Malonaldehyde/Gas Chromatography (MA/GC) Assay. A
detailed description of this assay was also previously reported.3 The
antioxidant activity was also determined by analyzing MA formed from
cod liver oil upon oxidation after derivatizing to 1-methylpyrazole (1-
MP) with N-methylhydrazine (NMH). An aqueous solution (5 mL)
containing 10 μL of cod oil, 0.25 mmol of trizma buffer (pH 7.4), 5
μmoL of ferrous chloride, 10 μmoL of hydrogen peroxide, 0.75 mmol
of potassium chloride, and 0.2% sodium dodecyl sulfate was incubated
with various amounts of the volatile extracts (prepared by sequentially
diluting the standard extract with ethanol) and their components
(authentic chemicals) for 18 h at 37 °C in a 20 mL test tube. The
oxidation was stopped by adding 50 μL of a 4% BHT solution. The
sample tubes were covered with aluminum foil during incubation to
avoid any influence of light on the lipid peroxidation. The control was
prepared from the same solution without a testing sample. The known
antioxidant BHT was used to validate the assay. The antioxidant
activity (%) was calculated using the following equation