These tests all indicate an increase in protein binding activity from
the milk through the dough stages. This is analogous to the results
of the chemical reactivity tests discussed earlier and is probably due
to synthesis of tannin molecules of the appropriate size and shape for
binding. With the exception of the protein binding test, tannin
activity apparently decreases at maturity.

Group II sorghum evaluations: Sorghums can be categorized into three
groups (I, II, or III) on the basis of their polyphenolic values as
determined by two vanillin tests. When the 15 varieties that we are
working with were classified in this manner, two were low tannin
(group I), four were intermediate tannin (group II), and nine were
high tannin (group III). We found that a similar categorization can
be made by Sephadex LH-20 chromatographic analysis. Researchers at
Purdue University have observed that group-II sorghums have excellent
nutritional qualities and our chromatographic profiles showed that
these same varieties were quite different from the others. Thus, our
interest became focused on the group-II sorghums. We hypothesized
that during maturation the polymerization process to large, unreactive
molecules is more complete in those varieties but that tannin mole-
cules might be of the appropriate size to produce astringency during
the milk and dough stages.

Vanillin, Folin-Denis, leucoanthocyanin, and protein precipitation
analyses were conducted on all 15 varieties to compare the properties
of groups I, II, and III. These results, along with chromatographic
data and Quelea preference are given in Table 16.

All of the group-II values are similar to those of group I but quite
different from group III. These findings are comparable to Purdue
University's nutritional comparisons.

The Vanillin/Folin-Denis and Vanillin/leucoanthocyanin ratios indicate
that these differences may be attributable to formation of a greater
proportion of large inactive molecules during maturation in the
group-II sorghums than in the group-III varieties. Extraction
studies indicate that several other factors may also contribute to
the differences. These include (1) the influence of molecular shape
on cell wall binding, (2) differences in cell wall structure, or (3)
differences in tannin shape and composition.