1991 Volume 60 Issue 2 Pages 429-435
With the purpose of developing a new industrial utilization of kaki-shibu, antimutagenic activity of kaki-tannin purified from kaki-shibu on UV-induced mutagenesis was examined and reported in this paper. The activity was evaluated by counting the number of revertant colonies (Trp+) from a strain of Escherichia coli B/r WP2 (Trp-) in media + kaki-shibu fractions after ultraviolet (UV) irradiation.
1. Although kaki-shibu powder itself did not give any large effect on UV-induced mutagenesis, a kaki-shibu residue from which tannin had been removed and a purified kaki-tannin from kaki-shibu at a mg per agar plate, respectively, yielded a 58% and 72% relative mutagenic activity (RMA). A mixture of chemically degraded products from kaki-tannin at a mg per plate resulted in a 37% RMA, a significant antimutagenic potential.
2. Purified kaki-tannin (10 g), degraded in an acidic ethanol-phloroglucinol solution by heating at 80°C for 3 days, resulted in four monomeric phloroglucinol-derivatives. Their arbitrary labels based on their order of Rf values on silica gel-TLC and yields are:. A (72 mg) ; B (197 mg) ; C (47 mg) ; D (63 mg). Their antimutagenic activities in decreasing order are: B, D, C and A. That is, components B and A, phloroglucinol-derivatives of gallocatechin and catechin, respectively, had the lowest and highest RMA.
3. Examination of the chemical structures and the antimutagenic activities of these polyphenolic products from kaki-tannin revealed that a pyrogallol ring, a benzene ring having three adjacent phenolic hydroxyl groups, was re-confirmed to be essential in antimutagenic activity. Furthermore, it was found that the component with a pyrogallol ring attached at the 2 position of the flavanol C ring is more active as the antimutagenic substance than that linked at the 3 position in a form of gallic acid ester.
4. That expression of this activity was closely related to a system of DNA excision repair in Escherichia coli was implicated by using a mutant strain which lacked this particular repair system.
The data presented here indicate that kaki-shibu contains at least two types of UV-antimutagenic substances, a tannin-related component and an unknown compound. Thus, the astringent kaki fruit may be a new source of physiologically active compounds.
