Aliquots from the Cu2+ oxidized samples treated with
PF from the three oils were tested for carbonyl formation.
To the samples, 0.5 ml of 2, 4-dinitrophenyl hydrazine (10
mM in 2N HCl) was added and was allowed to react for
60 min at room temperature with vortexing every 15 min.
After the reaction was complete, 20% TCA (0.5 ml) was
added and the samples were centrifuged. The precipitate
was washed with ethanol/ethyl acetate (1:1), dissolved in
0.6 ml of guanidine (6 M in phosphate buffer, adjusted to
pH 2.3 with trifluoroacetic acid) and incubated at 37jC for