Cereal Chem 58:234 - 238.  |  VIEW ARTICLE
Evaluation of Several Methods to Determine Tannins in Sorghums with Varying Kernel Characteristics.

C. F. Earp, J. O. Akingbala, S. H. Ring, and L. W. Rooney. Copyright 1981 by the American Association of Cereal Chemists, Inc. 

Polyphenols (tannins) in 21 sorghum cultivars with differing pericarp color and presence or absence of a pigmented testa were analyzed by seven methods: Prussian blue, vanillin hydrochloric acid (V-HCl) with and without blanks (20-min extraction), modified vanillin hydrochloric acid (MV-HCl) with and without blanks (20-min extraction), MV-HCl (24-hr extraction), and alpha-amylase inhibition. Subtraction of blanks in the V-HCl and MV-HCl procedures reduced the overall level of polyphenols measured without changing the relative quantities. Significant levels of polyphenols and amylase inhibition were found only in those cultivars with a spreader gene and a phenotypically brown pericarp, whether the pericarp was genetically red or white. When the methods were used to measure polyphenols in the sorghums with a brown pericarp, coefficients of variation (CV) were 9.5, 8.0, 8.2, 11.2, and 13.0% and F values with 9 and 14 degrees of freedom (df) were 105.8, 206.6, 191.5, 149.9, and 72.4 for Prussian blue, V-Hcl with blanks, V-HCl without blanks, MV-HCl with blanks, and MV-HCl without blanks, respectively. The CV was 2.7% and the F value with 8 and 7 df was 1735.71 for MV-HCl (24-hr extraction). The CV was 25.3% and the F value with 10 and 21 df was 20.60 for the alpha-amylase inhibition method. Correlations among methods ranged from 0.85 to 0.99. The MV-HCl (24-hr) had the highest F value and lowest CV but is not recommended because of the long extraction period. The V-HCl method with or without blanks is recommended as the most reliable for analyzing polyphenols in sorghum because they have the next highest F values and lowest CV. The method with the highest F value should be the most sensitive to detecting levels of polyphenols due to genetic variation.