Quality Differences Among Fish- and Algae-Derived Omega-3 Supplements: Insights from Physicochemical, Oxidative, and Thermal Analyses

Omega-3 long-chain polyunsaturated fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are widely consumed due to their recognized health benefits. Consequently, dietary supplements containing fish oil or algae-derived oils have become increasingly popular. However, the high susceptibility of polyunsaturated fatty acids to oxidation raises concerns regarding the quality and stability of such products. This study aimed to comprehensively evaluate the physicochemical quality, oxidative stability, thermal behavior, and fatty acid composition of omega-3 dietary supplements available on the Polish over-the-counter market, with particular emphasis on differences between fish- and algae-derived products. Twelve supplements were analyzed, including eight fish oil-based and four algae-derived formulations. Fatty acid composition was determined by gas chromatography (GC), oxidative stability by pressure differential scanning calorimetry (PDSC), and melting characteristics by differential scanning calorimetry (DSC). In addition, acid value (AV), peroxide value (PV), p-anisidine value (p-AnV), and total oxidation index (TOTOX) were measured. Fish oil supplements contained both EPA (17.50–38.76%) and DHA (13.42–36.83%), whereas algae-derived products were characterized by high DHA content (36.83–62.79%) and low EPA levels. Oxidative stability varied markedly among samples, with oxidation induction times ranging from 6.73 to 18.71 min. TOTOX values ranged from 11.57 to 36.43, indicating substantial differences in oxidative quality. Thermal analysis further revealed distinct melting behaviors associated with lipid composition. This study provides a comprehensive comparison of fish- and algae-based omega-3 supplements, integrating compositional, oxidative, and thermal analyses with technological factors such as packaging and antioxidant systems. The results highlight considerable variability in the quality of commercially available products and emphasize the importance of multidimensional analytical approaches for reliable evaluation of omega-3 supplements.