Peroxide value (PV)
A ferric-thiocyanate based spectrophotometric assay was used as
previously reported (Shantha & Decker, 1994) for the determination of
PV, with the following modifications: the assay volume was
proportionally reduced to 3.0 ml, oil sample size was reduced to 10 mg,
and a mixture of methanol/isopropanol (2:1 v/v) was used as the solvent
to avoid using chloroform. Absorbances were measured using a PerkinElmer
Lambda 35 UV/Vis spectrophotometer (Perkin Elmer, Waltham, MA, USA) at
510 nm. Ferric chloride solutions (1-15 µg Fe3+/ml) in
methanol/isopropanol (2:1 v/v) were used for the standard curve. Three
experimental replicates were analyzed in duplicate.