Streamlined and rapid spectrophotometric method for determination of peroxide value in highly pigmented marine oils containing astaxanthin

Abstract

The International Dairy Federation (IDF) spectrophotometric method for measuring peroxide values (PV) was successfully modified for application to highly pigmented oils containing carotenoids. The standard method involves the oxidation of Fe(II) to Fe(III) ions by peroxides, which then react with thiocyanate to form a pink complex with maximum absorbance at 500 nm. For oils containing natural carotenoids and other reddish pigments that absorb in the same wavelength range, direct application of the method results in overestimated PV values. To address this issue, carotenoids were removed prior to absorbance measurement through a single methanolic extraction step. This yielded a lower organic phase containing carotenoid pigments and an upper methanolic phase with the thiocyanate-Fe(III) complex. The latter was then measured, and a cumene hydroperoxide calibration curve was used to quantify the lipid hydroperoxide content. The modified IDF method was validated using unpigmented oils (chia, sunflower, soy) with different degrees of oxidation and compared with the AOAC official iodometric titration method, showing good correlation. Additionally, the modified method demonstrated linearity, accuracy, and repeatability. It required shorter incubation times (10 min), smaller amounts of lipid samples and just one simple extraction step to determine PV in high carotenoid pigmented oils.