Ho

Figure 3. Formation of proanthocyanidins.

Proanthocyanidin

Cation

Catechin

Figure 3. Formation of proanthocyanidins.

Proanthocyanidin

In other food products enzymic browning may be disadvantageous. It can be prevented by enzyme inactivation (often blanching), by the use of antioxidants, or by the rigorous exclusion of oxygen. Wine technology is largely an exercise in tannin control (6). White wine production is managed so as to exclude the polyphenol-rich grape skins and seeds from the juice in order to minimize enzymic browning. Pro-cyanidins are present at about 10 mg/L and may be desirable at this low level. Red wine is produced so as to include phenolic components in the fermenting juice. Final pro-cyanidin content is in the range of 40 to 65 mg/L. Color changes that occur during the aging of red wine include the diminution of the original color (primarily from anthocya-nins) and the formation of new, more stable, oligomeric pigments (8). Procyanidin dimers in beer originate from the malt and are troublesome haze formers. The tannins involved are primarily dimers of catechin and epicatechin (9).

Fruit, vegetables, grain, and many beverages are sources of condensed tannins in the diet as shown by a few examples in Table 1.

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