ISHS Acta Horticulturae 1361: XXXI International Horticultural Congress (IHC2022): International Symposium on Natural Colorants from Plants
HPLC analyses of indigo, indirubin, and isatin spontaneously formed in plant leaves |
| Author: | Z.C. Koren |
| Keywords: | indigo, indirubin, isatin, precursors, indican, isatans, indoxyls |
| DOI: | 10.17660/ActaHortic.2023.1361.7 |
| Abstract:
There are more than a dozen precursors in the leaves of all indigo-producing plants and they are mainly indoxyl and dioxindole derivatives with different attached sugar moieties. The gamut of these possible compounds include indican, and isatans A, B, and C. Hydrolysis of these precursors will cleave the glycosyl groups and leave the indoxyl and dioxindole aglycones to further react with oxygen and consequently form colored compounds. The main colorant product is typically, of course, the bluish indigo pigment (also known as “indigotin”), with usually some reddish indirubin and yellowish isatin also produced. Indirubin is an isomer of indigo, and the less-colored isatin is an oxidized form of a “half-indigo” molecule. A few interesting properties were observed in analyzing such plant leaves. Even fresh leaves, immediately after their cutting from the plant, will already show the presence of indigo in them. In some plants, it is possible to produce an unusually large amount of indirubin, and, when combined with the indigo that is also produced, reddish purple colors are observed. Alternatively, some leaves can also form a significant amount of yellowish isatin together with indigo and thus resulting in a combined greenish color. This study will quantify the amounts of dyes spontaneously produced in the leaves of various indigo-producing plant species. The plant materials studied include relatively fresh, dried, crushed, couched leaves, as well as aged leaves and those stored in plastic and in paper. | |
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