Talanta 51 (2000) 1–6
Vanillin-condensed tannin study using flow injection
spectrophotometry
Edilene C. Ferreira
a
, Ana Rita A. Nogueira
b,
*
a
Departamento de Quı ´mica, Uniersidade Federal de Sa ˜o Carlos, P.O. Box 676, 13560 -970 Sa ˜o Carlos SP, Brazil
b
Centro de Pesquisa de Pecua ´ria do Sudeste, Empresa Brasileira de Pesquisa Agropecua ´ria, P.O. Box 339,
13560 -970 Sa ˜o Carlos SP, Brazil
Received 23 April 1999; received in revised form 6 July 1999; accepted 15 July 1999
Abstract
Studies involving the kinetic reaction between vanillin and condensed tannins were developed using a flow injection
system with spectrophotometric determination. A solution of the monomeric compound ( -)-epicatechin was used as
the analytical standard. This compound was chosen due to its structure, which is similar to a polymeric unit of the
condensed tannin present in plants. The results indicated that the vanillin – condensed tannin reaction is time
dependent and affected by the degree of polymerization of the condensed tannin. The flow system allowed
( -)-epicatechin to be used without overestimating the content of the tannin present in the forage legume, guandu
(Cajanus cajan (L.) Millsp.), studied. A relative standard deviation (R.S.D.) of 1% was found for a 4 h period work
and allowed the determination of about 60 samples h
-1
with a detection limit of 1.05 mg l
-1
for condensed tannin.
When compared to the manual vanillin procedure, the proposed approach can be used with various advantages.
© 2000 Elsevier Science B.V. All rights reserved.
Keywords: Flow injection; Guandu seeds; Spectrophotometry; Tannin
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1. Introduction
The term ‘tannin’ was used for the first time by
Seguin in 1796, to designate the bitter capacity of
oak to tan leather. Its presence in food reduces its
palatability and causes processing problems, such
as discoloration and haze formation [1]. The tan-
nins are defined as a heterogeneous mixing of
polyphenols of vegetable origin with high molecu-
lar weight. They are divided in two main groups:
the hydrolyzed and the condensed tannins. The
latter presents complex structures such as dimers,
trimers, oligomers and polymerics. Their basic
structures can be represented by the catechins,
antocianidins and flavones [2]. These compounds
have the property to bind with proteins [3–6]. The
complex tannin – protein is stable at physiologic
pH, and the presence of high concentrations of
condensed tannins can cause damage to the con-
* Corresponding author. Tel.: +55-16-2615611; fax: +55-
16-2615754.
E-mail address: anarita@cppse.embrapa.br (A.R.A.
Nogueira)
0039-9140/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII:S0039-9140(99)00222-2