94

Proceedings of the 90th JSCM Anniversary Conference
J. Jpn. Soc. Colour Mater., 91〔3〕，94–97（2018）

Photochromic Properties of 3-Deoxyanthocyanidin Pigments Extracted and Purified
from Sorghum Grains
Mai Mihara＊, Kumiko Tasaki＊, Yoshiumi Kohno＊＊ and Masashi Shibata＊,†＊ School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-machi, Hachioji, Tokyo 192-0982, Japan＊＊ Department of Applied Chemistry and Biochemical Engineering, Faculty of Engineering, Shizuoka University,

3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8561, Japan†Corresponding Author, E-mail: mshibata@stf.teu.ac.jp(Received December 1, 2017; Accepted February 8, 2018)
Abstract
With the aim of developing natural photochromic pigments, the selection of source materials and the extraction and purification methods
for 3-deoxyanthocyanidins (3-DAs) were examined. Among the three raw materials derived from sorghum plants, the extract of Japanese
Takakibi with 1, 3-butanediol contained the highest ratio of 3-DAs and exhibited the best photochromic properties. Furthermore, whenfractions containing 3-DAs were collected from these materials using high-performance liquid chromatography (HPLC), the solutions
decolored more readily in the light-shielding state and, hence, their photochromic performance improved drastically. Even Kaoliang foodcolor, which had not previously shown photochromic behavior, showed photochromic performance after HPLC purification.
Key-words: Photochromic pigment, Sorghum, 3-deoxyanthocyanidins, Anthocyanin, HPLC

1．Introduction
Photochromic pigments are the ones that change theircolor when exposed to electromagnetic radiation. To date,many synthetic photochromic pigments have been studied.
Some studies have also been conducted on naturallyoccurring photochromic pigments such as anthocyanidins
and their derivatives, which have a lower environmental
impact and lower human toxicity than synthetic pigments.
Therefore, the industrial production of naturally occurring
pigments is desirable. Luteolinidin, which is one of the
3-deoxyanthocyanidins ( 3-DAs ) present in plants, hasbeen reported to exhibit photochromic behavior in a watermethanol mixture1). 3-DAs are specific anthocyanins thathave no hydroxyl group at the position 3 of the C ring (Fig. 1).
We found that it was possible to repeatedly induce colorationand decoloration with luteolinidin in a nontoxic solution
composed of weakly acidic water and 1,3-butanediol and thatthe other 3-DAs (e.g. apigeninidin, tricetininidin) also exhibit
photochromic behavior2). However, the 3-DAs used in thesestudies were synthetic reagents and it was not clear from
R3'OH
R7O+

R5'

Anthocyanidin

R3’

R5’

R5R7Luteolinidin

OHHOH

OH

Apigeninidin

HHOH

OH

Tricetinidin

OHOHOHOH

R5Fig. 1 Chemical structures of 3-deoxyanthocyanidins ( 3-DAs).

© 2018 Journal of the Japan Society of Colour Materialprior studies whether natural 3-DAs actually extracted fromplants exhibit the same photochromic properties.
Sorghum grains, which are used for food and livestock
feed, are known to contain 3-DAs. Sorghum is primarily
classified on the basis of the color of the seed coat. Amongthese types, black sorghum and brown sorghum are known
to contain a large amount of 3-DAs 3). Besides 3-DAs,sorghums also contain anthocyanin pigments, which are notexpected to show photochromic properties. In this study, weused raw materials derived from sorghums and investigatedwhether the pigments extracted from them actually exhibit
photochromic properties.

2．Experimental
Three types of naturally derived samples (sorghum grains
which are used for food or livestock feed) were used in thisstudy. The first one is a commercial Kaoliang food color,which is extracted and purified from a seed of a type ofsorghums (Sorghum nervosum Bess.). This powder wasexpected to contain a high quantity of anthocyanin pigments.
The second is crushed black sorghum bran (Sorghum bicolor(L.) Moench, T x 430) from the United States, which ismainly used as cow feed and contains a large amount of
3-deoxyanthocyanidins (3-DAs). The third is the shell of
the Japanese Takakibi (Sorghum bicolor Moench) seed fromthe Iwate Prefecture, which is a food grain with a shell thatcan easily and cheaply be obtained as waste material. TheJapanese Takakibi was crushed with a food processor before－14－