2-Thiobarbituric acid (TBA) is used as a reagent to indicate rancidity of foods which contain polyunsaturated fatty acids.
It condenses with malonaldehydes (an oxidation product of linoleate) producing a pink colour, and also reacts with aldehydes and dienals, giving orange colours. This test, which gives the best results for foods that contain polyunsaturated fatty acids, was used by previous researchers to indicate the edibility of nuts (Faruk Gamli & Hayoglu, 2007).