Erroneous Thiobarbituric Acid Values in Fish Tissues Caused by Their Normal Content of Free Iron

Abstract

Erroneously high TBA values were obtained from liver, dark muscle, and certain other organs taken from seven species of sea fish. This error was eliminated by carrying out a portion of the test under anaerobic conditions or, more simply, by adding a mixture of EDTA and propyl gallate to the tissues immediately before the test is carried out. The error in the TBA values from the white muscle of lean fish and from whole cod fillets was found to be extremely small.By adding measured amounts of iron to white muscle immediately before testing it was found that from 1 to 20 ppm Fe++was sufficient to cause extensive errors in the TBA values. Schoenmakers and Tarladgis have recently reported that up to 5000 ppm Fe+++can be added to methyl linolenate and several vegetable oils without changing the TBA values. It is suggested that this apparent contradiction is the result of the differences in the substrates used. Marine oils contain more highly unsaturated fatty acids and the tissues contain other biologically active compounds capable of reacting with the oxidizing lipids.