Chapter 14
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Analysis of Thermal Degradation Products of Allyl Isothiocyanate and Phenethyl Isothiocyanate Chung-Wen Chen, Robert T. Rosen, and Chi-Tang Ho Department of Food Science and Center for Advanced Food Technology, Cook College, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, N J 08901-8520 Allyl isothiocyanate (AITC) or phenethyl isothiocyanate (PEITC) in an aqueous solution were heated and refluxed at 100 C for 1 hr. The reaction mixtures were simultaneously distilled and extracted into methylene chloride using a Likens-Nickerson (L-N) apparatus and then analyzed using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The mixtures in the aqueous phase were analyzed by high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) equipped with an atmospheric pressure chemical ionization (APCI) interface. Nine thermal degradation volatile products including diallyl sulfide, diallyl disulfide, diallyl trisulfide, diallyl tetrasulfide, allyl thiocyanate, 3H-1,2-dithiolene, 2vinyl-4H-1,3-dithiin, 4H-1,2,3-trithiin, and 5-methyl-1,2,3,4tetrathiane were identified from AITC; while no volatile degradation products from PEITC were found. N,N'-diallylthiourea and N , N ' diphenethylthiourea, which were the major degradation products in the aqueous phase from the thermal reaction of AITC and PEITC, respectively, were identified by LC-MS (APCI+), direct probe EI-MS and H -NMR. A possible mechanism for the formation of these products is proposed.
In mustard and other cruciferous vegetables such as cabbage and cauliflower, allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC) are generated from their precursors, the glucosinolates, namely sinigrin and gluconasturtiin, respectively (7,2). These glucosinolates break down and release isothiocyanates such as AITC and PEITC by the action of myrosinase (thioglucoside glucohydrolase) when the plant tissue is disrupted (7,3-5). This action is presented in Figure 1.
152
©1998 American Chemical Society In Flavor Analysis; Mussinan, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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1 diallyl sulfide
2 allyl isothiocyanate
3 allyl thiocyanate
4 diallyl disulfide
5 3H-l,2-dithiolene
6 diallyl disulfide
7 2-vinyl-4H-l ,3-dithiin
8 4H-l,2,3-trithiin
9 5-methyl-l,2,3,4-tetrathiane
^ X ^ s
10 diallyl tetrasulfide Figure 3. Thermal decomposition products identified from allyl isothiocyanate.
ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
Downloaded by UNIV MASSACHUSETTS AMHERST on September 29, 2012 | http://pubs.acs.org Publication Date: September 10, 1998 | doi: 10.1021/bk-1998-0705.ch014
160
•ZD
1
5
10
Min.
Figure 6. HPLC chromatogram of the nonvolatile products generated from thermal reaction of phenethyl isothiocyanate.
In Flavor Analysis; Mussinan, C., et al.;
188 (0) 202 (0) 216 (0)
103(100), 143(74.8), 75(63.5), 47(58.3), 55(51.7), 97(50.6), 43(30.6), 57(28.8)
103(100), 47(41.7), 157(35.5), 69(31.9), 57(31.8), 75(29.6), 55(18.9), 41 (16.5)
103(100), 75(31.0), 47(26.5), 171(26.0), 69(24.9), 57(15.3), 55(12.9), 41(12.5)
103(100), 43(57.1), 57(54.6), 41(57.1) 55(41.5), 75(28.5), 47(26.6), 69(23.1)
161(100), 133(72.7), 105(48.3), 55(46.8), 131(42.7), 103(39.7), 77(39.3), 115(31.6)
103(100), 47(62.2), 75(46.6), 91(28.2), 121 (21.5), 149(17.6), 104(6.7), 65(6.3)
heptanal diethyl acetal
octanal diethyl acetal
nonanal diethyl acetal
dodecanal diethyl acetal
cinnamaldehdye diethyl acetal
phenyl acetaldehyde diethyl acetal
3
2
'M = Molecular ion (% abundance) M-1 = Molecular ion minus H (% abundance) RI = GC retention index on non-polar, polydimethylsiloxane capillary column relative to n-paraffin series
226 (0.5)
69(100), 87(99.2), 41(52.7), 181(34.6), 103(27.9), 83(21.5), 59(20.7), 75(19.6)
citral (neral/geranial) diethyl acetal
194 (0)
206 (17.3)
258 (0)
(0)
160
103(100), 75(79.0), 115(66.3), 47(62.5), 69(56.4), 71(48.5), 43(38.3), 45(25.5)
isovaleraldehyde diethyl acetal
M
172 (2.9)
!
57(100), 127(100), 85(67.2), 41(42.5), 43(32.3), 99(31.3), 129(28.4), 69(26.2)
Characteristic Mass Spectral Ions and Abundances
trans-2-hexenal diethyl acetal
Acetal
Table I. Mass Spectra of Diethyl Acetals
171 (1.7)
M-1
193 (0.1)
205 (3.3)
257 (0)
215 (0.3)
201 (0.5)
187 (0.8)
225 (0.6)
159 (0.5)
2
RI
1307
1518
n.d.
1319
1307
1186
1514
986
1031
3
