Abstract
The aims of this study were to investigate the role of hemoglobin (Hb) in lipid oxidation development during ensilaging of herring filleting co-products, and, to inhibit this reaction by pre-incubating the co-products in water or physiological salt, with/without different antioxidants. Results showed that both peroxide value (PV) and 2-thiobarbituric acid reactive substances (TBARS) gradually increased during 7 days of ensilaging at 22 °C in absence of antioxidants. The increase in TBARS was proportional to the Hb levels present, while PV was less affected. A Hb-fortified Tris-buffer model system adjusted to pH 3.50 confirmed that Hb changed immediately from its native oxyHb to the metHb state, which facilitated heme group release and thus probably explains the increased PV and TBARS during ensilaging. Pre-incubating the co-products for 30 s in a solution containing 0.5% rosemary extract was the most promising strategy to inhibit lipid oxidation both in the co-products during pre-processing storage and during the actual ensilaging. The solution could be re-used up to ten times without losing its activity, illustrating that this methodology can be a scalable and cost-effective strategy to extend the oxidative stability of herring co-products allowing for further value adding e.g., into a high-quality silage.
Highlights
The aims of this study were to investigate the role of hemoglobin (Hb) in lipid oxidation development during ensilaging of herring filleting co-products, and, to inhibit this reaction by pre-incubating the co-products in water or physiological salt, with/without different antioxidants
In case of thiobarbituric acid reactive substances (TBARS), significantly (p < 0.05) higher levels were noticed after 2 days and 1 day of ensilaging in 2- and threefold Hb-fortified samples, respectively, compared to the controls, and the difference between fortified and control samples gradually increased throughout the studied period (Fig. 1C,D)
Contrary to peroxide value (PV)-data, a higher level of TBARS was noticed in the sample with threefold Hb-level, compared to the one with twofold Hb-level, i.e. 1954.96 vs. 1777.02 μmole TBARS/kg, respectively, after 7 days of ensilaging
Summary
The aims of this study were to investigate the role of hemoglobin (Hb) in lipid oxidation development during ensilaging of herring filleting co-products, and, to inhibit this reaction by pre-incubating the co-products in water or physiological salt, with/without different antioxidants. To minimize Hb-mediated lipid oxidation during processing of fish, several strategies have been reported to date, e.g. use of phytic acid to precipitate Hb during pH-shift processing of cod muscle[12], increasing the pH of fish muscle minces to avoid Hb-deoxygenation and met-Hb formation[10], and washing of fish mince such as in surimi p roduction[13]. These reported strategies are not compatible with e.g. large-scale ensilaging of fish filleting co-products, calling for further developments. The effectiveness of such to minimize lipid oxidation during subsequent ensilaging of herring co-products at pH ~ 3.50 has never been reported, but we hypothesize that the reduction in Hb-levels and introduction of antioxidants would substantially elevate the silage quality
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