The odor of fish oil is the major factor limiting its application in food. In this study, the addition of butylated hydroxytoluene to fish oil did not significantly inhibit the generation of fishy and rancid odors. To reduce the undesirable odors, fish oil was treated with lipoxygenase (LOX) to produce volatile compounds via position-specific cleavage of hydroperoxides. An extract of a green marine macroalga, Ulva conglobata, showed a high level of 13-LOX activity and 9-LOX to a lesser extent, and produced strong green, melon-like, and fresh-fishlike flavor notes from fish oil. The LOX-modified fish oil contained 99% of the highly unsaturated fatty acids (HUFA; containing three or more double bonds) originally present, total volatile compounds increased from 3477 to 3787 ppb after LOX treatment. Compounds with strong odors accounted for about 40% of the total volatiles. Increasing the level of LOX activity used to treat fish oil produced higher concentrations of the desirable unsaturated aldehydes, ketones, and alcohols, with odors resembling fresh fish, apple, citrus, melon, fruit, and oyster. These compounds were tentatively identified as E, Z-2,6-nonadienal, E-2-hexenal, E,E-2,4-octadienal, E,E-3-5-octadien-2-one, and alcohols E-2-pentenol and 2-butoxyethanol. The LOX treatment also slightly increased the content of the undesirable volatile components, including sour and rancid odors, tentatively identified as acetic acid and E,Z-and E,E-2,4-decadienals.
