Carbonyl value (CV)
The spectrophotometric method developed by Endo et al. (2001) was used to determine the CV of the oils. 2-Propanol and 2,4-decadienal were used as solvent and standard, respectively. The oil samples (0.04 – 1.0 g) were diluted to 10 ml by distilled 2-propanol. One ml of the solution was introduced into a 15-ml test tube containing 1 ml of 2,4-dinitrophenylhydrazine (DNPH) solution (50 mg of DNPH in 100 ml of 2-propanol containing 3.5 ml of 37% HCl) as an indicator and 8 ml of %2 KOH. After centrifugation (2000×g, 5 min), absorbance of the upper layer was read at 420 nm.