Figures (5)  Tables (2)

    • Figure 1. 

      Overall aroma profiles of the infusion (orange color) and the empty cup (blue color) of 'Dahongpao' tea. Odor notes with * means significantly different (p < 0.05), ** means extremely different (p < 0.01), and without * means not significantly different (p > 0.05).

    • Figure 2. 

      Total ion chromatographs (TICs) and key different odorants of the infusion and the empty cup of 'Dahongpao' tea.

    • Figure 3. 

      Effect of caffeine on the detection probability of four flowery and fruity compounds in water. (a) δ-decalactone + 638.9 mg/L CAF; (b) 6-methyl-5-hepten-2-one + 638.9 mg/L CAF; (c) (E,E)-2,4-heptadienal + 638.9 mg/L CAF; (d) Methyl phenylacetate + 638.9 mg/L CAF.

    • Figure 4. 

      The potential micromorphology of the aqueous solution of odorants with and without the addition of caffeine.

    • Figure 5. 

      Interactions between four aroma-active compounds, caffeine, and water. (a) (E,E)-2,4-heptadienal, caffeine, and water. (b) Methyl phenylacetate, caffeine, and water. (c) δ -declactone caffeine, and water. (d) 6-Methyl-5-hepten-2-one caffeine, and water.

    • No.a CAS No. Odorants Odor qualityb Identification
      methodc      		 RId (DB-5) AIe
      Detection NIST Infusion Empty cup
      1 66-25-1 Hexanal Green, grassy MS/O/RI/STD 801 801 n.d.a 1 ± 0.4b
      2 108-38-3 1,3-Dimethylbenzene Flowery MS/RI/STD 869 866 n.d. n.d.
      3 100-41-4 Ethylbenzene Flowery MS/RI 875 868 n.d. n.d.
      4 110-43-0 2-Heptanone Fruity, soapy, sweet MS/O/RI/STD 893 891 0.8 ± 0.2ga 2.1 ± 0.4bf
      5 111-71-7 Heptaldehyde Citrus-like, fatty MS/RI/STD 902 901 n.d. n.d.
      6 123-32-0 2,5-Dimethyl pyrazine Nutty MS/RI/STD 913 916 n.d. n.d.
      7 106-70-7 Methyl hexanoate Fruity, musty MS/RI/STD 926 925 n.d. n.d.
      8 13894-62-7 Methyl-(Z)-3-hexenoate Fruity, flowery MS/RI 933 933 n.d. n.d.
      9 100-52-7 Benzaldehyde Bitter almond-like MS/O/RI/STD 965 962 n.d.a 1.5 ± 0.3b
      10 110-93-0 6-Methyl-5-hepten-2-one Citrus-like, fruity MS/O/RI/STD 986 986 2.1 ± 0.6a 2.5 ± 0.3a
      11 3777-69-3 2-Pentylfuran Vegetable-like MS/RI/STD 990 993 n.d. n.d.
      12 4313-03-5 (E,E)-2,4-heptadienal Fatty, flowery MS/O/RI/STD 998 1012 2.1 ± 0.4a 2.2 ± 0.3a
      13 13360-64-0 5-Methyl-2-ethylpyrazine Nutty, roasty MS/RI/STD 1004 1005 n.d. n.d.
      14 138-86-3 Limonene Citrus-like MS/RI 1039 1031 n.d. n.d.
      15 2408-37-9 2,6,6-Trimethylcyclohexanone Spicy MS/RI 1044 1036 n.d. n.d.
      16 122-78-1 Phenylacetaldehyde Flowery, honey-like MS/O/RI/STD 1055 1045 1.7 ± 0.3a n.d.b
      17 2167-14-8 1-ethyl-1H-pyrrole-2-carbaldehyde Roasty MS/RI/STD 1063 1067 n.d. n.d.
      18 2548-87-0 (E)-2-octenal Fatty, nutty MS/RI/STD 1070 1060 n.d. n.d.
      19 30086-02-3 (E,E)-3,5-octadien-2-one Fruity MS/O/RI/STD 1083 1072 1.5 ± 0.4a 2.5 ± 0.5a
      20 5989-33-3 (Z)-linalool oxide (furanoid) Earthy, flowery, woody MS/RI/STD 1086 1074 n.d. n.d.
      21 13925-07-0 3,5-Dimethyl-2-ethylpyrazine Earthy, nutty MS/O/RI/STD 1090 1084 n.d.a 1.5 ± 0.2b
      22 78-70-6 Linalool Citrus-like, flowery MS/O/RI/STD 1114 1099 2.5 ± 0.2a n.d.b
      23 124-19-6 Nonanal Citrus-like, soapy MS/RI/STD 1118 1104 n.d. n.d.
      24 39741-41-8 2-Acetyl-1-ethylpyrrole Nutty MS/O/RI/STD 1126 1113 1.5 ± 0.3a n.d.b
      25 101-41-7 Methyl phenylacetate Fruity, flowery MS/O/RI/STD 1180 1178 2.2 ± 0.2a 2.1 ± 0.1a
      26 1438-94-4 1-Furfurylpyrrole Fruity, vegetable-like MS/O/RI/STD 1183 1187 1.8 ± 0.2a n.d.b
      27 16491-36-4 (Z)-3-hexenyl butyrate Fruity MS/RI 1186 1187 n.d. n.d.
      28 91-20-3 Naphthalene Tar-like, smoky MS/RI/STD 1192 1182 n.d. n.d.
      29 119-36-8 Methyl salicylate Fatty, tallowy, terpene-like MS/RI/STD 1196 1192 n.d. n.d.
      30 112-31-2 Decanal Soapy, citrus-like MS/O/RI/STD 1207 1206 2.5 ± 0.2a n.d.b
      31 35154-45-1 (Z)-3-hexenyl isovalerate Fruity MS/O/RI 1213 1218 n.d.a 2.1 ± 0.2b
      32 432-25-7 β-cyclocitral Fruity, flowery MS/O/RI/STD 1223 1220 1.7 ± 0.3a n.d.b
      33 106-24-1 Geraniol Rose-like, citrus-like MS/O/RI/STD 1250 1255 2.8 ± 0.2a n.d.b
      34 6290-37-5 2-Phenylethyl hexanoate Flowery MS/O/RI 1255 1650 2.3 ± 0.4a n.d.b
      35 141-27-5 Geraniol Citrus-like MS/O/RI 1268 1270 1.8 ± 0.2a n.d.b
      36 120-72-9 Indole Mothball-like MS/O/RI/STD 1295 1294 n.d.a 1.5 ± 0.3b
      37 30364-38-6 1,1,6-Trimethyl-1,2-dihydronaphthalene Petrol-like MS/RI 1358 1354 n.d. n.d.
      38 31501-11-8 (Z)-3-hexenyl hexanoate Fruity MS/O/RI/STD 1378 1379 1.7 ± 0.3a n.d.b
      39 6378-65-0 Hexyl hexanoate Fruity MS/O/RI 1383 1384 1.5 ± 0.3a n.d.b
      40 488-10-8 (Z)-jasmone Flowery, celery MS/O/RI/STD 1394 1394 1.7 ± 0.2a n.d.b
      41 127-41-3 α-ionone Flowery, raspberry-like MS/O/RI/STD 1423 1426 2.3 ± 0.3a n.d.b
      42 3796-70-1 Geranyl acetone Fruity, flowery MS/O/RI/STD 1446 1453 2 ± 0.5a n.d.b
      43 79-77-6 (E)-β-ionone Flowery, violet-like MS/O/RI/STD 1480 1486 n.d.a 2 ± 0.4a
      44 23267-57-4 β-ionone epoxide Fruity, sweet, flowery MS/RI/STD 1483 1473 n.d. n.d.
      45 705-86-2 δ-decalactone Coconut-like MS/O/RI/STD 1494 1496 2.8 ± 0.2a 2.5 ± 0.3a
      46 17092-92-1 Dihydroactinidiolide Coumarin MS/O/RI/STD 1533 1532 1.5 ± 0.2a n.d.b
      47 40716-66-3 (E)-nerolidol Flowery, citrus-like, woody MS/O/RI/STD 1561 1564 n.d.a 2 ± 0.2b
      48 1211-29-6 Methyl jasmonate Flowery MS/RI 1642 1641 n.d.a n.d.b
      a The compounds were numbered by the RI values. b The odor quality was described as the panelists recorded at the sniffing port. c MS, mass spectra; RI, retention index; O, olfactometry; STD, authentic reference compounds. d Retention index (RI) was determined using a series of n-alkanes standard (C7−C40) in DB-5 column. e The averaged aroma intensities (AI) perceived in ODP3 by three panelists. f Values with different Roman letters (a, b) in the same row are significantly different according to the Duncan test (p < 0.05), the result retains two significant digits. g Data are presented as the mean ± SD. The odor intensity was averagely scored from 0 to 3 at a unit of 0.1 (0 was 'scarcely sensed', 1 was 'sensed but scarcely recognized', 2 was 'significantly sensed and recognized', and 3 was 'mightily sensed and recognized').

      Table 1. 

      Aroma-active compounds in the infusion and the empty cup of 'Dahongpao' tea identified by HS-SPME-GC-MS-O.

    • Odorant Odor quality Odor threshold (μg/kg) Da
      Water Caffeine-containing
      aqueous solution
      δ-decalactone Coconut-like 8.08 6.52 0.81
      6-Methyl-5-hepten-
      2-one      		 Citrus-like, fruity 56.42 34.12 0.60
      (E,E)-2,4-heptadienal Fatty, flowery 29.55 14.61 0.49
      Methyl phenylacetate Fruity, flowery 12.12 9.05 0.75
      a D were represented as the ratio of the odor thresholds of odorants in the caffeine-containing aqueous solution and the corresponding odor thresholds in water.

      Table 2. 

      Odor thresholds of key flowery and fruity compounds in water and caffeine-containing aqueous solution.