218
A.-N. Yu, A.-D. Zhang / Food Chemistry 119 (2010) 214–219
favour the formation of the five reaction products (namely furfural
(3), 2-furanmethanol (4), benzofuran (7), 2,5-furandicarboxalde-
hyde (11), and 2-furfurylfuran (18)). In contrast, high pH values
could promote the production of pyrazines. When the pH of
reaction solution was above 6, the total pyrazines increased obvi-
ously in the model system involving ASA with Thr/Ser. In Fig. 3,
the main pyrazines [2-methylpyrazine (2), 2,5-dimethylpyrazine
(5), 2-ethylpyrazine (6), 2-ethyl-6-methylpyrazine (8), 2-ethyl-5-
methylpyrazine (9), 3-ethyl-2,5-dimethylpyrazine (12), 2,3-
diethyl-5-methylpyrazine (22), and 3,5-diethyl-2-methylpyrazine
(23)] generation in pH 5, 6, 7, 8, and 9.55 aqueous solutions, by
heating a model system containing ASA with Thr/Ser, are com-
pared. Higher amounts of pyrazines were identified from the reac-
tion of ASA with Thr/Ser from pH 8.00 to 9.55. The thermal
degradation of ASA can produce many carbonyl compounds (Ver-
nin, Chakib, Rogacheva, Obretenov, & Párkányi, 1998). The base
catalysis was probably due, both, to the increased reactivity of
the amino group of the amino acid toward the carbonyl and to
the increased rearrangement and fragmentation of ASA (Koehler
& Odell, 1970). Pyrazines may contribute to the toasted, roasted,
nutty, and burnt notes.
Benzofuran (Shephard, Nichols, & Braithwaite, 1999), furfural
(3) and 3-ethyl-2-hydroxy-2-cyclopenten-1-one (Vernin et al.,
1998) were products from the thermal degradation of ascorbic
acid. 2-Furanmethanol (4) was formed by reduction of furfural.
2-Furfurylfuran was possibly formed by reduction of 2-furoylfuran,
which was a product from thermal degradation of ascorbic acid
(Vernin et al., 1998).
Pyrazine is one of the most important groups amongst the iden-
tified volatiles in the studied systems. They are widely distributed
in food systems, especially foods processed at high temperatures
and low humidity. A review on pyrazines in food has been pub-
lished (Maga, 1992). There are several precursors or pathways for
findings support an earlier observation that pH has a great influence
on volatile compounds formed in Maillard-type reactions.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (20876036) and the Project of Team Research for Excellent
Mid-Aged and Young Teachers of Higher Education of Hubei Prov-
ince, China (T200707) for the financial support of this
investigation.
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Yu, Ai-Nong
