Lipid hydroperoxides (LH)

As the marker of the primary products of lipid oxidation, LH was determined according to the reported method with some modifications (Huang et al., 2019). Emulsified RCOO-RCOPPs (0.3 mL) were mixed with 1.5 mL of a 2-propanol and isooctane (1:3, v/v) solvent mixture and vortexed for 2 min, and then the mixture was centrifuged (4000 g RCF, 5 min). The organic phase (0.2 mL) was added to 2.8 mL of a methanol and 1-butanol mixture (2:1, v/v), followed by adding 50 μL of 3.94 mol/L NH₄SCN solution and 50 μL of Fe²⁺ solution, which was produced by mixing a 0.132 mol/L BaCl₂ solution with 0.144 mol/L FeSO₄. After 20 min of dark reaction at room temperature, the absorbance of the obtained solutions was measured at 510 nm, and the PV value in the emulsion can be calculated according to equation (2) (Li, Jiang, Zhang, Mu, & Liu, 2008).

PV represents the peroxide value (meq/kg) in the sample. A represents the absorbance of the sample. K represents the slope of the Fe³⁺ calibration curve. 0.5 represents the molar ratio of O/Fe. 55.86 represents the atomic weight of Fe. The division by factor 2 is essential to express the peroxide value as milliequivalents of peroxide instead of milliequivalents of oxygen (Shantha & Decker, 1994).