Characterization of the Major Odor-Active Compounds in Dry Jujube

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Chemistry and Biology of Aroma and Taste

Characterization of the Major Odor-active Compounds in Dry Jujubes Cultivars by Application of Gas Chromatography-Olfactometry and Odor Activity Value Zuobing Xiao, and Jiancai Zhu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b01366 • Publication Date (Web): 23 May 2018 Downloaded from http://pubs.acs.org on May 23, 2018

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Journal of Agricultural and Food Chemistry

Characterization

of

the

Major

Odor-active

Compounds in Dry Jujubes Cultivars by Application of Gas Chromatography-Olfactometry and Odor Activity Value JianCai Zhu, ZuoBing Xiao* School of Food Science and Technology, Jiangnan University, Wuxi 214122, China *Correspondence author: Xiao Zuobing Address: No.1800, Lihu Avenue, Wuxi City, Jiangsu Province, People’s Republic of China Tel: 0086-0510-85919106 Email: [email protected]

1

ACS Paragon Plus Environment


1

Abstract:

2

The volatile compounds of jujube (Ziziphus jujube Mill.) puree obtained from

3

three cultivars: ‘jinsixiaozao’ (Y1), ‘youzao’ (Y2), and ‘yuzao’ (Y3) were analyzed by

4

gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry,

5

GC-flame photometric detection, and nitrogen phosphorus detector. The results

6

showed that a total of 37, 37, and 35 odor-active compounds were identified by GC-O

7

in samples of Y1, Y2, and Y3, respectively. In addition, the odor activity value (OAV)

8

was used to determine the important compounds. The results demonstrated that

9

hexanal (OAV: 39-85), (E)-2-octenal (OAV: 32-70), β-damascenone (OAV: 14-49),

10

ethyl hexanoate (OAV: 22-39), 3-mercaptohexyl acetate (OAV: 17-24), and

11

2,5-dimethylpyrazine (OAV: 17-22) were key odor-active compounds. It is of great

12

significance to develop high grade jujube food by determining key odor-active

13

compounds. Furthermore, four volatiles (hexanal, 1-octen-3-ol, 3-mercapohexyl

14

acetate, and benzaldehyde) reduced the overall throueshold value by 2.36, 1.01, 1.34,

15

and 1.19, respectively.

16

Keyword: Jujube; GC-O; OAV; Odor-active compounds

2


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17

Introduction

18

Aroma was an important characteristic of food as well as the key indicator for

19

assessing food quality. Tens of thousands of natural aroma volatiles exist and

20

contribute to different food aromas, so it was considered that food aroma was the

21

combination of different aroma volatiles and relative amounts.

22

Amongst those compounds, sulfur compounds, even at trace levels, might

23

contribute to the characteristic aroma of certain fruits because of their extremely low

24

odor

25

4-mercapto-4-methyl-2-pentanone, 3-mercaptohexanol, furfuryl mercaptan and

26

4-mercapto-4-methylpentan-2-ol were 0.0008, 0.055, 0.036 and 0.06 µg/kg,

27

respectively.1, 2 Thus, those compounds might be considered as important contributors

28

to the aroma of fruit. According to previous researches, sulfur compounds were

29

widespread in foods, such as raspberry,2 cheeses,3 ham,4 blueberry,5 grapefruit,6

30

oolong tea,7 and cranberry.8

threshold.

For

example,

the

threshold

values

of

31

Similarly, nitrogenous compounds were readily formed due to the heating caused

32

by Maillard reactions.9 In particular, pyrazine compounds with low odor thresholds

33

had been identified as directly contributing to the roasted aroma, which was

34

widespread in coffee,10 heated beef,11 and soybean.12 Due to their trace levels,

35

quantitation of such compounds was a challenge. Thus, specific detectors were

36

necessary for the assay of those compounds, such as the nitrogen phosphorus detector

37

(NPD).

38

The jujube (Ziziphus jujube Mill.) was rich in carbohydrates, salts, minerals,

39

vitamins, fatty acids, amino acids, and proteins. This high nutritive quality has led to

40

jujubes being widely used in processing industries. Drying of jujube decreased the

41

water activity therein and increased the sugar concentration. Because of this the 3



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42

shelf-life of dry jujubes was high and they were available for use over extended

43

periods of time.13 Recently, many research of jujubes focused on the volatile

44

compounds,14-18 antioxidant properties,19 polyphenol profile,

45

biological properties,21, 22 and pharmacological properties of jujube fruits.13

20

chemical and

46

In the process of storage and processing, the aroma of jujube becomes more

47

abundant. The aroma compounds of jujube could be studied deeply in order to

48

determine the key aroma compounds, especially the sulfur and nitrogenous

49

compounds. It was of great significance to develop high grade jujube food by artificial

50

imitation of jujube flavor.

51

However, few projects entailed the systematic evaluation of odor-active volatile

52

compounds. Besides, less attention has been paid to sulfur and nitrogenous

53

compounds in jujube samples. Therefore, the aims of this research were to identify

54

volatile compounds in jujube puree by gas chromatography-mass spectrometry

55

(GC-MS), flame photometric detection (FPD), and nitrogen phosphorus detector

56

(NPD), and to determine the key aroma compounds.

57

Experimental

58

Chemicals

59

2,3-Butanedione, propanol, butanol, 2,3-pentandione, butyl acetate, hexanal,

60

ethyl pentanoate, heptanal, (E)-2-hexenal, ethyl hexanoate, pentanol,

61

3-hydroxy-2-butanone, (E)-2-heptenal, ethyl heptanoate, 6-methyl-5-hepten-2-one,

62

hexanol, nonanal, (E)-2-octenal, 1-octen-3-ol, ethyl octanoate, furfural, acetic acid,

63

decanal, 2-acetylfuran, benzaldehyde, octanol, 5-methyl-2-furfural, γ-butyrolactone,

64

methyl decanoate, butanoic acid, phenylacetaldehyde, acetophenone, ethyl benzoate,

65

γ-hexalactone, pentanoic acid, ethyl dodecanoate, β-damascenone, phenylmethanol,

66

γ-octalactone, hexanoic acid, ethyl tetradecanoate, 2-ethylphenol, octanoic acid, 4


octanal,

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67

decanoic

acid,

tetradecanoic

68

2,6-dimethylpyrazine, 2-acetyl-1-pyrroline, 2-ethylpyrazine, 2,3,5-trimethylpyrazine,

69

2-methoxy-3,5-dimethylpyrazine,

70

methanethiol, 2-ethyl-3,6-dimethylpyrazine, 2,3,5,6-tetramethylpyrazine, methionol,

71

methional,

72

3-mercaptohexan-1-ol and difurfuryl sulfide, 2-octanol, 2-acetylpyrazine, dipropyl

73

disulfide were purchased from Sigma-Aldrich (Saint Luis, EUA). All of the chemical

74

standards used above were of GC quality.

75

Materials

3-mercapohexyl

acid,

2-methypyrazine,

dimethyl

acetate,

sulfide,

dimethyl

2,5-dimethylpyrazine,

ethanethiol,

tetrasulfide,

methional,

2-acetylthiophene,

76

Ripe samples consisted of three varieties of jujubes (Y1, Z. jujuba Mill. cv.

77

‘jinsixiaozao’, Y2, Z. jujuba Mill. cv. ‘youzao’, and Y3, Z. jujuba Mill. cv. ‘yuzao’),

78

collected from local farm in Cangzhou, Hebei Province, Jiaxian, ShenXi Province and

79

Hetian, Xinjiang Province during the 2016 harvest season. The samples were carefully

80

identified by Dr. Wang Hui of ShangHai Botanical Garden. A mature fruit without

81

any physical damage were selected. A total of 2.5 kg of jujube with initial moisture

82

content of 67.5 % was dried in the electric hot air drying oven for 6 h at 80 °C. The

83

moisture content of jujube dropped to 27.7 %. After that, 1.4 kg of dried jujube saved

84

in dry environment with constant temperature (5 °C) and humidity (30 °C) for one

85

month.

86

Then, 0.5 kg of jujubes were crushed and manually deseeded. After that, the

87

deseeded sample was placed in a juicer with deionised water (400 g). In addition, 30 g

88

sodium chloride solution (20 %) and 20 g sodium fluoride solution (1 %) in Milli-Q

89

deionized water were also added to obtain puree. Then, the puree was immediately

90

employed to the next experiment.

5



Page 6 of 43

91

Headspace-Solid phase microextraction (HS-SPME) absorption of aroma

92

compounds

93

A 75 µm carboxen-poly dimethyl siloxane (CAR-PDMS) fiber was employed in

94

this study. Before extracting jujube puree, the main parameters (extraction time,

95

sample amount, extraction temperature) were investigated. Then, SPME fiber was

96

withdrawn and directly introduced to the GC injector for desorption and analysis. All

97

the experiments were performed in triplicate.

98

Calibration of standard curves

99

To obtain a matrix similar to that of jujube puree, model solution was prepared

100

containing 10 mg/g L(-)-malic acid, 80 mg/g D(+)-sucrose, 5 mg/g proline in Milli-Q

101

deionized water.15 A reconstitution contained all of the volatile compounds detected in

102

jujubes puree in Milli-Q deionized water. The reconstitution was then diluted with

103

water to 1:2, 1:5, 1:10, 1:20, 1:50 and 1:100 strengths. Then, 0.01 g of each of those

104

diluted reconstitution and 0.01 g of the internal standard solution containing 2-octanol

105

(20 mg/kg) were introduced to the 5 g of model solution in a 20 mL vial in order to

106

establish the calibration curves. These mixture solutions were extracted by HS-SPME.

107

Similarly,

108

nitrogenous compounds with internal standard solutions (10 µg/kg of dipropyl

109

disulfide and 20 µg/kg of 2-acetylpyrazine) were prepared to establish the calibration

110

curves for sulfur and nitrogenous compounds, respectively. The standard curve,

111

validation range and coefficient of determination (R2), limits of detection (LOD),

112

limits of quantitation (LOQ) for the volatile compounds were established. The

113

standard curves were shown in the research, where y represented the peak area ratio

114

(peak area of volatile standard/ peak area of internal standard, Ax/Ai) and x

115

represented the concentration ratio (concentration of volatile standard/concentration

0.01

g

of

each

of

those

diluted

6


solutions

of

sulfur

and

Page 7 of 43


116

of internal standard, Cx/Ci). All the experiments were performed in triplicate. The

117

equation for calculate the concentration of volatile compounds is:

118

(Ax/Ai)=a×(Cx/Ci)+b

119

Cx : the concentration of each aroma compound; Ax and Ai were the area of the peak

120

of each volatile compound and the internal standard respectively; a was the slope

121

factor in the standard curves of each compound standard while b was the intercept in

122

them; Ci: the amount of the internal standard. In additional, special response factors

123

were calculated as formula [(Cx/Ax)/(Ci/Ai)].

124

GC-Olfactometry analysis of jujube

125

The GC separation consisted of an Agilent 7890 chromatograph equipped with

126

an ODP-2 Olfactory Detector Port (Gerstel, Mulheim an der Ruhr, Germany). This

127

system allowed us to simultaneously obtain a FID signal and the odor characteristics

128

of each compound detected by sniffing port. GC effluent was split 1:1. The

129

compounds were separated on the DB-Wax analytical fused silica capillary column

130

(60 m×0.25 mm×0.25 µm, Agilent, Santa Clara, CA). The oven temperature was held

131

at 40 °C maintain for 2 min, then ramped at the rate of 2 °C/min to 60 °C, and ramped

132

to 230 °C at the rate of 4 °C/min for 5 min. Moist air was pumped into the sniffing

133

port at 40 mL/min to quickly remove the odorant eluted from sniffing port. The

134

odor-active compounds perceived by ten panelists were recorded as the time for onset

135

and end while sniffing the effluent from the sniffing mask. The panelist also noted the

136

perceived odor characteristic and aroma intensity (AI). The AI was evaluated using

137

10-point intensity scale from 0 to 10; “0” was none, “5” was moderate, and “10” was

138

extreme. The experiment was replicated triplicate by each panelist. Finally, the aroma

139

intensity was the average from ten panelists. The other detailed GC-O analysis was

140

referred to our previous study.8 7



141

GC-MS of volatile compounds in jujube

142

A 6890 gas chromatograph with a 5975 mass selective detector (MSD) (Agilent

143

Technologies, USA) was used. The volatile compounds were separated with DB-Wax

144

and DB-5 analytical fused silica capillary column (60 m×0.25 mm×0.25 µm, Agilent,

145

Santa Clara, CA), respectively. The temperature program was referred to GC-O. The

146

electron impact energy of GC-MS was 70 eV. Its ion source and quadrupole mass

147

filter was set at 230 °C and 150 °C. The injection port was set at 250 °C with splitless

148

mode for 3 mins. The carrier gas was helium at the flow rate of 1 mL/min. The

149

compounds were identified by matching retention times of authentic standards,

150

retention indices (RIs) and mass spectra in the NIST 11 Database. The RIs of

151

unknown compounds were determined by alkanes (C5-C30) (Sigma-Aldrich, St. Louis,

152

MO).

153

HS-SPME-GC-FPD and NPD

154

The Agilent-7890A GC and a flame photometric detector (FPD) was used in the

155

sulfur mode with method of HS-SPME. The columns and oven program were referred

156

to the GC-MS. The temperature of FPD detector was set at 250 °C. PMT voltage was

157

set at 500 V. The injection port was set in a splitless mode for 3 mins at 250 °C. The

158

desorption time was 3 min. The sulfur compounds were identified with retention times

159

of authentic standards and RIs on both columns. Similarly, NPD was used to detect

160

nitrogenous compounds. The temperature of NPD detector was set at 280 °C. The

161

conditions for HS-SPME were referred to the FPD. The same procedure was

162

employed to identify and quantitate the nitrogenous compounds.

163

Odor activity value (OAV)

164

OAV was calculated according to OAV=C/OT, where C was the concentration of

165

compound and OT was its orthonasal detection odor threshold. The threshold values 8


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Page 9 of 43


166

were referred to the literatures in water.

167

Quantitative descriptive sensory analysis

168

The jujube puree was evaluated by a well-trained panel of 15 members (8 males

169

and 7 females). Firstly, 5 g jujube puree was prepared in a 20 mL vial covered with a

170

Teflon over and subjected to panelists without peculiar smell at 25 °C. Then, the

171

panelists had discussed aroma compositions of the jujube puree. Subsequently, the

172

organoleptic characteristic descriptors were quantified using 6 sensory attributes

173

(“roast”, “sweet”, “green”, “sour”, “fruity”, “sulfur”). These descriptors were defined

174

as following aroma: 2-methylpyrazine for “roast” descriptor, (E)-2-hexenal for “green”

175

descriptor, ethyl hexanoate for “fruity” descriptor, β-damascenone for “sweet”

176

descriptor, dimethyl tetrasulfide for “sulfur” descriptor. The score of each sample was

177

presented based on ten point scales (0, none; 5, moderate; 10, very strong). All of the

178

experiment was replicated triplicate by each panelist.

179

Omission experiments

180

Triangle tests were carried out to study the significance of compounds to the

181

overall aroma of jujube. In this experiment, omission models were prepared by

182

omitting one or a group of selected compounds from the complete recombinant aroma

183

model of sample Y1. Each omission model was evaluated against two complete

184

recombination models prepared by mixing the standard aroma compounds at the

185

concentrations in sample Y1. Three different testing samples (5 g each) were

186

randomly assigned to the panelists for sensory evaluation. The test series were

187

replicated triplicate. The significance of difference between omission model and

188

complete recombinate was determined according to the method described.23

189

Impact of compounds added to aromatic reconstitution by threshold

190

In the first phase, three alternative, forced-choice presentation (3-AFC) was 9



191

performed to evaluate the olfactory thresholds of aromatic reconstitution (AR), which

192

was prepared by mixing the standard aroma compounds at the concentrations in

193

sample Y1. Then, AR was evaluated by a well-trained panel of 15 members (8 males

194

and 7 females), respectively. The concentration of AR was placed by the volume. The

195

initial volume of aromatic reconstitution was 0.1 mL. Then the AR was diluted at a

196

factor of 2 with deionized water. Ten volume grades (0.1-51.2 mL) from low to high

197

were used in this experiment. According with the previous literature,24 the

198

concentration (volume)/response function was a psychometric function and the

199

detection threshold was determined by a sigmoid curve (y=1/(1+e(−λx))). Detection

200

probability was corrected using the chance factor (P=(3*p-1)/2, where p = proportion

201

of correct responses for each concentration, and P =proportion corrected by the

202

chance effect, 1/3 for 3-AFC). The detection threshold was defined as corresponding

203

concentration (volume), at which the probability of correct detection was 50%.

204

In the second phase, four compounds (hexanal, 1-octen-3-ol, 3-mercapohexyl

205

acetate and benzaldehyde) with actual concentrations was added to the AR,

206

respectively. The AR defined as specific mixtures. After that, the same procedure was

207

employed to detect the olfactory threshold of specific mixtures. All of the experiment

208

was replicated triplicate by each panelist.

209

Statistical Analysis

210

Statistical analysis of the aroma intensity and concentration of volatile

211

compounds were performed by analysis of variance (ANOVA); differences between

212

samples were evaluated by Duncan’s test that showed significant variation (p < 0.05).

213

All statistical analyses were operated using XLSTAT ver.7.5 (Addinsoft, New York,

214

NY, USA)

215

Results and discussion 10


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216

Optimized HS-SPME conditions

217

In the analytical method developed, several HS-SPME variables including

218

extraction time, extraction temperature, and sample amount should be investigated

219

(Table S1 in the Supporting Information). The extraction time was an important

220

parameter for the extraction efficiency. If the fiber was held in the headspace too long,

221

competition for sites on the fiber would cause inaccuracies in the relative amounts of

222

analytes.

223

min. The results showed that 45 min was required to reach the equilibrium.

25

In our experiment, the jujube puree was extracted for 15, 30, 45, and 60

224

The extraction was strongly influenced by temperature in the HS-SPME

225

analysis.26 However, it was worth pointing out that the volatile compounds in fruit

226

were very likely artifacts formed during the heat impact, esspecially the sulfur

227

compounds.27, 28 Therefore, the low extraction temperatures (25, 30 and 35 °C) were

228

evaluated in experiment. The results showed that the volatile compounds increased

229

with extraction temperature up to 30 °C. Then, volatile compounds reached a stable

230

level with the increase in the temperatures up to 35 °C.

231

The amount of volatile compounds absorbed on the SPME fiber might be

232

dependent on the sample amount.26 The larger the amount of the sample, the more

233

volatile compounds was absorbed by extraction fiber. However, too much sample

234

could cause heat inhomogeneity, and the volatile compounds could not effectively

235

volatilize. Meanwhile, the adsorption of the fiber would become saturated, which was

236

not conducive to better extraction of volatile compounds. In our experiment, the

237

amount of jujube puree was extracted for 3, 4, 5 and 6 g. The results demenstrated that

238

the optimized condition of sample amount was 5 g. On the basis of these observations,

239

the optimized HS-SPME conditions were determined, i.e. 45 min of extraction time,

240

sample amount of 5 g, 30 °C of extraction temperature. 11



241

Page 12 of 43

GC-O and quantitative analysis of volatile compounds in jujube

242

The results of olfactometric analysis were provided in Table 1. Application of

243

GC-O to jujube puree revealed 37, 37, and 35 volatile compounds in the Y1, Y2, and

244

Y3 samples, respectively. The differences in aroma intensities (AIs) of volatile

245

compounds of the samples were mainly caused by concentration differences of these

246

compounds. The AIs of the compounds ranged from 0.3 to 9.4. Beside β-damascenone

247

in Y1, hexanal exhibited highest AIs in Y2 (9.4) and Y3 (9.1), respectively.

248

Amongst those compounds, aldehydes were the greatest class of aroma

249

compounds in jujube puree. A total of nine aldehydes were identified in samples

250

(Table 1), such as heptanal, (E)-2-hexenal, hexanal, (E)-2-heptenal, octanal,

251

(E)-2-octenal, nonanal, furfural, and benzaldehyde. As seen from Table 1, aldehydes

252

were generally considered as “green, cut grass, fat, citrus” notes in sensory

253

descriptions made by panelists. These aldehydes were widespread in many other

254

jujubes.16-18 Within the odor-active aldehydes, hexanal (AI: 8.7-9.4), heptanal (AI:

255

6.7-7.3), and (E)-2-octanal (AI: 6.5-8.5) were the most powerful odor-active

256

compounds contributing to the aroma profile of jujubes. The results were consistent

257

with previous investigations which found that aldehydes with six to ten carbons could

258

be considered as the key contributors to the aroma of fruit.29

259

Besides those aldehyde compounds, ketones and pyrazines were other important

260

classes of odor-active compounds in jujube samples. Specifically, 2,3-butanedione

261

(butter), 2,3-pentandione (butter), 3-hydroxy-2-butanone (butter), acetophenone

262

(musty, almond), β-damascenone (sweet, floral), 2-methypyrazine (roasted),

263

2,5-dimethylpyrazine

264

2,3,5-trimethylpyrazine

265

(roasted, musty) were the most powerful odor-active compounds contributing to the

(nutty,

roasted),

(roasted,


musty),

and

(nutty,

roasted),

2-methoxy-3,5-dimethylpyrazine

12


Page 13 of 43


266

aroma profile of jujube puree.

267

Omission Experiments

268

To take deeper consideration of the aroma contribution of certain compounds, a

269

total of 24 aroma omission models (Table 2) missing either a single compound or a

270

group of compounds were investigated by omission experiments. Each of the

271

omission models was compared with the complete recombinate by a triangle test. The

272

data (Table 2) suggested that all panelists were able to detect the group omission of

273

hexanal,

274

γ-octalactone (model 4) with a very high significance (α ≤ 0.001). Furthermore, model

275

1-1 and model 4-1 without hexanal and β-damascenone were also evaluated with very

276

high significance (α ≤ 0.001) compared to the complete recombinate. Thus, hexanal

277

and β-damascenone might be important contributors for the aroma of jujube puree.

278

The similar result was found in model 2-1, 2-2, 2-3, 3, 3-1, 4-3, 5, 5-2, 8 and 9,

279

indicating that (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, ethyl hexanoate,

280

γ-octalactone, 3-mercapohexyl acetate, benzaldehyde and 1-octen-3-ol might

281

significantly contribute to the overall aroma of jujube puree. These results were

282

consistent with the analysis of GC-O.

heptanal,

octanal

(model

1),

and

β-damascenone,

γ-hexalactone,

283

However, lacking in fatty acids (model 6), the sensory panel was not able to

284

detect a significant difference between omission model and complete recombinate.

285

The same phenomenon also occurred with ethyl octanoate, γ-hexalactone,

286

methanethiol, 3-hydroxy-2-butanone and 2-acetylfuran, as exhibited in model 3-2, 4-2,

287

5-3, 7 and 10, respectively. The results demonstrated that those compounds did not

288

contribute significantly to the overall aroma of jujube puree. These results also agreed

289

with the findings of GC-O analysis.

290

Quantitative analysis and OAV of volatile compounds 13



291

Quantitative analysis and OAV of sulfur compounds

292

As shown in Table 3 and Table S2, 10 sulfur volatile compounds were detected

293

on two dissimilar columns with sulfur-specific FPD. For quantitation purposes,

294

standard curve, validation range and coefficient of determination (R2), LOD and LOQ

295

for each volatile compound were drawn. From Table 3, the observed differences in

296

sulfur compounds presented in the jujube samples were both quantitative and

297

qualitative. Qualitatively, eight, eight, and seven sulfur compounds were identified in

298

samples of Y1, Y2, and Y3, respectively. Quantitatively, difurfuryl sulfide (9.81-12.57

299

µg/kg), methionol (4.72-7.72 µg/kg), methanethiol (5.62-5.68 µg/kg), and dimethyl

300

sulfide (2.05-3.53 µg/kg) were detected at relatively high concentrations in all three

301

samples whilst dimethyl tetrasulfide (0.45-0.48 µg/kg), 3-mercaptohexanol (0.99-1.31

302

µg/kg), and 3-mercaptohexyl acetate (0.067-0.094 µg/kg) were present at trace levels.

303

The contributions of volatile compounds in the samples not only depend on the

304

amounts of each compound but also their odor threshold value. According to results

305

obtained by Guth, those with OAVs greater than 1 were considered to contribute to the

306

aroma of samples.30 From Table 3, 3-mercaptohexyl acetate (OAV: 17-24), methional

307

(OAV: 7-12), 3-mercaptohexanol (OAV: 17-22), and dimethyl sulfide (OAV: 2-3)

308

presented higher OAVs than other sulfur compounds.

309

Difurfuryl sulfide was a sulfur-containing volatile compound that was widely 31, 32

310

distributed in roasted coffee and meat.

From Table 3, this compound was only

311

detected in samples of Y1 and Y2 with highest amounts being 9.813 and 12.575 µg/kg

312

(in terms of sulfur compounds). Although the OAVs of these compounds were not

313

calculated due to the lack of a threshold value, difurfuryl sulfide presented a high

314

aroma intensity in Y1 (3.2) and Y2 (4.3) samples. Thus, difurfuryl sulfide might be an

315

important contributor to the roasted aroma of jujube puree. 14


Page 14 of 43

Page 15 of 43


316

3-Mercaptohexanol (3MH) and 3-mercaptohexyl acetate (3MHA) were

317

responsible for passion fruit, grapefruit, and citrus aromas. Although 3MH and 3MHA

318

had been investigated in previous studies of grape and cranberry fruits 33, 8, they were

319

reported in jujube for the first time here. According to a previous study on grapes,

320

3MH

321

[S-3-(hexan-1-ol)-L-cysteine

322

[S-3-(hexan-1-ol)-glutathione (Glut-3MH).34,

323

esteriﬁcation of 3MH with acetic acid. From Table 3, the amounts of 3MH and 3MHA

324

varied significantly in each of the samples. In the study, the highest concentration of

325

3MH (1.31 µg/kg) and 3MHA (0.09 µg/kg) were detected in the Y3 sample, whilst the

326

lowest concentrations of 3MH (0.99 µg/kg) and 3MHA (0.06 µg/kg) were found in the

327

Y1 sample and Y2 samples, respectively. The amounts of 3MH and 3MHA could be

328

attributed to the variety, climatic conditions, territory, water availability, and

329

environmental conditions. It was also worth noting that 3MH and 3MHA might

330

significantly contribute to the aroma of jujube samples due to their extremely low

331

thresholds of 0.06 µg/kg and 0.004 µg/kg, respectively.36 From Table 3, the OAVs of

332

3MH and 3MHA ranged from 17 to 22, and from 17 to 24, respectively.

was

released

from

precursors,

such

(Cys-3MH) 35

and

as

cysteinylated glutathionylated

3MHA was formed by the

333

Methional, widely found in red wine, mulberry, and cranberry,37, 38 was described

334

as a typical “sulfur, vegetable, cooked potato” note in GC-O analysis. It was regarded

335

as a beneficial compound at low concentrations. Methionol was considered to impart a

336

“vegetable, cabbage” note to the aroma of jujube puree. From the previous research,

337

methionol could be formed by the decarboxylation of 4-methylthio-2-oxobutyric

338

acid.39 From Table 3, the concentrations of methional were 1.62 µg/kg for sample Y1,

339

1.38 µg/kg for sample Y2, and 2.32 µg/kg for sample Y3, respectively.

340

Correspondingly, the OAVs of methional ranged from 8 to 19 in the three samples. 15



Page 16 of 43

341

Thus, methional could potentially play an important role in the aroma of jujube puree.

342

The results were consistent with previous findings indicating that methional was an

343

important contributor to the green vegetable note of fruit aroma.37 In comparison,

344

methionol was only found in Y2 and Y3 samples. Furthermore, the OAVs of

345

methionol were below 1 due to the high threshold (140 µg/kg).

346

Dimethyl sulfide (DMS) was identified in a wide range of rice,40 cheese,41 and

347

grapefruit with an “asparagus, corn, and molasses” aromatic note.6 DMS was derived

348

mainly from S-methylmethionine, which assumed to correspond to stored, and

349

transported, forms of methionine.42-44 Amongst the jujube samples, the concentration

350

of DMS ranged from 2.05 µg/kg to 3.53 µg/kg, indicating that the differences in

351

concentration were small. Correspondingly, the OAVs of this compound ranged from

352

2 to 3. The results demonstrated that DMS contributed to the aroma proﬁles of jujube

353

fruit, which matched the findings of GC-O analysis.

354

Quantitative analysis and OAV of nitrogenous compounds

355

Similarly, a total of nine nitrogenous compounds were identified in three samples

356

by use of NPD. Specifically, six, eight, and seven nitrogenous compounds were

357

detected in Y1, Y2, and Y3 samples, respectively. Quantitatively, 2-methypyrazine

358

(14.80-90.60

359

2,6-dimethylpyrazine (20.59-34.76 µg/kg), and 2,3,5-trimethylpyrazine (15.69-38.97

360

µg/kg) were present at relatively high concentrations in three samples. In comparison

361

to other nitrogenous compounds, 2-acetyl-1-pyrroline (2-AP) (0.61-1.51 µg/kg),

362


363

2-ethyl-3,6-dimethylpyrazine (3.01-5.07 µg/kg) were present in low concentrations in

364

three samples.

365

µg/kg),


(2-MDP)

(57.70-110.46

(0.34-1.05

µg/kg),

µg/kg),

and

Pyrazine compounds were the largest class of nitrogenous compounds found in 16


Page 17 of 43


366

these jujube samples. These compounds were generally associated with “roasted, nutty,

367

earthy” notes in sensory descriptions made by panelists. According to the previous

368

research, pyrazine compounds were sensitive to heat processing.9 As jujubes needed

369

to be dried to remove all of the water during processing, a series of reactions readily

370

occurs, such as the Maillard reaction. As a result, significant amounts of pyrazine

371

compounds were generated. The results were consistent with previous investigation,

372

which showed that pyrazine compounds easily form due to the heating factor.45 In this

373

experiment, 2-methypyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, and

374

2,3,5-trimethylpyrazine were shown to be present in significant amounts in jujubes.

375

Amongst

376

2,6-dimethylpyrazine ranged from 3 to 12. Thus, 2,5-dimethylpyrazine and

377

2,6-dimethylpyrazine were identified as odor-active compounds in jujubes. The

378

results were consistent with the analysis of GC-O.

those

compounds,

the

OAVs

of


and

379

Another pyrazine compound, 2-methoxy-3,5-dimethylpyrazine (2-MDP), was

380

described as imparting an “earthy and roasted” note, which was identified for the first

381

time in raw coffee.10 2-MDP had been detected as a metabolite of aerobic

382

Gram-negative bacteria46, which were isolated from a machine cutting-fluid emulsion.

383

From Table 3, the concentrations of 2-MDP were 1.05 µg/kg for sample Y1,

384

0.87 µg/kg for sample Y2, and 0.34 µg/kg for sample Y3, respectively. Although the

385

amounts of 2-DMP were at trace levels in samples, the OAVs were above 1 due to the

386

low threshold (0.1 µg/kg). Thus, 2-DMP was also considered as an important

387

contributor to the aroma of jujubes.

388

2-AP was described as a characteristic volatile compound with “rice-like,

389

popcorn-like, and roasted” note in rice.40 2-AP was also responsible for the

390

characteristic aroma of white bread47 and bread flowers48. In this experiment, 2-AP 17



391

was identified in jujube puree for the first time. From Table 3, the concentrations of

392

2-AP were 0.61 µg/kg for sample Y1, 1.51 µg/kg for sample Y2, and 0.84 µg/kg for

393

sample Y3, respectively. Although presented at trace levels in all samples,

394

2-acetyl-1-pyrroline demonstrated high OAVs due to the low thresholds (0.1 µg/kg).

395

The result matched the analysis of GC-O.

396

Quantitative analysis and OAV of other compounds

397

The concentrations and peaks of non-sulfur volatile compounds obtained by

398

GC-MS were shown in Table 4 and Figure 1. The concentrations of hexanal

399

(354.68-764.28 µg/kg), phenylmethanol (162.12-578.02 µg/kg), ethyl hexanoate

400

(111.33-192.73 µg/kg), hexanol (53.33-182.52 µg/kg), (E)-2-octenal (95.93-209.55

401

µg/kg), butanol (121.43-205.81 µg/kg), nonanal (186.11-347.81 µg/kg), and acetic

402

acid (39.75-706.90 µg/kg) were higher than those of other compounds. Table 4

403

showed that the type and concentration of aroma volatile differed significantly for

404

various jujube samples. These compounds were possibly formed in the growth

405

process of the jujubes or in their post-processing. Therefore, the existence of the

406

differences in aroma volatile compound concentrations was closely associated with

407

many factors, including the growth environment of the jujubes, soil, climate,

408

post-processing methods, and processing temperature. In addition, hexanal (OAV:

409

39-85), (E)-2-octenal (OAV: 32-70), β-damascenone (OAV: 14-49), ethyl hexanoate

410

(OAV: 22-39), 2,3-butanedione (OAV: 6-13), heptanal (OAV: 8-17), hexanol (OAV:

411

6-20), and phenyl acetaldehyde (OAV: 4-8) presented high OAVs. The results

412

suggested that those compounds contributed greatly to the aroma of jujube puree.

413

Sensory analysis

414

As shown in Figure 2, sensory evaluation was carried out by organoleptic

415

assessments of the quality of three kinds of jujube puree using six descriptors 18


Page 18 of 43

Page 19 of 43


416

including: “roast”, “sweet”, “green”, “sour”, “fruity”, and “sulfur” attributes. The Y1

417

sample was described as “sweet” more often than the other samples. The volatile

418

compounds such as β-damascenone, γ-hexalactone, γ-octalactone and phenyl

419

acetaldehyde might contribute to the “sweet” descriptor. As described by panelists

420

from GC-O, the AIs of β-damascenone ranged from 6.5 to 9.1, indicating that

421

β-damascenone contributed greatly to the “sweet” nature of jujube aroma in these

422

samples.

423

The Y2 sample was accompanied by the “green”, “roast”, and “sour” descriptors.

424

From the analysis of GC-O, compounds such as heptanal, (E)-2-hexenal, hexanal,

425

(E)-2-heptenal, octanal, (E)-2-octenal, and nonanal were the powerful odor-active

426

compounds that contributed to the green aroma profile of jujubes. Similarly, pyrazine

427

compounds were considered as “roasted, nutty, and earthy” notes in sensory

428

descriptions made by panelists. Amongst those compounds, 2,5-dimethylpyrazine and

429

2,6-dimethylpyrazine were identified as odor-active compounds in jujubes. The “sour”

430

descriptor mainly related to sour compounds, such as acetic acid, butanoic acid, and

431

hexanoic acid. Although the amounts of those compounds were high, the OAVs of

432

those compounds were below 1 due to the high threshold. However, those compounds

433

could be perceived by the GC-O.

434

The Y3 sample had the highest rated value of the “fruity” and “sulfur”

435

descriptors, whilst the Y1 sample showed the lowest sensorial scores. The “fruity”

436

descriptor was mainly composed of ester compounds. In this study, ethyl hexanoate,

437

ethyl heptanoate, and ethyl octanoate were identified in the jujube samples. Amongst

438

those compounds, ethyl hexanoate presented high OAVs (22-29) and AIs (6.2-7.5) in

439

the samples. The “sulfur” descriptor was mainly correlated to the presence of sulfur

440

compounds. According to the GC-O and OAV analysis, 3-mercaptohexyl acetate, 19



441

methional, 3-mercaptohexanol, and dimethyl sulfide presented high OAVs and AIs in

442

jujube samples. Thus, those compounds played important roles in imparting the

443

“sulfur” note to the aroma of these jujube samples.

444

Impact of compounds added to aromatic reconstitution

445

From the analysis of GC-O and OAV, hexanal and 3-mercapohexyl acetate

446

contributed greatly to the overall aroma of jujube. The OAVs of 1-octen-3-ol and

447

benzaldehyde were below 1, indicating that those compounds contributed little to the

448

overall aroma of jujube. However, contradiction conclusion of those compounds

449

observed in the omission experiments, suggesting that 1-octen-3-ol and benzaldehyde

450

contributed significantly to the overall aroma of jujube. Thus, those four compounds

451

were further selected in order to verify the contribution to the aroma of jujube.

452

Figure 3 showed that four compounds decreased the threshold value of the

453

overall aromatic reconstitution to differing extents, which reduced the overall

454

threshold value by 2.36, 1.01, 1.34, and 1.19, respectively. It could be seen that

455

hexanal decreased the overall threshold most significantly, indicating that its addition

456

could best increase the overall aroma intensity of aromatic reconstitution. A possible

457

reason for this was the synergies arising between hexanal and the other volatile

458

compounds in the solution. As a result, the aroma intensity of the solution increased

459

and the overall threshold decreased. While 1-octen-3-ol decreased the threshold value

460

of aromatic reconstitution by a small amount, implying that 1-octen-3-ol possibly

461

exerted less influence on other aroma volatiles of aromatic reconstitution. What was

462

worthy of note was that benzaldehyde, at a sub-threshold concentration, reduced the

463

overall threshold value by 1.19. The result demonstrated that benzaldehyde made an

464

important contribution to the overall aroma of the reconstitution as it reduced the

465

threshold value of the solution by interacting with other compounds. The results 20


Page 20 of 43

Page 21 of 43


466

agreed with the findings of previous research, indicating that some volatiles perform

467

an additive, or synergistic function, at sub-threshold concentrations.24,49

468

The effect of compound addition on descriptor intensities

469

Figure 4 showed the influence of four aroma compounds (hexanal, 1-octen-3-ol,

470

3-mercapohexyl acetate, and benzaldehyde) on aromatic reconstitution. The intensity

471

of descriptors varied when the compounds were added to the solution. Except the

472

1-octen-3-ol and 3-mercapohexyl acetate, the addition of hexanal and benzaldehyde

473

highlighted the intensity of “green” descriptor to different extents. Compared with AR,

474

the ratio of intensity ranged from 1.16 to 1.33. The possible reason for this was that

475

the addition of hexanal and benzaldehyde significantly interacted with the compounds

476

with “green” descriptor, such as heptanal, (E)-2-hexenal, hexanal, (E)-2-heptenal.

477

Moreover, the intensity of “sour” decreased to values within the range 0.87 to

478

0.91 after adding benzaldehyde, 3-mercapohexyl acetate and hexanal. The intensity of

479

“sour” was stable after adding 1-octen-3-ol. A possible reason for this was that the

480

addition of benzaldehyde, 3-mercapohexyl acetate and hexanal exhibited a

481

suppressive effect on those volatiles with a sour aroma in the solution, therefore the

482

intensity of sourness therein decreased. It was worth noting that the intensity of

483

“fruity” descriptor increased to 1.28 after adding hexanal. Probably, compound

484

hexanal might interact with ethyl hexanoate and ethyl octanoate, which considered as

485

“fruity” descriptor.

486

To sum up, with all of the findings above taken into account, conclusions could

487

be drawn. 3-Mercaptohexyl acetate, methional, 3-mercaptohexanol, 2-methypyrazine,

488

2,5-dimethylpyrazine, 2,6-dimethylpyrazine, hexanal, (E)-2-octenal, β-damascenone,

489

ethyl hexanoate contributed greatly to the aroma of jujube puree. In addition, four

490

volatiles (hexanal, 1-octen-3-ol, 3-mercapohexyl acetate, and benzaldehyde) were 21



491

selected to investigate their contributions to aromatic reconstitution. The results

492

indicated that those four compounds reduced the overall threshold value to differing

493

extents. Volatile compounds with sub-threshold concentrations might also contribute

494

to the overall aroma. It was of great significance to develop high grade jujube food

495

through determining key odor-active compounds in jujube.

496

ASSOCIATED CONTENT

497

Supporting Information

498

Table S1, A: Extracting time effect on SPME headspace sampling; B: Extracting

499

temperature effect on SPME headspace sampling; C: Sample amount effect on SPME

500

headspace sampling.

501

Table S2, A: The chromatogram of FPD for Y1 sample in DB-Wax column. The

502

number in the peak refered to the identified sulfur compounds in the Table 3.

503

B: The chromatogram of NPD for Y1 sample in DB-Wax column. The number in the

504

peak refered to the identified sulfur compounds in the Table 3.

505

Author information

506

Corresponding Author

507

Correspondence should be addressed to Prof. Xiao Zuobing at the following address,

508

phone number, and email address.

509

Address: No.1800, Lihu Avenue, Wuxi City, Jiangsu Province, People’s Republic of China

510 511

Tel: 0086-0510-85919106

512

Email: [email protected]

513

Funding

514

The research was supported by the National Natural Science Foundation of

515

China (No.2147614090), National Key Research and Development Program 22


Page 22 of 43

Page 23 of 43


516

Nanotechnology Specific Project (No. 2016YFA0200304).

517

Notes

518

The authors declare no competing financial interest.

519

ABBREVIATIONS USED

520

FPD, flame photometric detection; NPD, flame photometric detection;

23



Page 24 of 43

521

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technological parameters on the formation of dimethyl sulfide, 2-mercaptoethanol, methionol, and

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dimethyl sulfone in port wines. J. Agric. Food Chem. 2003, 51, 727-732.

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40. Mahattanatawee, K.; Rouseff, R. L., Comparison of aroma active and sulfur volatiles in three

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fragrant rice cultivars using GC-Olfactometry and GC-PFPD. Food Chem. 2014, 154, 1-6.

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41. Burbank, H. M.; Qian, M. C., Volatile sulfur compounds in Cheddar cheese determined by

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headspace solid-phase microextraction and gas chromatograph-pulsed flame photometric detection. J

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Chromatogr A. 2005, 1066, 149-157.

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42. Segurel, M. A.; Razungles, A. J.; Riou, C.; Salles, M.; Baumes, R. L., Contribution of dimethyl

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sulfide to the aroma of Syrah and Grenache Noir wines and estimation of its potential in grapes of these

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varieties. J. Agric. Food Chem. 2004, 52, 7084-7093.

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43. Howard, A. G.; Freeman, C. E.; Russell, D. W.; Arbab-Zavar, M. H.; Chamberlain, P., Flow

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injection system with flame photometric detection for the measurement of the dimethylsulfide

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precursor β-dimethylsulphoniopropionate. Anal Chim Acta. 1998, 377, 95-101.

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44. Gakière, B.; Denis, L.; Droux, M.; Job, D., Over-expression of cystathionine γ-synthase in

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Arabidopsis thaliana leads to increased levels of methionine and S-methylmethionine. Plant Physiol

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Biochem. 2002, 40, 119-126. 27



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simultaneous distillation and extraction (SDE) with sensory characterisation. Food Chem. 2009, 114,

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microbiologically-produced compound with an obnoxious musty odour. ChemInform,1984,6, 448–449.

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compound, 2-acetyl-1-pyrroline, in bread flowers (Vallaris glabra Ktze). J. Agric. Food Chem. 2003,

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Van Gemert, L. J. Complilations of odor threshold values in air, water and other media. Van

28


Page 28 of 43

Page 29 of 43


656

Figure captions

657

Figure 1. The total ion chromatogram (TIC) of Y1 sample in DB-Wax column. The number (1-46)

658

in the peak refered to the identified aroma compounds in the Table 4.

659

Figure 2. Aroma profiles of jujube puree obtained from Y1, Y2 and Y3 samples.

660

Figure 3. Effect of hexanal, 1-octen-3-ol, 3-mercapohexyl acetate and benzaldehyde addition on

661

the aromatic reconstitution (AR) to detect the variation of threshold.

662

Figure 4. Aromatic impact of hexanal, 1-octen-3-ol, 3-mercapohexyl acetate, and benzaldehyde on

663

aromatic reconstitution.

29



Page 30 of 43

Table 1 GC-O identified odor-active compounds in jujube puree with the method of aroma intensity.

Aroma intensity Code

CompoundsA

RIB

IdentificationC

Aroma description Y1

SD

Y2

SD

Y3

SD

1

methanethiol

696

AD, RI, Std

sulfur, gasoline, garlic

2.7D

0.2

2.9

0.2

-F

-

2

dimethyl sulfide

716

AD, RI, Std

cabbage, sulfur, corn

3.7aE

0.4

4.1a

0.3

4.3a

0.3

3

2,3-butanedione

981

AD, RI, Std

butter

2.3a

0.2

1.8ab

0.2

1.4b

0.1

4

2,3-pentandione

1056

AD, RI, Std

butter

2.1

0.2

-

-

2.2

0.2

5

hexanal

1078

AD, RI, Std

grass, tallow, fat

8.7b

0.7

9.4a

0.9

9.1ab

0.9

6

heptanal

1176

AD, RI, Std

green, leaf

6.7b

0.6

7.3a

1.1

7.1a

1.3

7

(E)-2-hexenal

1194

AD, RI, Std

green, leaf

4.5b

0.6

5.4a

0.6

4.2b

0.6

8

ethyl hexanoate

1220

AD, RI, Std

fruity, wine

6.5b

0.5

6.2b

0.7

7.5a

0.5

9

2-methylpyrazine

1272

AD, RI, Std

roast

2.1

0.2

3.4

0.2

-

-

10

unknown1

1278

AD

green, leaf

-

-

1.4

0.2

1.5

0.1

11

octanal

1284

AD, RI, Std

fat, citrus, green

5.4

0.4

5.1

0.6

-

-

12

3-hydroxy-2-butanone

1288

AD, RI, Std

butter

0.7a

0.1

0.6a

0.1

0.5a

0.1

13


1303

AD, RI, Std

nutty, roasted

4.5b

0.5

5.3a

0.6

4.7b

0.8

14


1328

AD, RI, Std

nutty, roasted

3.7b

0.4

4.1a

0.4

2.4c

0.2

15

(E)-2-heptenal

1332

AD, RI, Std

green, leaf, fat

3.6b

0.8

4.3a

0.6

4.2a

0.3

16

2-acetyl-1-pyrroline

1336

AD, RI, Std

rice, roasted

4.1b

0.3

5.4a

0.3

4.4b

0.3

17

ethyl heptanoate

1336

AD, RI, Std

fruity

-

-

3.2

0.6

4.3

0.3

30


Page 31 of 43


18

hexanol

1360

MS, RI, Std

vegetal, herbaceous

5.6b

0.4

6.5a

0.5

6.8a

0.5

19

nonanal

1387

AD, RI, Std

fat, citrus, green

4.5b

0.9

5.4a

0.7

5.3a

0.9

20

(E)-2-octenal

1409

AD, RI, Std

green, leaf

6.5c

0.4

8.5a

0.8

7.8b

0.6

21

2,3,5-trimethylpyrazine

1419

AD, RI, Std

roast, musty

1.2

0.4

3.4

0.8

-

-

22


1425

AD, RI, Std

roast, musty

3.7a

0.3

3.6a

0.3

2.9b

0.3

23

1-octen-3-ol

1427

AD, RI, Std

mushroom

1.4a

0.2

1.5a

0.1

1.6a

0.2

24

methional

1444

AD, RI, Std

sulfur, cooked potato

4.5a

0.3

3.9b

0.3

4.6a

0.4

25

ethyl octanoate

1445

AD, RI, Std

fruit, fat

2.4b

0.2

3.1ab

0.4

3.5a

0.5

26

acetic acid

1450

AD, RI, Std

sour

0.9a

0.1

1.2a

0.1

0.8ab

0.1

27

furfural

1453

AD, RI, Std

bread, almond, sweet

4.5c

0.4

6.3a

1.2

5.3b

0.6

28

unknown2

1462

AD

floral

1.8a

0.2

1.6a

0.1

1.7a

0.2

29

2-acetylfuran

1493

AD, RI, Std

sweet, almonds, roasted

1.8

0.2

2.6

0.3

-

-

30

benzaldehyde

1498

AD, RI, Std

nutty

0.5b

0.2

1.4a

0.3

0.8ab

0.1

31

unknown3

1576

AD

floral

1.7

0.2

-

-

2.1

0.3

32

phenylacetaldehyde

1625

MS, RI, Std

sweet, fruity

5.1b

0.4

6.3a

0.4

4.7c

0.3

33

acetophenone

1645

AD, RI, Std

musty, almond

-

-

0.8

0.1

0.3

0.0

34

γ-hexalactone

1716

AD, RI, Std

sweet, spicy, coconut, hay

3.4a

0.3

2.6b

1.0

2.7b

0.9

35

3-mercapohexyl acetate

1726

AD, RI, Std

sulfur, grapefruit, fruity

5.8a

0.4

6.1a

0.3

6.3a

0.4

36

unkown4

1806

AD

sweet

2.1

0.3

-

-

1.6

0.1

37

β-damascenone

1815

AD, RI, Std

sweety, floral

9.1a

0.7

8.4b

0.6

6.5c

0.4

31



A

Page 32 of 43

38

hexanoic acid

1836

MS, RI, Std

sour, butter

1.2ab

0.1

1.9a

0.2

0.9b

0.1

39

3-mercaptohexan-1-ol

1876

AD, RI, Std

sulfur, passion fruit

5.2b

0.3

5.3b

0.5

6.4a

0.4

40

γ-octalactone

1881

AD, RI, Std

sweet, coconut, peach

5.4a

0.4

4.3b

0.3

3.2c

0.7

41

difurfuryl sulfide

2227

AD, RI, Std

roasted

3.2

0.3

4.3

0.4

-

-

Volatile compounds perceived in jujube puree; B Retention index of compounds on DB-Wax Column; C RI: retention index; Std: confirmed by authentic standards; AD: Aroma descriptor; D

The aroma intensity was evaluated by GC-O; E: Values with different superscript roman letters (a–c) in the same row are significantly different according to the Duncan test (p< 0.05); F-: not perceive;

32


Page 33 of 43


Table 2 Omission experiments from the complete recombinate

No 1 1-1 1-2 1-3 2 2-1 2-2 2-3 3 3-1 3-2 4 4-1 4-2 4-3 5 5-1 5-2 5-3 6 7 8 9 10 a

b

Odorants omitted from the complete recombinate hexanal, heptanal, octanal hexanal heptanal octanal (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal (E)-2-hexenal (E)-2-heptenal (E)-2-octenal ethyl hexanoate, ethyl octanoate ethyl hexanoate ethyl octanoate β-damascenone, γ-hexalactone, γ-octalactone β-damascenone γ-hexalactone γ-octalactone methional, 3-mercapohexyl acetate, methanethiol methional 3-mercapohexyl acetate methanethiol acetic acid, hexanoic acid 3-hydroxy-2-butanone benzaldehyde 1-octen-3-ol 2-acetylfuran

a

N

Significance

10 9 7 7 9 7 7 8 8 8 5 10 10 5 8 9 7 8 4 3 3 7 7 3

*** *** * * *** * * ** ** **

b

*** *** ** *** * **

* *

Number of correct judgments from 10 panelist evaluating the aroma difference by means of a triangle test. Significance: ***, very highly significant (α ≤ 0.001); **, highly significant (α ≤ 0.01); *, significant (α ≤ 0.05)

33



Page 34 of 43

Table 3 Concentration (µg/kg) and OAVs of sulfur and nitrogenous compounds detected in jujube puree with standard curve, validation range and coefficient of determination (R2), LOD and LOQ. RI Response Compound

Standard curve Wax

DB-5

Validation

LOD

LOQ

detection

range

(µg/k

(µg/k

odor

(µg/kg)

g)

g)

OAV Litera

Identifi No

Orthonasal

Concentration (µg/kg)

factors

2

R

cation

Y1

SD

Y2

SD

Y3

SD

I

tures

Y1

Y2

Y3

threshold (µg/kg)

A

Sulfur 1

methanethiol

696

502

C,D,E

y=1.307x+0.114

0.74

0.983

1-50

0.01

0.03

5.68

0.472

5.62

0.562

-

-

4

46

2

2

Characterization of the Major Odor-Active Compounds in Dry Jujube

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