Figure 6. Oenthein A and Woodfordin D.
the grain and soaking in dilute formaldehyde are also effective procedures for improving its nutritional value.
The polyphenolic content of the tannins imparts antioxidant activity to biological systems. The ability of condensed tannins from several plant sources to scavenge oxygen-containing free radicals has been demonstrated (23). Exploitation of this effect to produce beneficial consequences for humans has been suggested since peroxidation has been implicated in tumerogenesis. Some di-meric ellagitannins exhibit antitumor activity in mice. Structure and activity have been correlated (23). It has been suggested that possible mechanisms for pharmacological activity of tannins may depend on several tannin propensities: complexation with transition-metal ions; free-radical quenching; complexation with proteins and peptides (25).
Inhibition of tumor growth in rodents by the administration of some oligomeric hydrolyzable tannins after intraperitoneal inoculation of tumor cells has been observed. Examples of these active ellagitannins are oenothein and woodfordin, shown in Figure 6. This effect is an example of host-mediated antitumor activity as interleukin-1 is induced in the treated animals (26,27).
Life expectancy of stroke-prone hypertensive rats has been extended by feeding persimmon tannin. Grape seed procyanidin exhibits anti-inflammatory activity in experimental animals. (28).
Some selected purified tannins have been tested and shown to be nonmutagenic by the Ames Test (29).
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