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.