Evaluation of Vanillin Assay for Tannin Analysis of Dry Beans

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Abstract
Several parameters that might influence the vanillin assay for tannin analysis of dry bean (Phaseolus vulgatis L.) varieties were investigated. The assayable tannin content decreased with decreasing particle size of the bean flours. Time elapsed after grinding as well as storage under high humidity conditions markedly influenced tannin assays. The solubihty of tannins was dependent on the type of solvent used, with methanolic extraction requiring shorter periods as compared to extraction with acidified methanol. Color differences within the bean samples appeared to be the prime cause of variation in tannin analysis of beans. Extractions on seed coats alone increased the assayable tannin by 1.1‐2.5 times compared to extractions of bean flours.