Structure of two purple pigments, catechinopyranocyanidins A and B from the seed-coat of the small red bean, Vigna angularis

The small red bean, Vigna angularis , is primarily used to produce the “an-paste” component of Japanese sweets. Through the manufacturing process, the red seed-coat pigment is transferred to the colorless “an-particles”, imparting a purple color. However, the major pigment in the seed coat has not y...

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Bibliographic Details
Published in:Scientific reports 2019-02, Vol.9 (1), Article 1484
Main Authors: Yoshida, Kumi, Nagai, Nobukazu, Ichikawa, Yoshiki, Goto, Miki, Kazuma, Kohei, Oyama, Kin-ichi, Koga, Kazushi, Hashimoto, Masaru, Iuchi, Satoru, Takaya, Yoshiaki, Kondo, Tadao
Format: Article
Language:English
Subjects:
119/118
140/131
631/92/349
639/638/403/936
Catechin
Chemical properties
Color
Humanities and Social Sciences
Hydrophobicity
Manufacturing industry
multidisciplinary
Pigments
Science
Science (multidisciplinary)
Seed coats
Sugar
Vigna angularis
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Summary:The small red bean, Vigna angularis , is primarily used to produce the “an-paste” component of Japanese sweets. Through the manufacturing process, the red seed-coat pigment is transferred to the colorless “an-particles”, imparting a purple color. However, the major pigment in the seed coat has not yet been identified, although it is historically presumed to be an anthocyanin. Here, we report the isolation and structural determination of two hydrophobic purple pigments in the seed coat via instrumental analysis and derivatization. The new pigments, catechinopyranocyanidins A and B, contain a novel pyranoanthocyanidin skeleton condensed with a catechin and cyanidin ring system, and no sugar moieties. Catechinopyranocyanidins A and B are diastereomers with a different configuration at the catechin moiety, and both are purple in color in strongly acidic-to-neutral media. Catechinopyranocyanidins A and B are very stable under dark conditions, but, labile to light and decompose to colorless compounds. Thus, these pigments exhibit quite different chemical properties compared to simple anthocyanidins.
ISSN:2045-2322
2045-2322
DOI:10.1038/s41598-018-37641-0