Value added fish by-products - Nordic Innovation

(minced cod fillet, which were kept in the freezer and defrosted overnight at 4 o C). A low
speed centrifugation method was used for measuring the WHC as described by Eide et al.
(1982) with the exception that a centrifugal force of 300*g was used instead of 1500*g. The
WHC is expressed as the water retained in the mince in percentage of the original water. The
test was performed in quadruplicate.
2.3.1.7 Determining antioxidant activity
The antioxidative activity of FPH was determined using an indirect spectrophotometric assay,
the DPPH method as described by Thiansilakul et al. (2007). Liposomes have been proposed
to be an appropriate model system to evaluate antioxidants for food (Frankel et al. 1997).
Due to this, the antioxidant activity of FPH was also evaluated in a liposome model system
using iron as prooxidant.
2.3.1.7.1 Determining antioxidant activity using liposomes
In some food products lipids exist in the form of small fat droplets dispersed in an aqueous
matrix that may contain a variety of water-soluble components including transition metals
Ghaedian et al. 1998. Among the transition metals, iron is one of the most important pro-
oxidants for lipid oxidation (Paiva-Martins & Gordon 2002). Iron catalyse lipid oxidation due
to its capacity to generate reactive oxygen species promoting breakdown of lipid
hydroperoxides, which leads to an initiation of free-radical chain reaction (Minotti & Aust
1992). The antioxidant activity of hydrolysates was determined using cod roe phospholipid
liposomes. The phospholipids used in these experiments were isolated from North Atlantic
cod (Gadus morhua) roe. The extraction of total lipids was performed according to the
method of Bligh & Dyer (1959). Phospholipids were isolated from total lipids using the
acetone precipitation method Kates 1991, with a few modifications as described by
Mozuraityte et al. (2006).
Liposomes were made as described by Mozuraityte et al. 2006. Phospholipids were sonicated
in a 5mM MES buffer pH 5.5 (lipid concentration 30mg/ml) with a probe sonicator (VC501,
Sonics & Material Vibra Cell, USA).
Lipid oxidation was performed in a liposome assay containing 6mg/ml phospholipids and
Fe 3+ was used to generate radicals. The consumption of dissolved oxygen by liposomes in a
closed, stirred, water jacketed cell was used as a measure of lipid oxidation. The
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