Elucidating the thermal degradation of fish oil and algal oil: A comparative study on the evolution of flavor profiles and lipid oxidative pathways.

As a major source of essential polyunsaturated fatty acids, fish oil faces increasing sustainability constraints, underscoring the need for viable lipid alternatives. Volatile organic compounds and lipidomic transformations of fish oil (FO) and algal oil (AO) were characterized. In both oils, aldehydes, ketones, and alcohols constituted the predominant classes, and their relative proportions were broadly comparable. As oxidation temperature increased, FO and AO displayed similar trends in flavor development and lipid compositional changes. FO preferentially developed fatty-green and roasted notes dominated by aldehydes, benzenoids, and furans. AO exhibited a broad and complex flavor profile enriched in alcohols, ketones, sesquiterpenoids, and indole derivatives, imparting enhanced herbal, fruity, and floral characteristics during thermal processing. Volatile formation in FO was dominated by phospholipid oxidation, yielding key markers such as (E)-2-nonenal and (Z)-3-hexenal. Triacylglycerol oxidation predominated in AO, producing characteristic compounds including (E, E)-2,4-nonadienal and 2-methylbutanal. Despite distinct oxidation mechanisms, both oils exhibited comparable thermal flavor evolution, supporting algal oil as a sustainable and vegetarian-friendly alternative to fish oil.