the second brew of the
Myoungjeon sample was 0.90 μg/L , which is 0.90 ppb.
Phenylacetaldehyde (benzeneacetaldehyde) was present in the first brews of the
Myoungjeon and the
Ouksu samples. It is an aromatic aldehyde and has a pungent, green, hyacinth-like, apricot, and berry-like flavor [
37].
4-Methyl-3-pentene-2-one was detected in the
Myoungjeon,
Ujeon Okro and
Ouksu samples. The concentrations ranged between 1.42 and 3.81 μg/L. It has a sweet, fruity odor and it is somewhat water soluble [
37]. It was reported in the Korean green tea along with a
Chunmee green tea and a
Gorreana green tea [
38].
Jasmone was found in all five samples except
Myoungjeon. However, it is hard to find any trend in the concentrations. The jasmone was reported in the previous research [
10,
39]. The jasmone is an aliphatic ketone and has a jasmine odor and a fruity flavor [
37].
β-Ionone was detected in four brews of the
Ouksu sample but concentration was lower than detection threshold reported [
41] except in the second brew. Others have found this compound in Korean green teas [
11,
39] as well as green teas from China [
40] and Japan [
15]. It has a woody odor [
37], flowery and violet-like [
41]. It was reported that one can detect the odor at 3.5 μg/L and can recognize it at 8.4 μg/L [
41].
Linalool oxide was found in the first two brews of the
Illohyang and the concentrations were around 4 μg/L. The linalool oxides were reported in the commercial Korean green teas made with tea leaves harvested in April and June [
10] but not in August [
11]. It has a sweet, lemon, cineol flavor [
37].
1H-indole was detected in a few brews of the
Daehan Ujeon and
Daehan Ujeon Wild samples. The concentrations were all below 6 μg/L. It has a floral, animal, jasmine and earthy odor and it is volatile with steam [
37]. The indole was also reported as having a fecal, mothball-like odor and the detection threshold was reported as 11 μg/L. In a previous study indole was reported as the most abundant volatile compound in the commercial Korean green tea samples, which were made with the tea leaves picked in April and June, but the concentrations were not reported [
10].
3.3. Relationships between Descriptive and Aroma Volatiles Analyses in Green Tea Samples
The partial least square regression (PLSR) was conducted to relate the instrumental data to the descriptive data for each brew. The PLSR biplots of the first and the second brews are shown in
Figure 2 and
Figure 3. When terms on the map are closer they represent a higher relationship among the attributes and chemical composition. Of 25 descriptive attributes, only the aromatic attributes were included for the analysis (excluding bitter, astringent, and tooth-etch, which are not dependent on volatile compounds). Generally, the number of sensory attributes perceived, their intensities, and the number of volatile compounds detected decreased markedly from the second brew to the third brew.
Twelve volatile compounds were detected by GC-MS and 16 sensory attributes were perceived by the trained panelists in the first brew (
Figure 2). The PLSR map shows that 95% of the instrumental data explained 38% of descriptive sensory data when the first two principal components were considered. The geraniol and linalool were explained mainly in the PC 1 and nonanal and benzenemethanol were explained in the PC 2. The geraniol, linalool and linalool oxide compounds were correlated with the floral/perfumy note. The nonanal, jasmone, and benzenemethanol compounds were related to the fruity and sweet aromatics notes.
Twelve volatile compounds and 16 sensory attributes were found in the second brews of the green tea samples (
Figure 3). The PLSR results indicated that 84% of the instrumental data explained 51% of the descriptive sensory data in the first two PCs. Geraniol and linalool were the main vectors in PC 1 and PC 2 was explained by nonanal, geraniol, and linalool. Geraniol, nonanal, and linalool oxide were also related to the floral/perfumy attributes.
Only five volatile compounds, but 14 sensory terms, were used to describe the third brews of green tea samples. Around 96% of the instrumental data explained 25% of the descriptive data in the first two PC’s. It appears that the floral/perfumy attributes are related to the presence of geraniol, linalool, and jasmone but it is hard to know for sure because the explanation rate of the descriptive data by the instrumental data was only 25%.
Five volatile compounds and nine sensory descriptive attributes were present in the samples brewed four times. The PLSR data showed that 88% of the instrumental data explained 37% of the descriptive sensory data. As expected, nonanal, linalool, jasmone, and geraniol were related to the floral/perfumy notes.
Only four volatile compounds were detected using GC-MS and nine flavor attributes were perceived in the fifth brew of green tea samples. The PLSR analysis showed that 87% of the instrumental data explained 54% of the descriptive sensory data. In the PLSR biplot, it was hard to draw any relationship between the volatile compounds and the descriptive attributes probably because of the low levels of both the attributes and the aroma compounds that were found in the fifth brew.
Figure 2.
Partial least square regression analysis of descriptive sensory and gas chromatography data for the first brew of green tea samples.
Figure 2.
Partial least square regression analysis of descriptive sensory and gas chromatography data for the first brew of green tea samples.
Figure 3.
Partial least square regression analysis of descriptive sensory and gas chromatography data for the second brew of green tea samples.
Figure 3.
Partial least square regression analysis of descriptive sensory and gas chromatography data for the second brew of green tea samples.
