177 Detection of Tannin Sorghum Grain by the Bleach Test

Methods Type: Generic Methods
Key data
Number: 177
Analyte: Tannin
Matrix: Sorghum
Year of Approval: 2012
Scope: Applicable to whole grain sorghum.
Principle: Sorghum grain is immersed in a sodium hypochlorite solution (bleach) containing alkali. The solution dissolves away the outer pericarp layer of sorghum grain, revealing the presence of a black pigmented testa layer in the case of tannin sorghums, or its absence in the case of non-tannin sorghums.


Certain varieties of sorghum contain proanthocyanidins (commonly referred to as tannins or more strictly-speaking condensed tannins) in the seed coat layer beneath the pericarp (commonly referred to as the testa layer) of the grain. These varieties are variously referred to as: tannin, high-tannin, brown, bird-proof, bird-resistant, or bitter sorghums.

Varieties of sorghum not containing tannins are various referred to as: non-tannin, low-tannin, condensed tannin-free, or sweet sorghums.

In this Standard the term “tannin sorghum” shall be used for those sorghums containing tannins and the term “non-tannin sorghum” used for those sorghums not containing tannins.


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