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To investigate the aroma-contributing components in watermelon-flavored e-liquid for Vape, direct injection combined with gas chromatography-mass spectrometry (GC-MS) was employed to analyze the volatile components in three different brands of watermelon-flavored e-liquids. The results identified a total of 99 volatile components across the three samples. Sample A contained 76 components, Sample B contained 56, and Sample C contained 44. The three watermelon-flavored e-liquids shared 28 common volatile components. Sample A had 29 unique components, Sample B had 15, and Sample C had 6. Sensory evaluation results ranked the samples as A > B > C. Through flavor replication experiments, a novel e-liquid with watermelon flavor was successfully developed, exhibiting a natural, refreshing, and pleasant aroma.
The electronic cigarette industry has experienced rapid growth in recent years, with e-liquids offering diverse flavor profiles that significantly expand beyond the limitations of traditional cigarette aromas. Fruit-flavored electronic cigarette products, in particular, are highly favored by consumers. Watermelon, belonging to the Cucurbitaceae family and genus Citrullus, possesses high nutritional and economic value as a key fruit crop. Its aroma is characterized by freshness, sweetness, and transparency. Current domestic and international research on watermelon aroma primarily focuses on the flavor of watermelon juice and changes during processing, with limited reports on volatile component analysis in watermelon-flavored products. This study comparatively analyzes the volatile components in three watermelon-flavored e-liquids from different companies and brands, and develops a novel watermelon-flavored e-liquid, aiming to provide references for the development and replication of fresh fruit-flavored e-liquids for Vape.
1.1 Materials
Three different brands of watermelon-flavored e-liquids (Samples A, B, and C) were purchased from the market from three different companies in 2023.
1.2 Instruments and Equipment
Agilent 5977B gas chromatography-mass spectrometer (USA); Agilent 7890B gas chromatograph (USA).
1.3 Methods
1.3.1 Sample Preparation and Analysis
A 0.8 μL sample of e-liquid was directly injected. Analysis conditions were referenced from Han Xiaozhe.
Chromatographic conditions: Column type HP-5MS (60 m × 0.25 mm × 0.25 μm); Inlet temperature: 250°C; Column head pressure: 58 kPa; Injection mode: Split 40:1; Temperature program: Initial temperature 50°C, ramped at 4°C/min to 250°C, held for 10 min.
Mass spectrometry conditions: EI source, electron energy 70 eV; Electron multiplier voltage: 1800 V; Mass scan range: 33-250 amu; Ion source temperature: 230°C; Transfer line temperature: 280°C; NIST11 library search.
1.3.2 Qualitative and Quantitative Analysis
Compounds were identified through NIST library search combined with manual mass spectrum interpretation. Relative content of each component was calculated using peak area normalization (percentage of peak area).
1.3.3 Sensory Evaluation Analysis
Sensory evaluation was conducted by the e-cigarette evaluation team at Shenzhen Boton Flavor Co., Ltd., using a 9-point scoring system across eight individual indicators: aroma quality, aroma quantity, off-notes, concentration, throat hit, irritation, sweetness, and aftertaste.
2.1 Qualitative Analysis of Volatile Components in Three Watermelon-Flavored E-Liquids
GC-MS analysis was performed on the three watermelon-flavored e-liquids using the described method, yielding total ion chromatograms as shown in Figure 1.
Figure 1 GC-MS total ion chromatograms of volatile components in three watermelon-flavored vape aerosols
Sample A Sample B Sample C
Compounds with reliability above 80% were selected for identification via computer search of the mass spectral standard library. Volatile components were quantified using chromatographic peak area normalization, as detailed in Table 1. Sample A detected 76 volatile compounds, Sample B detected 56, and Sample C detected 44. Excluding overlaps, a total of 99 volatile components were identified across the samples. The sum of the identified compound peak areas accounted for 99.907%, 99.999%, and 99.965% of the total volatile component peak areas from direct injection for each sample, respectively.
2.2 Comparative Analysis of Volatile Components in Three Watermelon-Flavored E-Liquids
As shown in Table 1, the three watermelon-flavored e-liquids shared 28 common components (including trace amounts): ethanol, acetic acid, ethyl acetate, acetaldehyde propylene glycol acetal, ethyl propionate, isobutyl acetate, propylene glycol, ethyl butyrate, ethyl 2-methylbutyrate, leaf alcohol, isoamyl acetate, 2-methylbutyl acetate, 6-methyl-5-hepten-2-one, hexyl acetate, melon aldehyde, isoamyl butyrate, glycerol, benzoic acid, WS-23, nicotine, etc. The sum of these peak areas accounted for 99.441%, 97.875%, and 97.993% of the total detected volatile component peak areas in the samples, respectively. Among the 28 shared components, those with significant content differences included ethanol, isobutyl acetate, propylene glycol, ethyl butyrate, isoamyl acetate, glycerol, benzoic acid, WS-23, and nicotine; the sum of their relative contents was 98.404%, 96.739%, and 96.814% in the three samples.
Table 1 Analysis and comparison of volatile components of three watermelon-flavored e-cigarette aerosols
| No. | Compound Name | Sample A | Sample B | Sample C |
|---|---|---|---|---|
| 1 | Ethanol | 9.065 | 11.514 | 5.148 |
| 2 | Acetic acid | 0.130 | 0.158 | 0.001 |
| 3 | Ethyl acetate | 0.120 | 0.312 | – |
| 4 | Isobutanol | 0.006 | trace | – |
| 5 | Acetaldehyde propylene glycol acetal | 0.001 | trace | – |
| 6 | Propyl acetate | 0.005 | 0.027 | 0.071 |
| 7 | Ethyl propionate | 0.110 | trace | 0.005 |
| 8 | Butyl acetate | – | – | – |
| 9 | Acetaldehyde diethylene glycol acetal | – | trace | – |
| 10 | Isoamyl alcohol | 0.009 | 0.182 | – |
| 11 | Isobutyl acetate | 0.303 | 1.729 | 0.283 |
| 12 | Methyl 2-methylbutyrate | 0.039 | – | – |
| 13 | Propylene glycol | 51.846 | 44.123 | 41.269 |
| 14 | Ethyl butyrate | 0.116 | 0.240 | 0.989 |
| 15 | Butyl acetate | trace | 0.031 | 0.023 |
| 16 | Ethyl 2-methylbutyrate | 0.029 | 0.006 | – |
| 17 | Ethyl isovalerate | 0.003 | trace | 0.015 |
| 18 | Leaf alcohol (cis-3-hexenol) | 0.268 | 0.104 | 0.237 |
| 19 | 2-Methylbutanoic acid | 0.016 | 0.006 | – |
| 20 | trans-2-Hexenol | trace | – | – |
| 21 | Hexanol | 0.086 | – | – |
| 22 | Ethyl 2-methylbutyrate acetate | 0.229 | 1.326 | 0.067 |
| 23 | Isoamyl acetate | 0.027 | 0.135 | 0.007 |
| 24 | Propylene glycol acetate | 0.001 | trace | 0.007 |
| 25 | Ethyl acetoacetate | – | – | 0.002 |
| 26 | Ethyl hexanoate | 0.010 | – | – |
| 27 | Benzaldehyde | trace | – | – |
| 28 | 6-Methyl-5-hepten-2-one | 0.002 | 0.023 | 0.009 |
| 29 | β-Myrcene | trace | – | – |
| 30 | 6-Methyl-5-heptenol | trace | – | – |
| 31 | Hexanoic acid | 0.001 | – | – |
| 32 | Cis-3-hexenyl acetate | 0.013 | 0.001 | – |
| 33 | Hexyl acetate | 0.042 | 0.011 | 0.013 |
| 34 | trans-2-Hexenyl acetate | trace | – | – |
| 35 | p-Cymene | trace | – | – |
| 36 | Limonene | 0.062 | trace | 0.065 |
| 37 | Benzyl alcohol | 0.508 | – | – |
| 38 | 1,8-Cineole | trace | trace | – |
| 39 | Dipropylene glycol | – | – | – |
| 40 | Butyl valerate | trace | 0.100 | – |
| 41 | Melonal | 0.019 | 0.025 | – |
| 42 | Isoamyl butyrate | 0.018 | 0.011 | 0.005 |
| 43 | Pineapple furanone | trace | trace | – |
| 44 | Butyl 2-methylbutyrate | – | – | – |
| 45 | Pentyl butyrate | 0.022 | – | 0.009 |
| 46 | Isoamyl isovalerate | 0.046 | trace | trace |
| 47 | Methyl benzoate | trace | – | – |
| 48 | Ethyl heptanoate | trace | – | – |
| 49 | Phenylethanol | trace | – | – |
| 50 | Linalool | 0.036 | – | – |
| 51 | Maltol | trace | 0.086 | 0.046 |
| 52 | Menthone | ! | – | – |
| 53 | Dihydrocarvone | trace | – | – |
| 54 | Benzyl acetate | 0.001 | trace | – |
| 55 | 6-Methyl-5-hepten-2-one propylene glycol acetal | – | 0.055 | – |
| 56 | Menthol | trace | 0.052 | – |
| 57 | cis-6-Nonen-1-ol | 0.001 | – | – |
| 58 | α-Terpineol | 0.020 | – | – |
| 59 | Ethyl octanoate | trace | – | – |
| 60 | Ethyl maltol | 0.011 | trace | – |
| 61 | β-Citronellol | trace | trace | – |
| 62 | Carvone | trace | – | – |
| 63 | Glycerol | 28.971 | 24.329 | 42.940 |
| 64 | Benzaldehyde propylene glycol acetal | trace | – | – |
| 65 | Ethyl phenylacetate | trace | – | – |
| 66 | Benzoic acid | 0.703 | 2.435 | 1.169 |
| 67 | Anethole | trace | – | – |
| 68 | δ-Octalactone | 0.009 | – | – |
| 69 | WS-23 | 3.798 | 3.789 | 3.086 |
| 70 | Melonal propylene glycol acetal | 0.157 | 0.447 | 0.060 |
| 71 | Melonal diethylene glycol acetal | trace | – | – |
| 72 | Menthone propylene glycol acetal | 0.012 | – | – |
| 73 | o-Aminobenzoic acid methyl ester | trace | – | – |
| 74 | Nicotine | 3.373 | 6.580 | 2.537 |
| 75 | Glycerol triacetate (triacetin) | 1.163 | 0.012 | 1.025 |
| 76 | 5-Hydroxy-octanoic acid ethyl ester | – | – | – |
| 77 | Methyl cinnamate | 0.053 | – | 0.035 |
| 78 | Ethyl decanoate | trace | – | – |
| 79 | Vanillin | trace | trace | 0.021 |
| 80 | β-Dihydrocarvone | trace | – | trace |
| 81 | Myrtenal | trace | – | – |
| 82 | Ethyl cinnamate | trace | – | – |
| 83 | γ-Decalactone | 0.031 | – | 0.049 |
| 84 | δ-Decalactone | trace | – | – |
| 85 | Hydroxycitronellal propylene glycol acetal | trace | – | ! |
| 86 | Nerolidol | 0.029 | trace | trace |
| 87 | γ-Dodecalactone | – | – | – |
| 88 | Ethyl laurate | ! | – | – |
| 89 | 5-Hydroxydecanoic acid propylene glycol ester | trace | – | ! |
| 90 | Mesmin | trace | – | ! |
| 91 | β-Ionone | trace | – | – |
| 92 | WS-3 | 0.282 | 0.340 | – |
| 93 | Dihydrojasmonate methyl ester | 0.007 | 0.073 | 0.008 |
| 94 | γ-Dodecalactone | – | – | – |
| 95 | Vanillin propylene glycol acetal | 0.001 | – | – |
| 96 | Benzyl benzoate | 0.038 | trace | 0.312 |
| 97 | Dihydrojasmonate propylene glycol acetal | trace | trace | – |
| 98 | 5-Hydroxydecanoic acid propylene glycol ester | trace | – | ! |
| 99 | Vanillin glycerol acetal | ! | trace | – |
| Total | 99.907 | 99.965 | 99.999 |
Unique components in Sample A (including trace amounts) included: propyl acetate, methyl 2-methylbutyrate, hexanol, ethyl hexanoate, α-terpineol, δ-octalactone, menthone propylene glycol ketal, etc., totaling 29. Sample B's unique components included: ethyl acetoacetate, hexanoic acid, benzyl alcohol, β-myrcene, 6-methyl-5-hepten-2-ol, pineapple furanone, maltol, etc., totaling 15, with higher contents of ethyl acetoacetate and benzyl alcohol. Sample C had 6 unique components, such as isobutanol, acetaldehyde diethyl acetal, phenylethanol, and β-ionone. Thus, while the total volatile substance amounts were similar, the types and compositions varied significantly.
In Sample A, 13 volatile components exceeded 0.1% content, summing to 99.209% of the total peak area. The top 8 by content were: propylene glycol, glycerol, WS-23, nicotine, benzoic acid, isobutyl acetate, leaf alcohol, and isoamyl acetate. In Sample B, 15 components exceeded 0.1%, summing to 99.532%, with the top 8: glycerol, propylene glycol, ethanol, WS-23, nicotine, benzoic acid, triacetin, and benzyl alcohol. In Sample C, 18 components exceeded 0.1%, summing to 99.614%, with the top 8: propylene glycol, glycerol, ethanol, nicotine, WS-23, benzoic acid, isobutyl acetate, and triacetin.
2.3 Sensory Evaluation Analysis of Three Watermelon-Flavored Vape.
The sensory quality evaluation team consisted of experienced evaluators from Shenzhen Boton Flavor Co., Ltd.'s e-cigarette panel. Evaluation results are presented in Table 2.
Table 2. Sensory Evaluation of Different Brands of Watermelon-Flavored Vape
| Sample | Evaluation Score | Evaluation Results |
|---|---|---|
| A | 55.9 | Mild vapor, comfortable sweetness, with fresh watermelon flavor |
| B | 55.3 | Clear and sweet watermelon taste, full vapor, good coordination, acceptable aftertaste |
| C | 52.0 | Clear watermelon aroma, medium taste, average coordination, slight off-notes |
Sample A scored highest, followed by B and C. This may be due to Sample A having the most volatile components (nearly 80), enriching the flavor profile and layering the vaping experience. Alternatively, Sample A's 29 unique components enhanced the overall quality through synergistic effects.
Sensory radar charts for the three watermelon-flavored e-liquids are shown in Figure 2.
Figure 2 indicates minor differences in throat hit, aftertaste, and off-notes, with the most significant variations in irritation and sweetness. Irritation scores were A > B > C, and sweetness scores were B > A > C. Combined with Table 2, Sample C's lower score may stem from reduced sweetness and slight off-notes. Concentration also varied notably (B > A > C), possibly due to Sample B's highest total volatile content, resulting in fuller vapor. Samples A and B had similar sensory profiles, while Sample C scored lower across all indicators, likely due to fewer components leading to a simpler, less coordinated flavor.
Analysis of components exceeding 0.1% content revealed the main framework of watermelon-flavored vape: glycerol, propylene glycol, nicotine, benzoic acid, and WS-23. These five summed to 88.691%, 91.001%, and 81.256% in the samples. E-liquids typically include glycerol, propylene glycol, flavorants, and nicotine, where propylene glycol and glycerol serve as humectants and solvents. Nicotine levels are critical for vaping satisfaction: too low fails to meet user needs, too high may cause discomfort. All samples contained WS-23, a novel cooling agent with fresh, long-lasting, non-bitter, non-irritating, low-dosage properties.
Research on watermelon flavor is less extensive than other fruits. Yang Fan et al.used GC-O-MS with olfactometry, odor dilution factors, and aroma activity values to identify key odorants in heat-treated watermelon juice: (E)-2-heptenal, 6-methyl-5-hepten-2-one, decanal, acetophenone, etc. He Congcong et al.found few esters in watermelon juice via GC-MS, consistent with this study, and identified key components for seedless watermelon aroma: hexanal, (E)-2-nonenal, 6-methyl-5-hepten-2-one, (E)-6-nonenal, (E)-2,6-nonadienal, (Z)-2,6-nonadienal, etc. Hexanal imparts grassy notes, 6-methyl-5-hepten-2-one offers fresh lemon and watermelon scents, and (E)-6-nonenal and (E)-2-nonenal provide pleasant sweet melon aromas. C9 alcohols, aldehydes, and enals like (E)-2-nonenal, (E,Z)-3,6-nonadien-1-ol, and (Z)-6-nonenal contribute to melon and cucumber-like aromas, with unsaturated aldehydes influencing fresh and melon notes. Huang Qinyi et al.used SPME-GC-MS to identify major volatiles in ripe watermelon: palmitic acid, dibutyl maleate, cedrene, and 2,6-di-tert-butyl-p-cresol, none detected here, possibly as they occur in natural plants and daily chemical/food essences—further research is needed. Andy noted (E,Z)-3,6-nonadienal as potentially key for watermelon's unique aroma but prone to decomposition, limiting synthetic flavor production and leaving room for improvement in watermelon-flavored products. Thus, the preliminary replication formula included flavor components like 6-methyl-5-hepten-2-one, hexanal, melon aldehyde, (E)-2-(Z)-6-nonadienol, (E)-2-(Z)-6-nonadienal, (Z)-6-nonenal, and base components like ethanol, propylene glycol, and glycerol.
Combining component analysis and sensory evaluation of the three e-liquids, an initial formula was proposed. E-liquid was prepared based on the base formula, optimized through repeated vaping and adjustments to achieve harmonious aroma. After multiple trials and sensory assessments, the optimal replication formula was determined, as shown in Table 3.
Table 3 Optimized formula of imitation smoke liquid
| Ingredient | Mass Fraction (%) | Flavor Note | Subtotal (%) |
|---|---|---|---|
| 10% Acetic Acid | 0.23 | Acidic Note | 0.23 |
| 1% Ethyl Acetate | 0.20 | ||
| 10% Ethyl Propionate | 0.15 | ||
| 10% Isobutyl Acetate | 0.15 | ||
| 1% Ethyl 2-Methylbutyrate | 1.00 | ||
| Isoamyl Butyrate | 0.10 | ||
| Isoamyl Acetate | 0.10 | Fruity Note | 9.20 |
| 0% Isoamyl-2-Methylbutyrate | 1.00 | ||
| 1% Limonene | 0.80 | ||
| 1% Ethyl trans-2-Hexenoate | 0.50 | ||
| Isoamyl Butyrate | 0.10 | ||
| 10% Watermelon Ketone | 5.00 | ||
| Decanal | 0.10 | ||
| 10% Hexyl Butyrate | 0.15 | ||
| Leaf Alcohol | 0.20 | ||
| 10% Leaf Acetate | 0.15 | ||
| 1% Hexyl Acetate | 1.00 | ||
| 1% Melonal | 0.75 | ||
| Dihydrojasmonate | 0.65 | Green Note | 4.57 |
| Hexanal | 0.35 | ||
| 10% trans-2-cis-6-Nonadienol | 0.06 | ||
| 10% trans-2-cis-6-Nonadienal | 0.06 | ||
| cis-6-Nonenal | 0.65 | ||
| 10% Nonanal | 0.55 | ||
| Benzoic Acid | 0.55 | Roasted Note | 0.55 |
| 6-Methyl-5-Hepten-2-one | 2.00 | ||
| Pyrazine | 2.80 | Smoky Note | 4.80 |
| WS-23 | 3.00 | Cooling Note | 3.00 |
| Qinfeng Aldehyde* | 0.65 | Fresh Note | 0.65 |
| Ethanol | 30.00 | Solvent | 30.00 |
| Glycerin | 40.00 | Solvent | 77.00 |
| Propylene Glycol | 7.00 |
Table 3 indicates the replicated e-liquid comprises 32 raw materials, mostly synthetic flavors, reducing production costs. Flavor proportions are: fruity notes 9.20%, green notes 4.57%, cooling notes 3.00%, fresh notes 0.65%, roasted notes 0.55%, sour notes 0.23%, solvents 77.00%, and nicotine benzoate salt 4.80%. Vaping evaluation found it closely resembles watermelon characteristics: top notes of intense watermelon ice with banana and pineapple tropical fruit hints, base notes of refreshing watermelon rind, body notes thick and layered, overall coordinated with lingering effects. The total ion chromatogram of the replicated e-liquid's volatile components is shown in Figure 3.
This study employed direct injection and GC-MS to analyze volatile components in three popular market watermelon-flavored e-liquids, detecting 99 aroma-contributing components, primarily glycerol, propylene glycol, nicotine, and flavorants. The samples shared 28 components, with notable differences in solvents, isobutyl acetate, ethyl butyrate, isoamyl acetate, and cooling agents. By integrating component analysis with flavor replication techniques, a novel watermelon-flavored e-liquid was successfully developed, featuring fresh watermelon flavor, layered body aroma, natural and refreshing scent, coordinated style, and lingering effects. This provides a reference for developing and replicating fresh fruit-flavored e-liquids for Vape.
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