Parameters of HS–SPME
SPME offers a rapid, solvent-free method for the extraction of organic compounds from aqueous samples. It has been pointed out that some SPME applications demonstrate a bias for extracting higher boiling-point compounds over lower boiling-point compounds, and the extracts will not be representative of the gas phase at equilibrium as it is perceived by the nose. However, by the optimization of SPME variables (choice of fibre, thickness of the fibre phase, length of exposure, salt addition, extraction temperature and time, etc.), it was possible to obtain representative and reproducible HS–SPME extracts of the typical odour of flavour foods.[7,10,11]
The presence of salts has been shown to improve the adsorption of analytes for SPME analyses[16,17] because the dissociated ions disrupt the sample matrix by decreasing the solubility of the aroma molecules, which then are more readily absorbed by the headspace fibre. The same phenomenon has also been found in the absorption of volatiles in cherry by SPME phases. For this study, all samples were prepared with saturated sodium chloride, and it was observed that the addition of salt significantly improved the extraction efficiency of most volatiles, especially the acids (acetic acid, 3-methylbutanoic acid, etc.) and some highly volatile components (acetaldehyde and ethyl acetate). In contrast, the presence of sodium chloride slightly decreased the extraction efficiency for limonene and geranylacetone (data not shown). This phenomenon is probably due to competitive absorption of the SPME fibre.
In the current investigation, several SPME variables were studied, including SPME fibre, temperature and time of extraction. Three fibres, coated with 50/30 µm DVB/CAR/PDMS, 75 µm CAR/PDMS and 100 µm PDMS, were evaluated for the extraction of aroma-active compounds in cherry. PDMS fibres exhibited greater extraction of non-polar compounds (aldehydes and esters) than mixed fibres. PDMS/DVB and CAR/DVB/PDMS fibres extracted a similar proportion of volatile compounds; however, DVB/CAR/PDMS fibre extracted more polar and middle polar compounds in cherry, such as acetic acid, 3-methyl butanoic acid and pentanoic acid, and it has been used for the analysis of aroma compounds in apple and longan.
To select the optimum extraction temperature and time, a 50/30 µm CAR/DVB/PDMS fibre was used. Extraction was carried out at 30°C, 40°C, 50°C and 60°C for 10, 20, 30, 40, and 50 min. Figure 1 shows the result in graphic form, expressed as the sum of areas of all the volatile compounds obtained from cherry by use of each set of conditions. The best result was obtained at 50°C for 40 min.
Identification of Compounds
GC–MS was used for the determination of volatile compounds present in the extracts. A majority of compounds were identified by comparison of their spectra with those recorded in the Wiley 275.L database. Meanwhile, the RIs of unknown compounds were calculated using GC retention index standards (hydrocarbons from straight-chain, C7–C30) compared with the RIs of the standards or those reported in published work.[21,22] The data in Table 1 show that a total of 52 compounds were identified in five cherries on the DB-Wax and DB-5 columns. Most compounds have been reported previously in cherry[3,5,23] and consisted largely of 18 alcohols, 16 aldehydes, six acids, six esters, four terpenes, one ketone and one furan. ‘Stella’ showed the richest composition, with 48 compounds. ‘Lapins’, ‘Hongdeng’, and ‘Zhifuhong’ had a moderate composition, with 46, 41 and 44 compounds, respectively; ‘Rainier’ gave the simplest mixture, with only 36 identified compounds.
Table 1. The volatile compounds in five cherry fruits identified by GC–MS analysis on DB-Wax and DB-5 columns
|RI (DB-Wax)||RI (DB-5)||Compounds||Identification*||Relative peak area **|
|Aldehydes|| || || ||50.55 (1.63)d||18.20 (1.56)b||25.19 (1.73)c||46.45 (0.95)d||9.11 (0.44)a|
|<900||<700||Acetaldehyde||RI, MS||0.34 (0.14)bc||0.23 (0.14)ab||0.17 (0.03)a||0.11 (0.11)a||0.43 (0.13)c|
|<900||<700||2-Methylpropanal||RI, MS||0.11 (0.01)b||0.03 (0.01)a||ND||0.06 (0.03)ab||0.24 (0.05)c|
|971||703||3-Methylbutanal||RI, MS||0.65 (0.08)b||ND||ND||0.81 (0.04)b||0.25 (0.01)a|
|1073||804||Hexanal||RI, MS||19.71 (1.54)b||1.55 (0.76)a||1.79 (0.22)a||21.00 (1.00)b||3.59 (0.27)a|
|1136||817||(Z)-3-Hexenal||RIL, MS||0.24 (0.05)a||0.28 (0.04)ab||0.38 (0.03)ab||0.43 (0.04)c||0.29 (0.04)bc|
|1192||843||(Z)-2-Hexenal||RIL, MS||0.17 (0.02)c||0.10 (0.01)ab||0.12 (0.01)b||0.08 (0.01)a||0.10 (0.01)ab|
|1211||861||(E)-2-Hexenal||RI, MS||2.92 (0.16)bc||1.07 (0.06)a||3.35 (0.25)c||6.81 (0.77)d||1.68 (0.08)ab|
|1282||1006||Octanal||RI, MS||0.71 (0.13)b||ND||0.23 (0.05)a||0.60 (0.04)b||0.16 (0.02)a|
|1333||962||(E)-2-Heptenal||RIL[29,30], MS||0.43 (0.12)b||ND||ND||0.38 (0.00)a||ND|
|1383||1110||Nonanal||RI, MS||2.25 (0.11)d||0.18 (0.02)a||0.53 (0.06)b||1.91 (0.06)c||0.43 (0.02)ab|
|1417||1071||(E)-2-Octenal||RIL[29,30], MS||2.77 (0.04)c||ND||0.03 (0.01)a||1.76 (0.04)b||ND|
|1488||1210||Decanal||RI, MS||0.07 (0.01)c||ND||0.10 (0.02)c||0.03 (0.01)a||0.04 (0.01)ab|
|1517||965||Benzaldehyde||RI, MS||17.74 (0.62)c||13.50 (0.80)bc||16.77 (1.56)bc||11.03 (0.84)b||2.18 (0.20)a|
|1569||1121||(E,Z)-2,6-Nonadienal||RI, MS||ND||ND||0.37 (0.03)b||ND||0.22 (0.03)a|
|1620||1047||β-Phenylacetaldehyde||RI, MS||0.57 (0.00)d||ND||0.22 (0.01)b||0.30 (0.04)c||0.09 (0.01)a|
|1697||1305||(E,E)-2,4-Nonadienal||RIL, MS||0.27 (0.01)c||ND||0.13 (0.00)a||0.22 (0.01)b||ND|
|Esters|| || || ||0.98 (0.14)a||2.32 (0.21)c||1.52 (0.04)b||1.24 (0.09)ab||1.11 (0.04)ab|
|<900||<700||Ethyl acetate||RI, MS||ND||0.06 (0.02)a||0.04 (0.00)a||0.07 (0.01)a||0.45 (0.04)b|
|1023||808||Ethyl butanoate||RI, MS||ND||0.18 (0.03)b||0.05 (0.02)a||0.34 (0.02)c||ND|
|1232||1001||Ethyl hexanoate||RI, MS||0.08 (0.01)a||0.10 (0.01)b||0.03 (0.01)ab||0.07 (0.01)ab||0.09 (0.03)b|
|1320||1013||Hex-2-enyl acetate||RIL, MS||0.18 (0.01)b||ND||0.23 (0.04)b||0.19 (0.03)b||0.08 (0.00)a|
|1771||1192||Methyl salicylate||RI, MS||0.48 (0.06)b||0.52 (0.03)b||0.58 (0.03)b||0.22 (0.03)a||0.27 (0.02)a|
|2253||1999||Ethyl hexadecanoate||RI, MS||0.24 (0.06)a||1.47 (0.16)b||0.58 (0.14)a||0.34 (0.04)a||0.22 (0.01)a|
|Alcohols|| || || ||59.09 (0.44)b||110.83 (3.97)e||97.41 (1.34)d||72.06 (2.44)c||49.84 (1.07)a|
|1116||701||2-Pentanol||RIL[29,31], MS||0.06 (0.01)a||ND||ND||0.36 (0.04)c||0.26 (0.02)b|
|1118||715||3-Pentanol||RIL[29,32], MS||0.15 (0.01)a||ND||ND||0.29 (0.03)b||0.35 (0.04)b|
|1156||670||1-Butanol||RI, MS||0.54 (0.01)b||ND||0.05 (0.01)a||2.01 (0.13)c||2.43 (0.11)d|
|1208||738||3-Methylbutanol||RI, MS||ND||1.17 (0.21)b||ND||ND||0.04 (0.01)a|
|1245||752||3-Methyl-3-buten-1-ol||RIL, MS||0.40 (0.09)a||1.37 (0.14)c||0.88 (0.14)b||0.68 (0.08)ab||0.44 (0.07)ab|
|1249||765||1-Pentanol||RI, MS||0.39 (0.01)c||0.09 (0.00)a||0.13 (0.01)a||0.26 (0.02)b||0.14 (0.02)a|
|1316||770||3-Methyl-2-buten-1-ol||RIL[31,32], MS||0.81 (0.03)b||1.62 (0.08)d||1.39 (0.09)c||1.81 (0.04)d||0.49 (0.02)a|
|1358||870||1-Hexanol||RI, MS||2.75 (0.21)ab||2.22 (0.05)a||3.36 (0.27)b||2.55 (0.11)a||2.86 (0.09)ab|
|1373||862||(Z)-3-Hexen-1-ol||RI, MS||0.28 (0.02)a||0.35 (0.04)a||0.31 (0.04)a||0.48 (0.08)a||0.68 (0.03)b|
|1405||882||(E)-2-Hexen-1-ol||RIL, MS||21.15 (1.39)b||16.29 (0.53)a||25.05 (1.38)b||22.75 (0.65)b||16.25 (0.49)a|
|1441||975||1-Octen-3-ol||RI, MS||0.52 (0.05)d||0.36 (0.06)c||0.13 (0.01)a||0.23 (0.02)bc||ND|
|1445||960||1-Heptanol||RI, MS||0.33 (0.03)c||0.15 (0.02)ab||0.16 (0.02)ab||0.18 (0.01)b||0.10 (0.01)a|
|1558||1076||1-Octanol||RI, MS||0.76 (0.09)c||0.13 (0.02)a||ND||0.32 (0.04)b||2.15 (0.06)d|
|1653||1165||1-Nonanol||RI, MS||0.54 (0.05)b||0.28 (0.00)a||0.47 (0.06)b||0.26 (0.03)a||0.25 (0.02)a|
|1794||1069||α-Phenethyl alcohol||RI, MS||ND||ND||ND||ND||0.15 (0.03)|
|1860||1041||Benzyl alcohol||RI, MS||28.86 (1.89)ab||82.84 (3.98)d||63.35 (2.79)c||37.88 (2.01)b||23.62 (0.78)a|
|1896||1116||β-Phenylethyl alcohol||RI, MS||0.71 (0.06)a||2.25 (0.11)c||1.37 (0.03)b||0.73 (0.12)a||0.81 (0.06)a|
|1957||1463||1-Dodecanol||RI, MS||0.85 (0.04)a||1.71 (0.15)c||0.75 (0.07)a||1.29 (0.11)b||0.97 (0.08)ab|
|Terpenes|| || || ||1.48 (0.07)a||0.86 (0.06)a||2.31 (0.31)b||0.79 (0.11)a||1.36 (0.14)a|
|1169||1036||Limonene||RI, MS||ND||0.03 (0.01)a||0.05 (0.01)b||0.03 (0.00)a||0.10 (0.01)c|
|1551||1106||Linalool||RI, MS||0.48 (0.11)bc||ND||0.51 (0.06)c||0.22 (0.04)a||0.24 (0.04)ab|
|1633||1157||Menthol||RI, MS||0.20 (0.02)a||ND||0.48 (0.08)b||ND||0.27 (0.01)a|
|1856||1447||Geranylacetone||RI, MS||0.79 (0.03)a||0.83 (0.05)ab||1.27 (0.15)b||0.54 (0.15)a||0.75 (0.10)a|
|Furans|| || || ||0.74 (0.02)b||ND||ND||0.30 (0.07)a||ND|
|1275||995||2-Pentylfuran||RIL, MS||0.74 (0.02)b||ND||ND||0.30 (0.07)a||ND|
|Ketones|| || || ||1.56 (0.06)c||0.46 (0.08)a||1.47 (0.16)c||1.37 (0.06)c||0.92 (0.06)b|
|1324||988||6-Methyl-5-hepten-2-one||RI, MS||1.56 (0.06)c||0.46 (0.08)a||1.47 (0.16)c||1.37 (0.06)c||0.92 (0.06)b|
|Acids|| || || ||6.42 (0.53)d||5.84 (0.19)cd||3.30 (0.20)b||4.89 (0.26)c||1.90 (0.19)a|
|1435||<700||Acetic acid||RI, MS||0.02 (0.00)a||0.04 (0.01)a||0.02 (0.01)a||0.03 (0.01)a||0.05 (0.00)b|
|1660||839||3-Methylbutanoic acid||RI, MS||0.41 (0.02)a||1.88 (0.14)d||1.11 (0.10)c||0.81 (0.06)bc||0.59 (0.08)ab|
|1728||922||Pentanoic acid||RI, MS||0.13 (0.04)b||0.08 (0.00)a||ND||0.1 (0.02)b||ND|
|1840||984||Hexanoic acid||RI, MS||4.22 (0.31)b||1.22 (0.07)c||0.21 (0.08)a||2.90 (0.29)d||0.31 (0.04)a|
|2051||1176||Octanoic acid||RI, MS||0.74 (0.01)b||1.05 (0.10)c||0.76 (0.03)b||0.42 (0.04)a||0.46 (0.04)a|
|2264||1374||Decanoic acid||RI, MS||0.90 (0.15)ab||1.57 (0.07)c||1.20 (0.15)b||0.58 (0.09)a||0.49 (0.03)a|
According to the results of the quantitative analyses, aldedydes and alcohols had higher peak areas in five cherry fruits (over 80% of total volatiles), then followed the acids, esters and terpenes. The most represented class of compounds in all five cherries was C6 compounds and aromatic compounds, according to their relative peak areas, i.e. hexanal (1.55–21.00), (E)-2-hexenal (1.07–6.81), 1-hexanol (2.22–3.65), (E)-2-hexen-1-ol (16.25–25.05), benzaldehyde (2.18–17.74) and benzyl alcohol (23.62–82.84). The highest content of hexanal and (E)-2-hexenal was present in ‘Stella’, whereas the lowest content was found in ‘Rainier’. 1-Hexanol and (E)-2-hexen-1-ol had the highest content in ‘Hongdeng’. The result was similar to the previous report about sweet cherry ‘Hongdeng’ by Zhang et al.. C6 compounds are known to have a characteristic ‘green leaf’ odour, as released from green plant tissue following mechanical damage. As for benzaldehyde (almond-like odour) and benzyl alcohol (floral odour), they had the largest relative peak areas, in ‘Lapins’ and ‘Rainier’, respectively.
In addition, two ketones (geranylacetone and 6-methyl-5-hepten-2-one) were found with higher relative peak areas (0.54–1.27 and 0.46–1.56, respectively) in the five cherries. 6-Methyl-5-hepten-2-one has been found previously in some sweet cherry cultivars,[4,23] such as ‘Lapins’, ‘Stella’, ‘Ambrunes’ and ‘Pico Colorado’, and geranylacetone has been reported in Monastrell and Cabernet Gernischt grapes.[25,26] It is worth noticing that geranylacetone identified in the present investigation has not been reported in other studies about cherries.
Statistically significant differences were found between the average content of most compounds in the five cultivars by ANOVA and Duncan's multiple range test (Table 1). The most important compounds in differentiating samples were the total alcohols and β-phenylacetaldehyde.
GC–O Dilution Analysis
The GC–O dilution analysis was performed by successively diluting the cherry samples with distilled water. The concentrations of compounds extracted by SPME fibre had a better linear relationship with the dilutions at lower concentration, which had been evaluated by Deibler[6,7], Fan and Choi.
To ensure that the results of GC–O dilution analysis were reliable, a linear relationship was drawn between the concentration of extracted compounds by SPME fibre and the dilutions. ‘Hongdeng’ juice was sequentially diluted at a 1:1 ratio with distilled water, and the responses (total ion abundance) for several alcohols, aldehydes, acids and esters were evaluated. The results showed that 1-hexanol, (E)-2-hexen-1-ol, benzyl aclcohol, hexanal, (E)-2-hexenal, benzaldelyde, ethyl hexanoate, linalool and hexanoic acid had adequate linearity for GC–O dilution analysis (Figure 2), since their linear correlation coefficients (R2) were all > 0.92. Among these, 1-hexanol generated the best correlation (R2 = 0.9918).
Figure 2. Linearity of alcohols, aldehydes, acids and esters from ‘Hongdeng’ cherry juice extracted by HS–SPME (DVB/CAR/PDMS fibre) and detected on a DB-wax column using a series of 1:1 dilutions; the first dilution was assigned a number of 10. (A) 1-Hexanol, (E)-2-hexen-1-ol and benzyl aclcohol; (B) hexanal, (E)-2-hexenal and benzaldelyde; (C) ethyl hexanoate, linalool and hexanoic acid
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Before GC–O dilution analysis, a direct GC–O technique was performed to make a comparison of SPME extracted odour with fresh cherry juice. Judging by the evaluation results of two assessors, the desorbed odour by GC from SPME was quite similar to that of the reference juice. In the meantime, ‘cooked’ odour was perceived in the juice at the first time of dilution, but this unpleasant odour gradually decreased along with sequential dilutions, and was hardly perceived by the fourth dilution.
On the basis of the FD values on a DB-Wax column (Table 2), a total of 40 aroma-active compounds were detected in the five cherries. The potentially important compounds were hexanal, (Z)-3-hexenal, (E)-2-hexenal, nonanal and geranylacetone (FD ≥ 16) in all five cherries. These compounds impart green, orange and floral odours, respectively. Hexanal and (E)-2-hexenal, as the important aroma compounds in sweet cherry fruits, have been reported previously.[4,5,23]
Table 2. Potent aroma compounds detected by HS–SPME and GC–O dilution analysis on a DB-Wax column
|RI (DB-Wax)||Compounds||Descriptor||FD factors*|
C6 compounds seemed to be the most important aroma compounds in cherry. Hexanal, (E)-2-hexenal and (Z)-3-hexenal showed higher FD factors (FD ≥ 16) in all five cherry cultivars, whereas 1-hexanol, (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol exhibited medium FD factors (FD ≥ 8). Compared to ‘Lapins’, ‘Rainier’, ‘Hongdeng’ and ‘Zhifuhong’, 1-hexanol (floral and grape odour) had the highest FD factor (FD = 16) in ‘Stella’. (Z)-2-Hexenal and hexanoic acid were detected in all samples with lower FD factors. They present green, acidic aromas. These C6 alcohols and aldehydes arise from the consecutive action of the lipoxygenase and alcohol deshydrogenase enzymes on polyunsaturated fatty acids.
Nonanal had higher FD factors in ‘Stella’ and ‘Zhifuhong’ (FD ≥ 64) but lower values (FD = 16) in ‘Rainier’. Benzaldehyde and β-phenylacetaldehyde (FD = 32 and 16, respectively) was probably important to ‘Lapins’, ‘Hongdeng’ and ‘Stella’, giving almond and floral aroma, respectively. Mattheis et al. have reported relatively high concentrations of benzaldehyde in Prunus avium ‘Bing’. Girard and Kopp have also found the importance of benzaldehyde by research on 12 sweet cherries. Acetaldehyde, octanal and decanal had moderate FD factors (FD ≥ 4) in five cherries. Octanal (lemon-like odour) and decanal (grassy odour) can be perceived easily because of their low olfactory thresholds.
2-Methylpropanal, 3-methylbutanal, (E)-2-octenal, (E,Z)-2,6-nonadienal and (E,E)-2,4-nonadienal had greater differences in FD factor in the five cherries. 2-Methylpropanal could be very important to ‘Zhifuhong’ (FD = 16), whereas its FD factor was only 2 in ‘Hongdeng’. 3-Methylbutanal had the highest FD factor (FD = 16) in ‘Lapins’ and ‘Stella’; however, it was not detected in ‘Rainier’ and ‘Hongdeng’. (E)-2-Octenal could be a potential aroma-active compound (FD = 16) in ‘Lapins’, but was not found in ‘Zhifuhong’. (E,Z)-2,6-nonadienal and (E,E)-2,4-nonadienal, giving cucumber and fatty aromas, respectively, have lower threshold levels (0.02 and 0.06 ppb, respectively, in water). (E,Z)-2,6-Nonadienal had a higher FD factor (FD ≥ 16) in ‘Hongdeng’ and ‘Zhifuhong’, whereas (E,E)-2,4-nonadienal could be important in ‘Lapins’ and ‘Stella’ (FD = 16).
Benzyl alcohol (floral aroma) and β-phenylethyl alcohol (rosy aroma) were identified as potentially important aroma compounds in the five cherries, based on their AEDA values (FD ≥ 8). 1-Octen-3-ol, with a mushroom odour, contributed to the aroma (FD ≥ 8) in ‘Lapins’, ‘Rainier’, ‘Stella’ and ‘Hongdeng’. 1-Octanol was detected in all five cherry cultivars; it had lower FD factors and gave a fruity aroma. 1-Butanol was found in ‘Lapins’, ‘Rainier’ and ‘Zhifuhong’ with low FD factors (FD ≤ 4).
Several esters were detected in the five cherries. Among them, methyl salicylate, which generates a wintergreen odour, had a higher FD factor (FD ≥ 8) in the five cherries. Ethyl hexanoate exhibited potential importance in ‘Lapins’, ‘Rainier’, ‘Stella’ and ‘Hongdeng’, based on its FD factor (FD = 8). Ethyl acetate had the highest FD factor (FD = 8) in ‘Zhifuhong’, whereas hex-2-enyl acetate could be more important in ‘Stella’ (FD = 8).
As for the determination of acids, a total of four acids were detected by means of GC–O, acetic, 3-methylbutanoic, hexanoic and octanoic acids. 3-Methylbutanoic acid seemed to be the most significant acid in the five cherries (FD ≥ 8). Hexanoic acid had a moderate FD factor (FD = 8) in ‘Stella’. Generally, the contribution of acetic acid and octanoic acid to cherry aroma may be limited (FD ≤ 4), because their thresholds are quite high.
Four terpenes, limonene, linalool, menthol and geranylacetone, were detected in the five cherries. Among them, linalool, menthol and geranylacetone were common to all five samples, but limonene was absent from ‘Lapins’. Linalool, presenting as a citrusy aroma, seems to be an important odorant (FD = 16) in four cherries, with the exception of ‘Rainier’ (FD = 4). Menthol had middle FD factors (FD = 8) in ‘Lapins’, ‘Hongdeng’ and ‘Zhifuhong’, giving a minty aroma.
To sum up the results, the most significant aroma compounds in ‘Lapins’ were hexanal (FD ≥ 64); (E)-2-hexenal, nonanal and benzaldehyde (FD = 32); acetaldehyde, 3-methylbutanal, (Z)-3-hexenal, octanal, (E)-2-octenal, decanal, β-phenylacetaldehyde, (E,E)-2,4-nonadienal, methyl salicylate, (Z)-3-hexen-1-ol, 1-octen-3-ol, benzyl alcohol, linalool, and geranylacetone (FD = 16). In ‘Rainier’, hexanal and (E)-2-hexenal (FD = 32); (Z)-3-hexenal, nonanal, benzaldehyde, (Z)-3-hexen-1-ol, benzyl alcohol and geranylacetone (FD = 16) were determined as the most important odour-active volatiles. In ‘Hongdeng’, the most significant aroma compounds identified on the DB-Wax column involved hexanal, (E)-2-hexenal, nonanal, benzaldehyde and geranylacetone (FD = 32); (Z)-3-hexenal, (E,Z)-2,6-nonadienal, β-phenylacetaldehyde, benzyl alcohol, β-phenylethyl alcohol, linalool, and 3-methylbutanoic acid (FD = 16). In ‘Stella’, hexanal, (E)-2-hexenal and nonanal (FD ≥ 64); (Z)-3-hexenal and benzaldehyde (FD = 32); 3-methylbutanal, octanal, β-phenylacetaldehyde, (E,E)-2,4-nonadienal, 1-hexanol, (Z)-3-hexen-1-ol, 1-octen-3-ol, linalool and geranylacetone (FD=16) were found to contribute greatly to the aroma profile. Finally, in ‘Zhifuhong’, nonanal (FD ≥ 64); hexanal, (E)-2-hexenal, (E,Z)-2,6-nonadienal and geranylacetone (FD = 32); acetaldehyde, 2-methylpropanal, (Z)-3-hexenal, decanal, methyl salicylate benzyl alcohol and linalool (FD = 16) were determined as the most important odour-active volatiles.
In the present study, HS–SPME using DVB/CAR/PDMS fibre was employed to extract the volatiles in ‘Lapins’, ‘Rainier’, ‘Stella’, ‘Hongdeng’ and ‘Zhifuhong’. A total of 52 compounds were identified in five cherries on DB-wax and DB-5 columns. Of these, hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexen-1-ol, benzaldehyde and benzyl alcohol were the main volatile compounds, according to their high comcentrations in five cherries.
A combination of HS–SPME and GC–O dilution analysis techniques provided a satisfactory assessment of the most volatile compounds that play a major role in odour perception. Hexanal, (E)-2-hexenal, (Z)-3-hexenal, nonanal, geranylacetone, benzaldehyde and benzyl alcohol were the most important aroma-active compounds in all five cherry samples. In addition, acetaldehyde, 3-methylbutanal, octanal, (E)-2-octenal, (Z)-3-hexen-1-ol, decanal, β-phenylacetaldehyde, (E,E)-2,4-nonadienal, methyl salicylate, 1-octen-3-ol, linalool and (E,Z)-2,6-nonadienal were also the important aroma compounds in certain cherry cultivars. From the present results, it was concluded that the aroma profiles were similar in the five cherry cultivars, but significant variations were found in the contributions of these compounds to each cherry. In future investigations, quantitative analysis and sensory work are needed to further characterize the differences between these cherry cultivars.