| The purpose of this research was to investigate the efficacy of antioxidants for the suppression of off-flavors in fish oil emulsion and bulk fish oils. The antioxidant activity of selected polyols and nitrogen-containing compounds was determined using a model oil-in-water emulsion prepared with freshly deodorized menhaden oil and held under fluorescent light (2550 Lx) for 24 h at 5°C. In addition to a viscosity effect, polyols with high water solubility provided the greatest antioxidant activity, presumably by free radical scavenging and transition metal chelation. Also, phospholipids and polyols can participate in retro-aldo condensations by removing water from reactions and inhibiting the conversion of E,Z-2,4-nonadienal (green) to Z-4-heptenal (burnt fishy). Data also showed that incorporation of cysteine, histidine, or carnosine was effective in suppressing the formation of peroxides and off-flavored volatiles. The interaction of the hydroxyl radical with sulfhydryl or imidazole groups is proposed to account for at least part of the antioxidant activity of the compounds evaluated. Introduction of polyols into bulk fish oil by equilibrating excess polyols (10% by wt) at an elevated temperature (90°C) induced a notable degree of antioxidant protection. An antioxidant combination of TBHQ and lipoic acid at 21°C protected fish oil in the darkness from developing an unacceptable fishy-burnt flavor up to 1296 h (54 d), presumably by suppressing the formation of decatrienals isomers and their potentiator Z-4-heptenal. TBHQ-based antioxidant mixtures including polar antioxidants (sorbitol, cyteine, citric acid) in propylene glycol, conjugated linoleic acid (CLA), dilauryl thiodipropionate, and ascorbyl palmitate were introduced into freshly deodorized fish oil, which extended the flavor acceptability of fish oil up to 700 h under light 2550 (Lx) at 5°C. alpha-Tocopherol when added to fish oil along with other natural antioxidants, including cysteine, fructose, citrate, ascorbate, CLA, and lecithin and held under light, increased the flavor stability of the oils by 456 h and exhibited a pleasant celery-type flavor. The existence of green aroma compounds, presumably nonadiene isomers (IE 4.0 and 5.0) was confirmed in menhaden oil by olefactometry and gas chromatography-mass spectrometry. |
