Agriculture Reference
In-Depth Information
Potassium Hydroxide (koH) Test for red rice (
Oryza sativa
)
Due to the variation in emergence and maturity of red rice and the time required for the development of the
red coloration on the grain, it is possible for colorless or nearly colorless seeds of red rice to contaminate
rice seed lots. A simple KOH soak test for the detection of red rice seed was originally developed by Rosta
(1975). This test was modiied to be used in conjunction with the current laboratory procedure of hulling a
sample of seed rice to check for the presence of red rice caryopses. Suspect seeds can be selected from the
hulled sample and tested for conirmation.
Procedure
1. Place seeds to be tested in a small test tube and add two drops of a 2.0% KOH solution (2.0 g
KOH/100 ml H
2
O). Red rice seeds will cause the KOH solution to develop a deep red color within
3 to 10 min (Fig. 9.12). Standard rice cultivars will appear a light golden yellow in solution. Check
samples may be used for color conirmation.
2. Older seeds of red rice (e.g., carry-over lots) may require as long as 30 minutes for color develop-
ment. The KOH solution should be kept sealed and refrigerated. Do not use solutions more than
two weeks.
Figure 9.12. The potassium hydroxide (KOH) test for red rice: seed rice (top), red rice (bottom).
Potassium Hydroxide (koH) Test for Sorghum (
Sorghum
spp
.
)
The presence or absence of a darkly pigmented testa or undercoat layer can be used to help differentiate
sorghum cultivars. Tannic acid has been identiied as the dark pigment layer in the testa. High tannic acid
content is undesirable for animal feed, while it repels foraging birds. This has led to cultivars with varying
tannic acid content, depending on end use.
