Peroxide value (PV)
Depending on the extent of peroxidation, 0.01 – 0.30 g of the oils were mixed in a disposable glass tube with 9.8 ml of chloroform–methanol (7:3 v/v) and vortexed for 2 – 4 s. Ammonium thiocyanate solution (50 ml, 30% w/v) was added and the sample was vortexed for 2 – 4 s. Fifty ml of iron(II) chloride solution ([0.4-g barium chloride dihydrate dissolved in 50-ml H2O] + [0.5-g FeSO4. 7H2O dissolved in 50-ml H2O] + [2-ml 10 M HCl, with the precipitate, barium sulfate, filtered off to produce a clear solution]) were added, and the sample was vortexed for 2 – 4 s. After a 5-min incubation at room temperature, the absorbance was read at 500 nm against a blank containing all the reagents except the sample. Results were expressed in meq of oxygen per kg of oil (Shantha and Decker, 1994).