Photoisomerization of 2-[3-(2-Thioxopyrrolidin-3-ylidene) methyl]-tryptophan, a Yellow Pigment in Salted Radish Roots

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Abstract

The photostability of (<I>E</I>)-2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan ((<I>E</I>)-TPMT), the main yellow pigment in salted radish, was studied. First we analyzed the photoproduct generated from (<I>E</I>)-TPMT under longwave UV irradiation. On the basis of NMR spectroscopy, the photoproduct was identified as <I>Z</I>-configurated TPMT, and isomerization from the <I>Z</I>- to the <I>E</I>-form was reversibly induced by Vis-light irradiation. The optimum wavelength for isomerization from the <I>E</I>- to the <I>Z</I>-form was 360–380 nm, and that for isomerization from the <I>Z</I>- to the <I>E</I>-form was 440–460 nm. The <I>E</I>/<I>Z</I>-ratios in the photostationary state under UV- and Vis-light irradiation conditions were approximately 0.95:1 and 26:1 respectively. The (<I>Z</I>)-isomer was more sensitive to light irradiation than the (<I>E</I>)-isomer in the quantum yield measurement. Yellowing was dependent on the ratio of the (<I>Z</I>)-isomer, because the <I>b</I><SUP>*</SUP> and chroma value rose with increases in the (<I>Z</I>)-isomer by the colorimeters. Hence, it is possible that the formation of the (<I>Z</I>)-isomer contribute to the yellow color of <I>takuan-zuke</I> during long salting and fermentation.

Journal

  • Bioscience, Biotechnology, and Biochemistry

    Bioscience, Biotechnology, and Biochemistry 72(9), 2262-2268, 2008-09-23

    Japan Society for Bioscience, Biotechnology, and Agrochemistry

References:  26

Cited by:  2

Codes

  • NII Article ID (NAID)
    10027531602
  • NII NACSIS-CAT ID (NCID)
    AA10824164
  • Text Lang
    ENG
  • Article Type
    Journal Article
  • ISSN
    09168451
  • NDL Article ID
    9748275
  • NDL Source Classification
    ZR7(科学技術--農林水産--農産) // ZR2(科学技術--生物学--生化学) // ZP1(科学技術--化学・化学工業)
  • NDL Call No.
    Z53-G223
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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