Vanillin-condensed tannin study using flow injection spectrophotometry

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.