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Formation of red pigment by a two‐step 2‐thiobarbituric acid reaction of alka‐2,4‐dienals. Potential products of lipid oxidation
Author(s) -
Kosugi Hiroko,
Kato Tetsuta,
Kikugawa Kiyomi
Publication year - 1988
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02535647
Subject(s) - pigment , chemistry , adduct , aldehyde , acetic acid , organic chemistry , oxygen , yield (engineering) , thiobarbituric acid , aqueous solution , antioxidant , catalysis , lipid peroxidation , materials science , metallurgy
Reaction of 2,4‐hexadienal, 2,4‐nonadienal and 2,4‐decadienal with 2‐thiobarbituric acid (TBA) in aqueous acetic acid produced a 532‐nm absorbing red pigment. While the 1∶1 reaction of the aldehyde and TBA produced little pigment, reaction of the aldehyde with an excess amount of TBA produced significant amounts. Instant heating of the reaction mixture did not produce the pigment. However, initial reaction at 5°C and subsequent heating to 100°C produced the pigment efficiently (two‐step reaction). Pigment formation required water and dissolved oxygen. The yield of the pigment from the alka‐2,4‐dienals was 1/10–1/20 of that from malonaldehyde. In the first step of the reaction at 5°C, the 1∶1 adducts of the aldehydes at the 5 ‐position of TBA and several other uniden‐tified adducts were formed. In the second step, these adducts were converted at 100°C, in the presence of water and oxygen, into the red pigment. The structure of the red pigment from 2,4‐hexadienal was elucidated to be the 1∶2 adduct of malonaldehyde and TBA. 2‐Hexenal and t ‐butylhydroperoxide showed marked synergistic effects on the pigment formation from the alka‐2,4‐dienals. Red pigment formation due to the alka‐2,4‐dienals may be enhanced by the presence of other aldehydes and hydro‐peroxides.