SOP: Kreis Test for Rancidity

GIFSQ — Global Institute for Food Safety & Quality

Principle

The test depends upon the formation of a red colour when an oxidised fat is treated with conc HCl and a solution of phloroglucinol in ether. The compound in rancid fats responsible for the colour reaction is epihydrin aldehyde. All oxidised fats respond to the Kreis test, and the intensity of the colour produced is roughly proportional to the degree of oxidative rancidity.

Apparatus required

• Test tube

Reagents

a. Concentrated HCl.

b. 1% solution of phloroglucinol in diethyl ether.

Procedure

Mix 1 ml of melted fat and 1 ml of conc HCl in a test tube

↓

Add 1 ml of a 1% solution of phloroglucinol in diethyl ether and mix thoroughly with the fat–acid mixture

↓

A pink colour formation indicates that the fat is slightly oxidised, while a red colour indicates that the fat is definitely oxidised

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.