The vanillin assay would be most useful for determining
proanthocyanidins if it could be carried out under conditions
where reaction occurs either at all of the &van-3-01
units of the polymer or only at the terminal units. The
first condition, which is usually assumed in using the assay,
would result in equivalent values for all proanthocyanidins
on a weight basis. The second condition would result in
equivalence on a molar basis. The data in Table I show
that in methanol, the conventional solvent for this reaction,
neither condition holds. Methanol, in fact, profoundly
inhibits chromophore production in this reaction, and
addition of small amounts of methanol result in rapid color
loss (Figures 1 and 2). Furthermore, methanol affects the