where AM, AD, and AN represented the absorbance of the mixture solution, the damaged and non-damaged 1,10-phenanthroline solution, respectively.
2.8. Linoleic acid autoxidation (LAAO) inhibition activity assay
A slightly modified ferric thiocyanate (FTC) method (Kikuzaki & Nakatani, 1993) was used to determine the LAAO inhibition activity. The assay system was as follows: a mixture of 1.0 mL of 1.4 mg/mL PSPA sample or VC, 1.0 mL of 2.5% (v/v) linoleic acid, 2.0 mL of 0.05 M PBS (pH 7.0) and 1.0 mL of water was placed in a tube and incubated in an oven at 40 °C in the dark. The degree of linoleic acid oxidation was evaluated by measuring the FTC values. The following reagents were added to a 0.1-mL aliquot of the above mixture: 4.7 mL of 75% ethanol, 0.1 mL of 30% ammonium thiocyanate, and 0.1 mL of 20 mM ferrous chloride solution in 3.5% hydrochloric acid. A blank solution was prepared by adding the same volume of water instead of sample. The mixture was incubated at 40 °C and the absorbance measured at 500 nm every 24 h until the absorbance reached a maximum (96 h). The FTC value was calculated as: