We examined several parameters of the vanillin assay
for tannin in addition to those we previously investigated
(Price et al., 1978). A brief survey of vanillin (4-
hydroxy-3-methoxybenaldehyde) analogues demonstrated
that 2,4-dimethoxybenzaldehyde gave absorbance values
2-5 times greater than those obtained with vanillin and
may therefore warrant further investigation if greater
sensitivity is needed. All data presented in this paper were
obtained by using vanillin.
The rate and extent of color development in the reaction
between vanillin and catechin or tannin were found to be
strongly solvent dependent. Conventional solvents for this
reaction are sulfuric acid (Swain and Hillis, 1959) and
methanol (Burns, 1971). In both glacial acetic acid and
acetonitrile the reaction produced much more intense
absorption near 500 nm than was produced in methanol.
Glacial acetic acid was chosen for further investigation
because the kinetics of the reaction are less complex in this
solvent and the colored product is more stable.