Distribution and Importance
Cinnamon, the dried bark and twig of Cinnamomum spp. (Lauraceae), is one of the most popular and the oldest spices used for foods, confectionery, and mulled wine. It is also an important crude drug very frequently prescribed in Chinese and Japanese traditional medicine, and it has been used as stomachic, carminative, diaphoretic, astringent, analgesic, and antipyretic in Asian countries. Cinnamon is also a component of herb tea in Europe.
The cinnamon in Asian traditional medicines is represented by C. cassia Blume, which is called cassia or Chinese cinnamon, although some other Cinnamomum spp., such as C. zeylanicum Nees, C. burmanni Blume, and C. obtussifolium Nees, etc. are also used under the name of cinnamon.
The trees of C. cassia () grow and are cultivated only in tropical and subtropical countries, especially in the southern part of China and the eastern part of India. Wild trees reach naturally over 10 m in height, but they can be cultivated as bushes of a height between 2 and 3 m with regulated branches.
Although cinnamaldehyde, a phenylpropanoid, is well known as the component characteristic of the aroma of cinnamon, condensed tannins in this plant have been proposed to be the main component responsible for its medicinal effects.
Tannins, a large group of polyphenolic compounds, are generally classified into two groups; hydrolyzable tannins which are esters composed of polyphenolic acids (e.g., gallic acid and hexahydroxydiphenic acid) and glucose (or some other sugar or polyalcohol), and condensed tannins, which are condensates of flavan unit, such as ( + )-catechin and ( – )-epicatechin.
Cinnamomum spp. contain a large amount of condensed tannins which are also called proanthocyanidin, since they release anthocyanidin when heated in the presence of acid. In the structures of condensed tannins, the condensation occurs mostly between C4 of a flavan unit and C8 and/or C6 of another unit. A large structural variety of condensed tannins is induced by the combination of different condensation pattern, degree of condensation, and variation in the monomer structure. They are widely distributed in foods, e.g., grape, persimmon, tea; and in various medicinal plants, e.g., Uncaria gambir Roxb., Rheum spp., Ephedra spp., and also in industrial tannin sources such as mangrove (several plants of the Rhizophoraceae), wattle bark (Acacia spp.), and quebracho (Quebrachia lorentzii, Schinopsis balansae). The condensed tannins in the bark of cinnamon are predominantly condensates of ( + )-catechin and ( — )-epicatechin.
Conventional Practice for the Propagation of Cinnamon
The propagation of cinnamon tree has usually been done by seeding or layering. Efficient cultivation of the cinnamon tree requires loamy and humus soil, with a temperature over 10 °C in winter.
In the conventional way, however, it takes a long time to grow the tree for the purpose of obtaining its bark for medicinal use. There is also difficulty in controlling its growth and the production of condensed tannin in intact trees.
Summary and Conclusion
The tannin content in the suspension cells cultured in liquid medium, calculated per dry weight, was 11.7 mg/g cells, while the tannin content in the intact leaves was 29 mg/g dry wt. Although the total tannin content of the suspension cultures was lower than that of the intact leaves at present, the cell cultures are capable of producing a larger amount of tannins, since no special selection concerning tannin production was applied to these cell cultures in the present work.
Cell cultures provide a system for biochemical studies of procyanidins preferable to the intact tree, because the cell growth and the tannin production in this system is controlled more easily than in the intact tree. This system is particularly suitable for biosynthetic studies of condensed tannins, since the composition of phenolic constituents in the cell cultures are much simpler than in the intact plant. It appears that these Cinnamomum cell cultures produce no other phenolic compounds than condensed tannins in chromatographically discernible amounts. This is an advantage for the tracer experiments of condensed tannin biosynthesis. It seems that cinnamaldehyde (at least in free form) was not synthesized by the present cell cultures.
The best explant for the establishment of condensed tannin-producing cell cultures from C. cassia is fresh petiole or midrib of the young leaves, in our experience. Callus tissues are induced on LS agar medium supplemented with 10-5 M IAA and 10-5 M BA at 25 °C in the dark. Calli can be subcultured on LS medium containing 0.2% gellan gum and the same growth regulators as above, although coconut milk 5% or malt extract 0.4% should be added to the medium for better tannin production. The suspension cultures are initiated from calli by agitating in LS liquid medium containing 5% coconut milk, and the same concentration of IAA and BA as above. Fine cell suspension cultures could be obtained by selecting fine cell suspension with pipet on subculture. The suspension cultures are producing condensed tannin, and the highest tannin content is observed ca. 35 days after inoculation.