Photoisomerization of 2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan, a yellow pigment in salted radish roots
Photoisomerization of 2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan, a yellow pigment in salted radish roots
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DOI：
10.1271/bbb.80092
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发表时间：
2008-09-01
影响因子：
1.6
通讯作者：
Uda, Yasushi
中科院分区：
文献类型：
--
作者：
Matsuoka, Hiroki;Honzawa, Shuji;Uda, Yasushi
研究了盐萝卜主要黄色素（E）-2-[3-（2-硫代吡咯烷-3-亚基）甲基]色氨酸（E）-TPMT）的光稳定性。首先，我们分析了（E）-TPMT在长波紫外光照射下产生的光产物。在NMR光谱的基础上，光产物被确定为Z-构型的TPMT，并且通过可见光照射可逆地诱导从Z-异构化为E-形式。E-异构化为Z-的最佳波长为360-380 nm，Z-异构化为E-的最佳波长为440460 nm。在紫外光和可见光照射条件下，光稳态的E/Z比分别约为0.95：1和26：1。在量子产率测量中，（Z）-异构体比（E）-异构体对光照射更敏感。变黄取决于（Z）-异构体的比例，因为B* 和色度值随着色度计测定的（Z）-异构体的增加而升高。因此，在长时间的腌制和发酵过程中，（Z）-异构体的形成可能有助于takuan-zuke的黄色。
The photostability of (E)-2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan ((E)-TPMT), the main yellow pigment in salted radish, was studied. First we analyzed the photoproduct generated from (E)-TPMT under longwave UV irradiation. On the basis of NMR spectroscopy, the photoproduct was identified as Z-configurated TPMT, and isomerization from the Z- to the E-form was reversibly induced by Vis-light irradiation. The optimum wavelength for isomerization from the E- to the Z-form was 360-380 nm, and that for isomerization from the Z- to the E-form was 440460 nm. The E/Z-ratios in the photostationary state under UV- and Vis-light irradiation conditions were approximately 0.95:1 and 26:1 respectively. The (Z)-isomer was more sensitive to light irradiation than the (E)-isomer in the quantum yield measurement. Yellowing was dependent on the ratio of the (Z)-isomer, because the b* and chroma value rose with increases in the (Z)-isomer by the colorimeters. Hence, it is possible that the formation of the (Z)-isomer contribute to the yellow color of takuan-zuke during long salting and fermentation.