The concentrations and pro‐oxidative effects of free fatty acids in commercial krill oil are not well defined. We now report that krill oil free fatty acids account for 2–13% of total lipids in commercial krill oil (n = 8) that these compounds are enriched in eicosapentaenoic acid (+7.1%) and docosahexaenoic acid (+6.3%) relative to whole oils; and that this composition make them highly pro‐oxidizing in marine triacylglycerol oils, but not in krill oil, which derives oxidative stability from both its phospholipids, and neutral lipids (the latter because of astaxanthin). Specific fatty acid esterification patterns showed that krill oil free fatty acids predominantly (88–93%) originated from phospholipids, mainly from the sn‐2 position, which was eight‐fold more hydrolyzed than the sn‐1 position. Lipolysis was not ongoing in stored oils. Adding small amounts of krill oil (1–5%) to marine triacylglycerol oils significantly increased their oxidative stability and also their resistance to free fatty acid‐mediated pro‐oxidative effects.

Krill oil contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), long chain omega-3 polyunsaturated fatty acids with essential roles in human health, and astaxanthin, a naturally occurring keto-carotenoid that protects EPA+DHA against oxidation. Here, we assess Raman and IR spectroscopy (as stand-alone techniques and paired using three different data-fusion approaches) as methods for simultaneous quantitation of EPA+DHA and astaxanthin in krill oil. Raman spectroscopy could accurately (RMSEP = 40 μg g–1, r 2 p = 0.98) quantitate astaxanthin in krill oil despite its low concentrations (212–693 μg g–1). This analysis could be performed directly through gelatin capsules with no loss of prediction accuracy (RMSEP = 27 μg g–1, r2 p = 0.99). Fusing IR and Raman data did not improve the astaxanthin quantitation models. EPA+DHA quantitation was more accurate using “mid-level” fusion (RMSEP = 1.2%, r 2 p = 0.99) than models from either Raman (RMSEP = 4.5%, r 2 p = 0.90) or IR (RMSEP = 7.3%, r 2 p = 0.73). Data fusion also significantly improved quantitation accuracy for quantification of other fatty acid classes.

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Raman and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy were used to analyse seven krill oil capsules and twenty-five calibration samples to quantitate astaxanthin, EPA plus DHA and other important fatty acids. Spectroscopic data was calibrated against FAME profiles (measured by GC-MS) and astaxanthin concentrations (measured by UV-VIS). Raman spectra was found to be suitable to quantify astaxanthin, EPA, DHA and EPA + DHA, with reasonable root mean square error of prediction (RMSEP) for test set validation: 40 μg g-1 , 2.5%, 2.2% and 4.5% respectively.