Changes in headspace volatiles and peroxide values of undeodorized menhaden oil over 20 weeks of storage

Undeodorized menhaden oil was stored in the dark at 30 degrees C under a headspace of air. Oil samples were removed at 0, 1, 2, 3, 4, 8, 12, 16, and 20 weeks of storage and analyzed for peroxide value and headspace volatiles by GC and GC-MS. Total volatiles increased in concentration during the first 2 weeks of storage, fell slightly at week 3, and then rose steadily reaching a second maximum at week 16, before declining again at week 20. Peroxide values exhibited three maxima, at weeks 1, 4, and 12. Several volatiles that are potentially derived from lipoxygenase activity in menhaden were identified in the oil including 1-penten-3-ol, (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-octenal, 1-octen-3-ol, 2,5-octadien-1-ol, 2-nonenal, and (E,Z)-2,6-nonadienal. Some volatiles derived from autoxidation are as follows: (E,E)-2,4-heptadienal, (E,Z)-2,4-hepadienal, (E,E)-2,4-decadienal, and (E,E)-3,5-octadien-2-one. Five of these volatiles reached maximum concentrations by the first or second week of storage. These findings suggest that pro-oxidant mechanisms at work prior to and/or during oil refining lead to rapid buildup of objectionable flavors and aromas in menhaden oil.