Food Lipids: Chemistry, Nutrition, and Biotechnology

V. ALTERATIONS IN LIPID OXIDATION BREAKDOWN PRODUCTS
Oxidation of fatty acids eventually leads to formation of breakdown products via �scission
reactions. These reactions lead to a multitude of different oxidation products,
known as secondary lipid oxidation products, which affect both the sensory characteristics
and the functional properties of foods. Rancid odors arise from the production
of secondary products such as aldehydes, ketones, and alcohols [86]. Secondary
lipid oxidation products, and in particular aldehydes, also impact food quality
and nutritional composition through interaction with the amino groups of proteins
and vitamins. Secondary products arising from lipid oxidation have been found to
alter the function of proteins, enzymes, biological membranes, lipoproteins, and DNA
[80,87–89].
Since aldehydes and other secondary products arising from lipid oxidation are
potentially damaging, biological systems seem to have developed mechanisms to
control their activity. Sulfur- and amine-containing compounds have the ability to
interact with aldehydes. This may help explain why many proteins, peptides, amino
acids, phospholipids, and nucleotides display antioxidant activity when secondary
products are used to measure lipids oxidation. Carnosine and anserine, which can
make up over 1% of the wet weight of muscle tissue, are capable of forming complexes
with aldehydes produced from oxidizing lipids [90]. Carnosine is more effective
at forming adducts with aldehydes than its constituent amino acids, histidine
and �-alanine [91,92]. Glutathione is also very effective at binding aldehydes, but
at the concentrations found in muscle foods, carnosine seems more likely to be the
major aldehyde-binding component [92].
VI. SURFACE-ACTIVE ANTIOXIDANTS AND PHYSICAL EFFECTS
Lipids in food systems often have interfacial surfaces at which oxidative reactions
are prevalent. Examples include oil-in-water emulsions, water-in-oil emulsions, the
air–lipid interface of bulk oils and solid fats, and the water–lipid interface of biological
membranes. Oxidation is prevalent at these interfaces as a result of increased
contact with oxygen, the presence of aqueous phase free radicals, the presence of
reactive oxygen generating systems and prooxidative metals, and possibly the migration
of the more polar lipid peroxides out of the hydrophobic lipid core toward
the more polar interface.
The effectiveness of phenolic antioxidants is often dependent on their polarity.
Porter [93] used the term ‘‘antioxidant paradox’’ to describe how polar antioxidants
are most effective in bulk lipids while nonpolar antioxidants are most effective in
dispersed lipids. In bulk tocopherol-stripped corn oil, Trolox (a water-soluble analog
of �-tocopherol) more effectively inhibited lipid peroxide formation than �-tocopherol.
However, when tocopherol-stripped corn oil was emulsified with Tween 20, �tocopherol
inhibited peroxide formation more effectively than Trolox. The observed
increase in activity of �-tocopherol compared to Trolox in emulsified oil was attributed
to its retention in the oil and possibly to its ability (due to its surface activity)
to concentrate at the oil–water interface. The lower activity of Trolox in emulsions
was due to its partitioning into the water phase, where it was not able to inhibit
autoxidation of the corn oil [94]. Similar effects have been observed for the phenolic
antioxidants in rosemary extracts, with the more polar compounds (carnosic and
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