Modification of fish oil aroma using a macroalgal lipoxygenase

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 prod uce volatile compounds via positibn-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-modifie d fish oil contained 99% of the highly unsaturated fatty acids (HUFA; conta ining three or more double bonds) originally present, total volatile compou nds increased from 3477 to 3787 ppb after LOX treatment. Compounds with str ong odors accounted for about 40% of the total volatiles. Increasing the le vel of LOX activity used to treat fish oil produced higher concentrations o f the desirable unsaturated aldehydes, ketones, and alcohols, with odors re sembling fresh fish, apple, citrus, melon, fruit, and oyster. These compoun ds were tentatively identified as E,E-3,6-nonadienal, E-2-hexenal, E,E-2,4- octadienal, E,E-3-5-octadien-2-one, and alcohols E-2-pentenol and 2-butoxye thanol. The LOX treatment also slightly increased the content of the undesi rable volatile components, including sour and rancid odors, tentatively ide ntified as acetic acid and E,Z- and E,E-2,4-decadienals.