-
The study analyzed crushed samples, as well as aroma water samples. The number of aroma-active compounds in the samples and their relative content was examined to select the best treatment method. As shown in Fig. 3, 24 aroma-active compounds were identified in the detected values of the two forms of samples, such as d-limonene, linalool, 2-methoxy-4-vinylphenol, furfural, and α-terpinene, etc.; aroma-active compounds specific to the heated enriched aroma-active water such as p-cymene, 1-octanol, 4-terpineol, etc. There were 19 kinds of aroma-active compounds particular to the directly crushed samples such as undecanal, citronellol, neral, etc. There were eight kinds of aromatic compounds.
Figure 3.
Comparison of aroma-active compounds in two forms, (a) concentration and number; (b) the number of compounds.
The relative content of aroma-active compounds was collected using the normalization method. The sum of the relative content of aroma-active compounds in the water sample was greater than that of the crushed sample, and the aroma-active compounds were also more in the aroma water sample. In conclusion, the experimental feasibility of studying the aroma-active compounds of aroma water met expectations, and the aroma-active compounds of the Xinhui Chenpi samples could be characterized in this way.
Quantitative analysis of aroma-active compounds
-
The GC-MS qualitative analysis of the volatile compounds contained in the aroma water detected a total of 24 volatile aroma-active compounds with a matching index greater than 80% compared with the database, including six alcohols, four olefins, three aldehydes, two ketones, one acid, three phenols and three esters, as shown in Table 1. The corresponding standard curves were established for each compound with good linearity (equations of standard curves, where y is the area of the peak of an authentic standard, and x is the concentration of the authentic standard). Among them, d-limonene (3,291.64 mg/kg) showed highest in all compounds, followed by linalool (561.39 mg/kg), 4-terpineol (370.81 mg/kg), γ-terpinene (354.97 mg/kg), furfural (274.80 mg/kg), 2-methoxy-4-vinylphenol (253.67 mg/kg) and α-terpineol (250.54 mg/kg). According to the available literature, compounds such as d-limonene, γ-terpinene, linalool, and myrcene are essential components of the aroma composition of Chenpi[25−30], and substances such as 4-terpineol, furfural, 2-methoxy-4-vinylphenol, and p-cymene in the Chenpi aroma-active substances have been rarely reported previously. In the present study, octanal (78.71 mg/kg), thymol (38.18 mg/kg), cymenol (29.62 mg/kg), and myrcene (21.19 mg/kg) were the compounds that contributed significantly to the aroma of Xinhui Chenpi.
Table 1. The concentration of volatile compounds detected in aroma water samples.
No Time
(min)RI Compound Molecular formula Calibration curves R2 Linear range
(mg/kg)Content
(mg/kg)aRSD (%)b 1 4.12 840 Furfural C5H4O2 y = 2.08E+09x + 1.76E+06 R2 = 0.9965 92.34-4.62 274.80 17.64 2 7.42 983 Myrcene C10H16 y = 3.55E+11x – 1.25E+07 R2 = 0.9939 1.37-0.07 21.19 24.52 3 7.74 1002 Octanal C8H16O y = 3.05E+10x – 4.37E+06 R2 = 0.992 2.34-0.12 78.71 31.41 4 8.19 1009 α-Terpinene C10H16 y = 2.73E+11x – 6.85E+06 R2 = 0.9919 0.51-0.03 3.47 27.55 5 8.44 1017 p-Cymene C10H14 y = 4.27E+11x – 5.02+05 R2 = 0.9959 0.41-0.02 12.85 13.06 6 8.60 1023 d-Limonene C10H16 y = 1.06E+11x + 2.55E+08 R2 = 0.9916 127.98-6.40 3291.64 28.02 7 9.53 1054 γ-Terpinene C10H16 y = 1.50E+11x – 3.95E+07 R2 = 0.9941 12.92-0.65 354.97 26.94 8 9.87 1071 1-Octanol C8H18O y = 1.62E+11x + 6.65E+06 R2 = 0.9923 0.40-0.04 3.32 20.64 9 10.91 1101 Linalool C10H18O y = 1.37E+11x + 9.32E+08 R2 = 0.9902 33.41-3.34 561.39 17.00 10 11.08 1105 Nonanal C9H18O y = 1.61E+11x + 4.96E+06 R2 = 0.9915 0.38-0.04 6.45 18.43 11 13.58 1168 1-Nonanol C9H20O y = 1.05E+11x + 3.83E+07 R2 = 0.9942 1.38-0.14 10.10 21.04 12 13.90 1192 4-Terpineol C10H18O y = 9.17E+10x + 3.02E+08 R2 = 0.9909 13.14-0.66 370.81 25.28 13 14.40 1202 α-Terpineol C10H18O y = 1.08E+11x + 1.66E+08 R2 = 0.9908 19.11-1.91 250.54 30.68 14 14.70 1219 Octanoic acid C8H16O2 y = 2.00E+09x + 1.41E+07 R2 = 0.9946 - - 15 16.52 1291 (-)-Carvone C10H14O y = 2.07E+11x + 4.62E+07 R2 = 0.9909 092-0.09 6.18 24.79 16 16.92 1304 Geraniol C10H18O y = 2.00E+11x + 4.34E+07 R2 = 0.9901 1.39-0.14 16.99 28.71 17 18.51 1358 Thymol C10H14O y = 6.54E+11x + 6.06E+08 R2 = 0.9922 7.88-0.79 38.18 26.40 18 18.89 1371 Cymenol C10H14O y = 6.14E+11x + 7.10E+07 R2 = 0.9916 0.77-0.08 29.62 21.95 19 19.40 1340 2-Methoxy-4-vinylphenol C9H10O2 y = 3.41E+10x + 2.15E+08 R2 = 0.9911 31.33-3.92 253.67 30.06 20 21.00 1360 Citronellyl acetate C12H22O2 y = 8.53E+11x + 1.20E+07 R2 = 0.9907 0.14-0.01 1.68 26.58 21 21.56 1380 n-Decanoic acid C10H20O2 y = 3.55E+11x – 1.42E+07 R2 = 0.9924 0.48-0.05 7.17 31.25 22 22.22 1385 Geranyl acetate C12H20O2 y = 1.01E+12x + 6.69E+06 R2 = 0.9906 0.08-0.008 0.54 30.38 23 23.22 1453 Methyl methanthranilate C9H11NO2 y = 1.16E+11x + 7.55E+06 R2 = 0.9914 0.53-0.05 15.20 10.21 24 26.40 1486 β-Ionone C13H20O y = 5.98E+11x + 3.47E+06 R2 = 0.9994 0.06-0.007 1.94 23.68 a: The data of concentration is mean (n = 3 for aroma water sample). b: The RSD is standard deviation (n = 3 for aroma water sample). −: Indicates no detection results. GC-O verifies the aroma-active compounds in samples
-
The odor activity of 24 aroma-active compounds detected by GC-MS was characterized by GC-O combined with AEDA and expressed as FD dilution factor, which was used in combination with the OAV value of each aroma-active compounds to verify its contribution to the aroma-active compounds of Xinhui Chenpi[24,31,32]. As shown in Table 2, the FD dilution factors ranged from 2 to 8,192, the higher FD factors, the stronger the odor of the compounds, and the greater the contribution to the aroma of the sample. The compounds with the highest FD factors were linalool (8,192) with sweet, cymenol (8,192) with pungent and refreshing odors, 2-methoxy-4-vinylphenol (8,192) with pungent and flower odors, followed by β-ionone (4,096) with woody odor, 4-terpineol (2,048) with woody and loamy incense odors, α-terpineol (2,048) with woody and flower odors, (−)-carvone (2,048) with mint and spicy odors, geranyl acetate (2,048) with medicinal odor, n-decanoic acid (2,048) with flower odor. The aroma-active compounds of Xinhui Chenpi are mainly alcohols, olefins, esters and aldehydes, and other compounds such as ketones and phenols. Among them, alcohols and olefins accounted for the highest proportion, such as d-limonene and linalool, which mainly show the typical orange and sweet odor of Chenpi, are the most abundant compounds in Xinhui Chenpi, with FD factors of 32 and 8,192, respectively. Aldehydes also contributed to the aroma-active formation of Chenpi, such as octanal, which has a typical orange flavor with an FD factor of 512. Furfural has a nut odor, which has rarely been reported in previous studies of aroma-active compounds of Chenpi.
Table 2. The FD factor of aroma-active compounds.
No Compound Odor description* FD** 1 Furfural Nut 8 2 Myrcene Pungent 32 3 Octanal Orange flavor 512 4 α-Terpinene Wax, orange 16 5 p-Cymene Refreshing 8 6 d-Limonene Citrus 32 7 γ-Terpinene Woody 8 8 1-Octanol Oily, fruity 128 9 Linalool Flowers, sweet 8192 10 Nonanal Oily, sweet, orange 8 11 1-Nonanol Orange scent 2 12 4-Terpineol Woody, loamy incense 2048 13 α-Terpineol Flowers, woody 2048 14 Octanoic acid Fruity 32 15 (−)-Carvone Mint, spicy 2048 16 Geraniol Rose 512 17 Thymol Medicine 1024 18 Cymenol Pungent, refreshing 8192 19 2-Methoxy-4-vinylphenol Pungent, flowers 8192 20 Citronellyl acetate Flowers 16 21 n-Decanoic acid Flowers 2048 22 Geranyl acetate Medicine 2048 23 Methyl methanthranilate Orange, flowers 1024 24 β-Ionone Woody 4096 * Description of the sniffing results by the sensory evaluator (n = 3 for sensory evaluator).
** Maximum dilution of the aroma-active compound.To identify the contribution of aroma-active compounds to the aroma of Xinhui Chenpi, the OAV was calculated to verify that each compound's odor threshold was known from the literature. The literature has reported that an aroma-active compound OAV ≥ 1 indicates that the compound contributes to aroma formation[24,33,34]. As shown in Table 3, the compounds have been ranked in order of OAV from largest to smallest. Octanoic acid was not detected in the content; other than that, all 22 aroma-active compounds revealed had OAV > 1 in aroma water. The results showed that d-limonene had the highest OAV (24,027) in all compounds, followed by linalool (20,050), 2-methoxy-4-vinylphenol (13,351), geraniol (1,699), thymol (382), octanal (342), α-terpineol (291), β-ionone (231). The above results show that the most important aroma-active compounds were d-limonene and linalool in Chenpi. Notably, although the contents of geraniol (16.99 mg/kg) and β-ionone (1.94 mg/kg) were not very high, their OAVs were the highest, because the thresholds were low (0.01 and 0.0084 mg/kg).
Table 3. The results of OAVs calculation of aroma-active compounds.
No Compound Concentration
(mg/kg)Odor threshold in
water (mg/kg)OAV 6 d-Limonene 3291.64 0.14b 24026.58 9 Linalool 561.39 0.03a 20049.61 19 2-Methoxy-4-vinylphenol 253.67 0.02b 13351.10 16 Geraniol 16.99 0.01a 1699.27 17 Thymol 38.18 0.10b 381.80 3 Octanal 78.71 0.23b 342.23 13 α-Terpineol 250.54 0.86b 291.32 24 β-Ionone 1.94 0.01c 231.49 18 Cymenol 29.62 0.18b 164.56 8 1-Octanol 3.32 0.02b 144.30 15 (-)-Carvone 6.18 0.07a 92.26 1 Furfural 274.80 3.00c 91.60 10 Nonanal 6.45 0.10a 64.50 12 4-Terpineol 370.81 6.40a 57.94 21 n-Decanoic acid 7.17 0.13b 55.19 23 Methyl methanthranilate 15.20 0.35b 43.54 2 Myrcene 21.19 0.67a 31.63 11 1-Nonanol 10.10 1.00a 10.10 7 γ-Terpinene 354.97 55.00c 6.45 22 Geranyl acetate 0.54 0.15a 3.60 5 p-Cymene 12.85 7.20b 1.78 20 Citronellyl acetate 1.68 1.00b 1.68 4 α-Terpinene 3.47 2.40b 1.45 14 Octanoic acid − 0.86b − Odor thresholds in water found in the literature. a: Indicates reference[18]. b: Indicates reference[35]. c: Indicates reference[21]. −: Indicates no detection. Release pattern of aroma-active compounds
-
The changes of 24 aroma-active compounds with heating time when samples were heated to enrich the aroma-active compounds were averaged over three replicate values. As shown in Table 4 and Fig. 4, a decreasing pattern was seen, with a sharp decrease after the 1st time, and a slight increase from the 2nd to the 3rd time, followed by a slight decrease.
Table 4. Changes in the concentration of aroma-active compounds of Chenpi with extraction time.
Time (min) Compound Concentration (mg/Kg) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 4.12 Furfural 4.07 2.46 2.49 2.48 2.59 2.69 2.71 2.70 2.53 2.41 2.24 2.32 2.63 2.58 2.54 2.66 2.70 2.61 2.51 2.21 7.42 Myrcene 1053.51 0.37 0.25 0.22 0.31 0.40 0.19 0.51 0.20 0.37 0.35 0.39 1.09 0.44 0.85 0.69 1.20 0.77 0.77 0.98 7.74 Octanal 69.18 4.19 6.48 5.87 6.80 5.30 6.97 5.64 5.25 5.56 5.53 5.08 6.29 4.98 5.10 4.96 5.89 7.61 5.99 4.75 8.19 α-Terpinene 114.06 0.56 0.59 0.36 0.52 0.51 0.44 0.56 0.50 0.52 0.56 0.42 0.75 0.59 0.78 0.72 1.10 0.97 0.88 1.11 8.44 p-Cymene 53.16 1.18 1.18 0.89 1.24 1.18 0.88 1.38 0.82 1.16 1.17 1.17 1.34 1.34 0.72 1.71 1.58 1.41 1.33 1.97 8.60 d-Limonene 36762.66 20.30 20.33 21.24 20.29 21.32 18.23 44.92 20.00 32.18 30.15 33.80 45.82 36.91 42.08 30.50 20.79 21.79 29.84 26.29 9.53 γ-Terpinene 3591.33 1.63 1.52 1.72 1.81 1.61 1.59 3.73 1.78 2.80 2.76 3.12 4.00 3.05 3.77 4.13 3.67 4.07 3.65 3.33 9.87 1-Octanol 20.45 2.86 2.86 1.72 1.87 1.81 1.42 1.08 1.17 1.02 0.88 1.11 0.75 0.58 0.47 0.39 0.45 0.55 0.42 - 10.91 Linalool 1080.19 396.41 408.52 350.55 346.02 352.47 270.33 240.68 232.30 211.12 194.25 173.38 180.08 161.11 140.28 138.62 121.05 112.08 61.12 59.41 11.08 Nonanal 58.69 3.08 3.30 3.00 3.72 3.61 3.49 2.96 2.91 3.43 3.59 3.29 3.56 3.28 3.50 3.56 3.54 3.34 3.04 3.39 13.58 1-Nonanol 16.30 7.72 7.62 7.31 6.96 6.80 6.62 5.51 4.71 3.90 3.23 3.29 3.28 3.23 3.29 3.36 2.98 3.00 2.97 2.79 13.90 4-Terpineol 498.61 147.36 144.59 136.17 133.69 123.46 117.43 108.56 112.45 110.63 104.22 104.54 103.89 103.29 102.11 106.10 89.27 84.65 50.56 79.04 14.40 α-Terpineol 394.39 134.60 127.01 114.39 113.81 100.99 79.61 68.79 70.19 67.84 61.17 56.70 56.03 56.12 55.62 55.00 43.90 41.62 41.01 40.69 14.70 Octanoic acid − 4.28 4.11 − − − − − − − − − − − − − − − − − 16.52 (−)-Carvone 30.11 15.90 14.41 13.32 11.47 9.65 6.81 5.31 4.92 4.14 3.34 2.86 2.87 2.10 1.84 1.55 1.04 0.98 0.91 0.78 16.92 Geraniol 24.16 18.26 17.67 15.09 14.85 13.24 10.37 7.84 8.16 7.78 6.63 5.70 5.60 5.28 4.82 4.95 3.85 3.43 2.84 2.66 18.51 Thymol 207.17 187.75 184.75 180.91 168.43 134.25 103.75 86.04 83.95 74.10 57.64 54.99 51.60 47.08 40.06 38.67 28.19 23.13 18.93 17.40 18.89 Cymenol 72.98 152.32 175.42 189.58 198.40 198.78 116.71 82.08 20.87 20.15 20.01 20.93 21.03 27.24 30.94 24.91 8.89 7.49 14.32 13.62 19.40 2-Methoxy-4-vinylphenol 22.97 23.21 31.70 62.03 68.22 71.49 54.06 53.21 51.45 50.46 50.34 50.10 49.72 48.85 48.53 49.54 49.70 44.43 44.72 39.54 21.00 Citronellyl acetate 21.93 5.32 5.30 5.20 5.55 5.26 3.65 3.40 1.73 1.52 1.48 1.41 1.73 1.67 1.48 1.44 1.56 1.46 1.86 2.09 21.56 n-Decanoic acid − 12.05 14.52 14.52 15.45 16.58 12.05 10.00 8.03 7.42 7.31 7.73 7.30 7.33 5.27 5.73 5.61 5.11 5.72 5.50 22.22 Geranyl acetate 7.13 1.12 1.16 1.29 1.16 1.29 1.20 1.18 1.18 1.16 1.16 1.15 1.16 1.04 1.16 1.17 1.09 1.09 1.18 1.13 23.22 Methyl methanthranilate − 5.12 6.93 5.65 5.02 4.89 4.84 4.82 3.10 2.82 2.52 2.16 1.98 1.68 1.54 1.49 1.43 1.05 0.89 0.73 26.40 β-Ionone 7.72 6.95 5.23 4.88 4.88 3.82 3.21 3.02 2.85 2.62 2.36 2.23 2.06 1.84 1.72 1.66 1.46 1.09 0.99 0.99 Total concentration 44839.78 1155.54 1187.93 1138.38 1132.86 1081.40 826.57 743.90 641.10 615.12 562.88 537.87 554.55 521.93 498.49 483.52 400.94 373.74 326.45 310.42 - indicates no detection. As shown in Table 4, the nine compounds including furfural, myrcene, octanal, α-terpinene, p-cymene, d-limonene, γ-terpinene, nonanal, and geranyl acetate showed a pattern of rapidly decreasing to a minimum and then being continuously maintained; the 10 compounds including 1-octanol, linalool, 1-nonanol, 4-terpineol, α-terpineol, (−)-carvone, geraniol, thymol, citronellyl acetate, β-ionone showed a gradually decreasing pattern; cymenol, 2-methoxy-4-vinylphenol, n-decanoic acid, and methyl methanthranilate showed a pattern of increasing first, reaching a maximum value, and then gradually decreasing; octanoic acid was detected only in the 2nd and 3rd times.
The alcohols and ketones in the aroma-active compounds of Xinhui Chenpi mainly showed a gradually decreasing pattern. For example, among the alcohols, linalool (1,080.19 mg/kg), 4-terpineol (498.61 mg/kg), α-terpineol (394.39 mg/kg) are of the highest proportion, linalool decreased from 1,080.19 mg/kg to 59.41 mg/kg; 4-terpineol decreased from 498.61 mg/kg to 79.04 mg/kg; α-terpineol decreased from 394.39 mg/kg to 40.69 mg/kg. This indicates that the alcoholic compounds of Xinhui Chenpi are persistent in aroma and slow in release.
The olefins and aldehydes mainly showed a pattern of rapidly decreasing at the lowest level and then being continuously maintained. Among the olefins, d-limonene (36,762.66 mg/kg), γ-terpinene (3,591.33 mg/kg), myrcene (1,053.51 mg/kg) and α-terpinene (114.06 mg/kg) are of the highest proportion, and d-limonene decreased from 36,762.66 mg/kg to 20.30 mg/kg in the 2nd and maintained since then; The γ-terpinene decreased from 3,591.33 mg/kg to 1.63 mg/kg in the 2nd and maintained since then; Myrcene decreased from 1,053.51 mg/kg to 0.37 mg/kg in the 2nd and maintained since then; α-terpinene decreased from 114.06 mg/kg to 0.56 mg/kg in the 2nd and maintained at a consequent level after that. It indicates that the olefins of Xinhui Chenpi are easily soluble and released extremely fast.
Other compounds, such as thymol gradually decreased from 207.17 mg/kg to 17.40 mg/kg; cymenol gradually increased from the initial 72.98 mg/kg, reaching a maximum value of 198.78 mg/kg at the 6th pass, and then started to decrease to 13.62 mg/kg; 2-methoxy-4-vinylphenol gradually increased from the initial 22.97 mg/kg to a maximum of 71.49 mg/kg at the 6th time and then started to decline to 39.54 mg/kg. This indicates that the aroma was persistent and remained in the release phase during the heating extraction.
Furfural differed from the other substances, with a small amount of 4.07 mg/kg initially, which decreased to 2.46 mg/kg in the 2nd and then continued to be maintained, indicating that Furfural is more difficult to volatilize than the other substances.
-
Aroma water obtained by heating and enrichment has obvious advantages. The aroma water of Xinhui Chenpi was comprehensively analyzed using the methods of GC-MS, GC-O and AEDA. It was concluded that linalool, d-limonene, 2-methoxy-4-vinylphenol, and α-terpineol were the four aroma-active compounds with high content and high contribution to the aroma formation, which were identified as the essential aroma substances of Xinhui Chenpi, and mainly presenting orange, sweet, spicy, woody and floral aromas. The heat release pattern was studied, and the results showed that the content of the aroma-active compounds generally showed a decreasing pattern with the heating time in the process of heating enrichment. In particular, the overall content decreased sharply after the 1st time, and it was speculated that this occurred because the Chenpi samples were soaked in heated water before being enriched by heating and distillation. However, this conclusion needs to be further verified. Although the overall content changed significantly after the 1st time, and combined with the respective emission pattern of 24 aroma-active compounds, it is difficult to volatilize all the aroma-active compounds in a short time, so this experiment recommends that the first 10 times of aroma water can be collected to achieve a shorter time and enrichment of the most aroma-active compounds.
-
About this article
Cite this article
Yang D, Wu X, Shi H, Zhang J, Wang C. 2022. Essential aroma substances and release pattern of Xinhui Chenpi. Beverage Plant Research 2:22 doi: 10.48130/BPR-2022-0022
Essential aroma substances and release pattern of Xinhui Chenpi
- Received: 12 September 2022
- Accepted: 16 November 2022
- Published online: 09 December 2022
Abstract: This study focuses on analyzing aqueous solutions of aroma-active compounds in Xinhui Chenpi distilled after being heated with headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC/MS). Feasibility of this method was also tested by comparison with crushed samples. The study also analyzed the aqueous solutions of the aroma-active compounds employing gas chromatography-olfactometry (GC-O) defense, aroma extraction dilution analysis (AEDA) and odor activity value (OAV) as well as their emission patterns. According to the study, there are 24 major aroma-active detected in the aqueous solution. Linalool, d-limonene, 2-methoxy-4-vinylphenol, and α-terpineol with sweet, spicy, and woody aroma contributed the most to the aroma-active compounds and were considered to be the essential aroma substances of Chenpi. When heated, the aroma of aromatic-active compounds rich in Chenpi volatilized rapidly and the release dropped dramatically in a short time. The substantial aroma-active compounds can be collected from the first ten released segments.