Docosahexaenoic acid (DHA) has been shown to be essential for normal brain and retinal development. Effects of refining, bleaching, winterizing, and deodorizing on the oxidative stability of DHA (22:6 Ω-3) oil were studied by a combination of headspace oxygen depletion (HOD) by gas chromatography and total volatile compound formation by SPME-GC. The oxygen content in the refined, bleached, winterized, and deodorized DHA oil samples decreased from 20.9% on Day 0 to 6.7%, 8.3%, 7.8% and 7.8%, respectively on Day 5. The bleached, winterized, and deodorized oils were determined not to be statistically different from each other (p > 0.05), however the refined oil showed significantly more HOD (p <0.05), corresponding to a lower oxidative stability. Refined, bleached, winterized, and deodorized oils showed average volatile compound formations over 5 days of storage of approximately 4,041,000 electronic counts (ec), 482,100 ec, 437,200 ec, and 405,800 ec, respectively. The refined samples again showed significantly (p < 0.05) higher volatile compound formation, corresponding to a lower oxidative stability. The bleached, winterized, and deodorized samples were not significantly different from each other (p > 0.05). Bleaching proved to be the crucial processing step in increasing the oxidative stability of DHA oil.
Ginseng has been shown to be a natural antioxidant, and compounds from its extract are studied here for their individual antioxidant effects. Kaempferol, caffeic acid, ferulic acid, salicylic acid, and vanillic acid were previously isolated, separated, and identified by the combination of HPLC, NMR and MS. The effects of 100 ppm of each compound on the riboflavin photosensitized oxidation were studied at 4°C for 3 hours. Additionally, the effects of 100 ppm of each compound on the autoxidation of linoleic acid was studied, both with and without added ferrous chloride to give 2 ppm ferrous ion at 37°C in the dark for 10 days (with ferrous ion) or 40 days (without ferrous ion). The HOD of the samples was determined by GC and the peroxide value by spectrometry. Caffeic acid, kaempferol, vanillic acid, salicylic acid, α-tocopherol, and ferulic acid minimized the photosensitized oxidation by 37, 30, 30, 18, 17, and 0%, respectively. The average peroxide value for linoleic acid in aqueous solution without 2 ppm ferrous ion and 100 ppm kaempferol, vanillic acid, ferulic acid, caffeic acid, salicylic acid, α-tocopherol or control during 40 days of storage was 0.2, 0.7, 2.2, 2.3, 2.7, 2.8, or 3.7, respectively. The average peroxide value for samples with 2 ppm ferrous ion and 100 ppm kaempferol, vanillic acid, ferulic acid, caffeic acid, α-tocopherol, salicylic acid, or control during 10 days of storage was 0.3, 1.2, 2.5, 2.8, 5.3, 6.3, or 7.5, respectively. Ginseng compounds did not have antioxidant effects in the photosensitized oxidation of 2% linoleic acid in the aqueous system at p>0.05. Ginseng compounds except salicylic acid had better antioxidant effects than α-tocopherol in the autoxidation of linoleic acid in the aqueous system at p< 0.05. Caffeic acid, ferulic acid, and vanillic acid may act as antioxidants by the combination of donating hydrogen atom and chelating ferrous ion.