Effects of food structure and ingredient interactions on antioxidant capacity - Oxidation in Foods and Beverages and Antioxidant Applications - page 323

expected to accelerate lipid oxidation. This phenomenon has been exploited in
the Active Oxygen method and the Rancimat method for assessing oil stability.
However, the dynamic passage of air through the oil is very different from the
situation in stored foods. Volatile antioxidants and lipid oxidation products are
swept from the sample in these assays, and this can have dramatic effects on
oxidative stability.
13.3 Effect of nature of the lipids and the medium
The nature of the lipids has an important effect on the effect of antioxidants on
the susceptibility of foods to oxidation. In products such as meat and fish,
oxidation of phospholipids is an important source of off-flavours (Jittrepotch et
al., 2006). Simpler iron species originating from degradation of heme proteins
and other sources bind to negatively charged phospholipids in membranes and
catalyze the cleavage of preformed lipid hydroperoxides. Heme initiated lipid
peroxidation, is important for quality deterioration of muscle-based foods
(Carlsen et al., 2005). The -tocopherol content of membranes is an important
variable that affects the oxidative stability of the membranes, and the importance
of -tocopherol in ensuring the stability of muscle membranes is particularly
high in muscles that are richer in polyunsaturated fatty acids (Yang et al., 2003).
Liposomes are often used as models for phospholipid membranes. Liposomes
may be either unilamellar or multilamellar in structure, although the unilamellar
structure is a better model of a biological membrane. The multilamellar
liposome contains successive shells of phospholipid bilayers separated by
aqueous compartments, whereas the unilamellar liposome contains a single
phospholipid bilayer with an internal aqueous compartment (Fig. 13.3). Both
Fig. 13.3 Structure of a unilamellar liposome particle.