224
J. Agric. Food Chem. 1998, 46, 224−227
Mech a n istic Stu d ies on Th ia zolid in e F or m a tion in Ald eh yd e/
Cystea m in e Mod el System s
Tzou-Chi Huang,*,† Lee-Zen Huang,† 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 08903
A mechanism was proposed to elucidate the formation of a thiazolidine in aldehyde/cysteamine
model systems. Buffer dramatically promotes thiazolidine formation from formaldehyde and
cysteamine. Phosphate tends to stabilize the primary carbocation formed, and this may lead to
completion of the cyclization by attack of the amino nitrogen on the activated carbon. Protic solvent,
by removing the water molecule, further enhances thiazolidine formation. Redox reaction catalyzed
by phosphate ions results in the conversion of thiazolidine to the corresponding thiazoline through
hydride transfer.
Keyw or d s: Cysteamine; aliphatic aldehyde; formaldehyde; thiazoline; thiazolidine; redox reaction
INTRODUCTION
dehyde (bp -19 °C) and acetaldehyde (bp 20.8 °C). It
is well documented that a Schiff base formed between
The volatile carbonyl compounds, especially alde-
the amino group of cysteamine and the aldehyde group
hydes, are important contributors to rancid and un-
of formaldehyde (Hayashi et al., 1986). In our previous
pleasant flavors in various lipid-containing foods. They
studies, a significant combined effect of buffer and protic
are formed from oxidation or decomposition of lipid
solvent on Schiff base formation was observed (Huang,
during the storage of food. Because of their detrimental
1997). The objective of this experiment is, therefore,
effects to the nutritional value of food or their potential
to investigate mechanistically the formation of thiazo-
carcinogenic property, it is necessary to measure the
lidine between cysteamine and aldehydes.
levels of volatile aldehyde compounds in food.
EXPERIMENTAL PROCEDURES
Quantitative analysis of highly volatile and reactive
aldehydes such as formaldehyde and acetaldehyde has
been the subject of several studies (Gray, 1978; Frankel,
1987). Most commonly used analysis methods for these
aldehydes involved derivatization with 2,4-dinitrophen-
ylhydrazine (Stanley et al., 1975; Caporaso and Sink,
1978). However, this derivatization requires a strong
acidic condition which may cause undesirable reactions
such as decomposition of trimethyl oxide, carbohydrate,
lipid, and protein.
Ma ter ia ls. Formaldehyde, acetaldehyde, propionaldehyde,
butyraldehyde, and valeraldehyde were purchased from Ald-
rich Chemical Co. (Milwaukee, WI). Disodium hydrogen
phosphate, sodium dihydrogen phosphate dihydrate, sodium
carbonate, sodium hydrogen carbonate, trisodium citrate di-
hydrate, citric acid monohydrate, sodium acetate, and sodium
hydroxide were of chemical grade and obtained from Nacalai
Tesque, Inc. (Kyoto, J apan). Ethanol, chloroform, and cys-
teamine were purchased from Sigma Chemical Co. (St. Louis,
MO).
Recently, a thiazolidine derivative method for the
determination of trace aldehydes in foods and beverages
has been developed (Hayashi et al., 1986; Miyashita et
al., 1991). This method is based on the reaction of vola-
tile carbonyl compounds with cysteamine (2-aminoeth-
anethiol) to form stable thiazolidine derivatives under
mild conditions (room temperature and neutral pH). The
thiazolidine derivatives formed were subsequently de-
termined by gas chromatography. However, the forma-
tion pathways of thiazolidines are not yet well docu-
mented.
Yasuhara and Shibamoto (1991) reported that it was
difficult to obtain consistent results from replicate
experiments on formaldehyde and acetaldehyde analy-
sis. Only limited amounts of formaldehyde and acetal-
dehyde were able to be trapped by cysteamine. They
attributed this mainly to the high volatility of formal-
Rea ction P r oced u r e. Reaction mixtures were composed
of 0.6 g of cysteamine and ∼0.02 g of aldehydes (formaldehyde,
0.667 mmol; acetaldehyde, 0.455 mmol; propionaldehyde, 0.345
mmol; butyraldehyde, 0.278 mmol; and valeraldehyde, 0.233
mmol), dissolved in 50 mL of deionized water or buffer
solutions. Buffers involving carbonate, phosphate, citrate, and
acetate were used, and the final pH value of the reaction
mixture was adjusted to the pH equivalent to the pKa value
of each salt with sodium hydroxide; the mixtures were then
made up to a final volume of 100 mL. To study the effect of
buffer capacity on thiazolidine formation, different proportions
of anion phosphate (0.025, 0.05, 0.1, and 0.2 M) and an initial
pH of 7.2 were used to replace the aqueous medium described
previously. Potassium chloride was utilized to maintain a
constant ion strength for all three model systems following
the method of Reynolds (1959). All of the reactions were run
at 25 °C for 30 min, and then 1 mL of tributylamine (0.2 mg/
10 mL chloroform) was added as an internal standard for GC
analysis. The reaction mixtures were extracted two times with
10 mL of chloroform each time, and the extract was made up
to 25 mL with chloroform. After drying over Na2SO4, 10 µL
of the chloroform extract was subjected to GC analysis.
Effect of Eth a n ol Con ten t on Th ia zolid in e F or m a tion .
Different percentages of ethanol (0, 20, 40, 60, and 80%) in
* Author to whom correspondence should be addressed (fax
886-87740213; e-mail tchuang@mail.npust.edu.tw).
† National Pingtung University of Science and Technology.
‡ Rutgers University.
S0021-8561(97)00563-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/19/1998