664
J. Agric. Food Chem. 1998, 46, 664−667
Mech a n istic Stu d ies on th e F or m a tion of Th ia zolid in e a n d
Str u ctu r a lly Rela ted Th ia zin es in a Cystea m in e/2,3-Bu ta n ed ion e
Mod el System
Tzou-Chi Huang,*,† Yu-Ming Su,† and Chi-Tang Ho‡
Department of Food Science and Technology, National Pingtung University of Science and Technology,
912 Pingtung, Taiwan, and Department of Food Science, Rutgers University,
New Brunswick, New J ersey 08901
Phosphate was found to dramatically enhance the formation of 2-methyl-2-acetylthiazolidine from
a cysteamine/2,3-butanedione model system. In addition to the major component, 2-methyl-2-
acetylthiazolidine, significant amounts of two structurally closely related compounds, 2-acetyl-2,3,5,6-
tetrahydro-1,4-thiazine and 5-acetyl-2,3-dihydro-1,4-thiazine, were characterized by using GC/MS
(CI and EI). There was an oxidative transformation of 2-acetyl-2,3,5,6-tetrahydro-1,4-thiazine to
5-acetyl-2,3-dihydro-1,4-thiazine in the presence of azodicarbonamide. A formation mechanism for
2-methyl-2-acetylthiazolidine and structurally related 2-acetyl-2,3,5,6-tetrahydro-1,4-thiazine and
5-acetyl-2,3-dihydro-1,4-thiazine is proposed.
Keyw or d s: 2-Acetyl-2,3,5,6-tetrahydro-1,4-thiazine; cysteamine; 2,3-butanedione; popcorn-like
compounds; oxidative transformation
INTRODUCTION
Interestingly, thiazolidine and thiazine formation
were reported by different research groups, respectively,
from the same model system, cysteamine and 2,3-
butanedione. The objective of this research is to inves-
tigate in detail the formation of 5-acetyl-2,3-dihydro-
1,4-thiazine and 2-acetyl-2-methylthiazolidine from the
same model system.
Model systems composed of D-glucose and L-cysteine
have long been used to study the thermal generation of
nitrogen- and sulfur-containing flavor compounds (Scan-
lan et al., 1973; Mulders, 1973). Among the volatile
compounds identified, thiazolidines and thiazines are
of special interest.
Thiazolidines generally possess a characteristic pop-
corn-like flavor (Yeo and Shibamoto, 1991). 2-Acetyl-
2-methylthiazolidine was first characterized by Umano
et al. (1995) from the headspace of a heated D-glucose/
L-cysteine model system. The yield of 2-acetyl-2-meth-
ylthiazolidine is <0.01% (GC peak area). Umano et al.
(1995) hypothesized that the reaction between cysteam-
ine, the decarboxylated cysteine, and 2,3-butanedione,
a glucose degradation product, may lead to the forma-
tion of 2-acetyl-2-methylthiazolidine. However, no de-
tailed formation mechanism was provided.
On the other hand, an intensely roasted, popcorn-like
odorant, 5-acetyl-2,3-dihydro-1,4-thiazine, was identi-
fied in a D-ribose/L-cysteine model system by Hofmann
et al. (1995a). It was proposed that a Schiff base was
formed from the condensation between the amino group
in cysteamine and the carbonyl group in 2,3-butane-
dione. Tautomerization and subsequent cyclization by
a Michael-type nucleophilic attack of the thiol group at
the activated methyl carbon atom yielded 5-(2-hydroxy-
ethenyl)-2,3,6-trihydro-1,4-thiazine. Oxidation of this
enaminol results in 5-acetyl-2,3-dihydro-1,4-thiazine,
which, due to the electronegativity of the sulfur atom,
tautomerizes into the more stable 5-acetyl-2,3-dihydro-
1,4-thiazine (Hofmann et al., 1995a).
EXPERIMENTAL PROCEDURES
Ma ter ia ls. Cysteamine, tributylamine, and 2,3-butanedi-
one were purchased from Aldrich Chemical Co. (Milwaukee,
WI). Sodium hydroxide, disodium hydrogen phosphate, so-
dium dihydrogenphosphate dihydrate, and azodicarbonamide
were of chemical grade and obtained from Sigma Chemical
Co. (St. Louis, MO).
Sa m p le P r ep a r a tion . Cysteamine (1 mM) and 2,3-butane-
dione (1 mM) were dissolved in either deionized water (100
mL) or a phosphate buffer (100 mL, pH 7.2, 0.2 M). Samples
were put into a glass tube, capped tightly, and heated for 20
min in a laboratory autoclave at 121 °C. After cooling, the
solution was extracted with dichloromethane. An internal
standard, tributylamine (1 mM), was added to the extract.
Effect of P h osp h a te Bu ffer on 2-Acetyl-2-m eth ylth i-
azolidin e, 5-Acetyl-2,3-dih ydr o-1,4-th iazin e, an d 2-Acetyl-
2,3,5,6-tetr a h yd r o-1,4-th ia zin e F or m a tion . Reaction mix-
tures without phosphate were adjusted to pH 7.2 with sodium
hydroxide. To study the effect of the buffer system on the
generation of volatile compounds in the model system, a
phosphate buffer (0.2 M, pH 7.2) was utilized to replace the
aqueous medium.
Effect of Azod ica r bon a m id e on 5-Acetyl-2,3-d ih yd r o-
1,4-th ia zin e F or m a tion . To investigate the redox reaction
in the model system, various concentrations of azodicarbon-
amide (0, 1, 2, and 3 mM) were added to the heated and then
cooled solution and shaken in a water bath (35 °C) for 30 min.
After shaking, the solution was extracted with dichlo-
romethane. An internal standard, tributylamine (1 mM), was
added to the extract.
* Author to whom correspondence should be addresssed (fax
886-87740213; e-mail tchuang@mail.npust.edu.tw).
† National Pingtung University of Science and Technology.
‡ Rutgers University.
Ga s Ch r om a togr a p h y (GC). An HP 5890 A gas chro-
matograph (Hewlett-Packard, Palo Alto, CA) equipped with a
S0021-8561(97)00602-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/06/1998