Page 292 - Natural Antioxidants, Applications in Foods of Animal Origin

Application of Natural Antioxidants in Dairy Foods 271
VetBooks.ir As mentioned earlier, light also influences milk flavor due to riboflavin-

sensitized effects on milk proteins via oxidation of methionine to methional
(3-methylthiopropionaldehyde) (Patton, 1954; Tada et al., 1971; Sattar et
al., 1977) and also oxidation of other amino acids in the presence of light
and riboflavin. Allen and Parks (1975) reported that exposure of milk serum
to fluorescent light chemically modified 10 amino acids in immunoglobu-
lins. Dimick (1976) reported the considerable loss (~80%) in the activity of
milk lipase due to riboflavin-photosensitized oxidation when the milk was
exposed to sunlight for 30 min. Light- and riboflavin-induced changes in
cheese have also been reported (Deger & Ashoor, 1987).

7.4 QUALITY AND SAFETY ISSUES OF OXIDATION

The secondary oxidation products of lipid oxidation especially α,
β-unsaturated aldehydes, such as 4-hydroxynonenal (4-NHE) or trans-4-
hydroxy-2-hexanal (HHE) are reported to be toxic and very reactive. These
can easily react to proteins or peptides. The interactions between sugar/
lipid oxidation/degradation products and protein often result in addition
of carbonyl groups to protein via covalent binding between the advanced
glycation end products (AGEs), carboxymethyllysine was first AGE to be
identified in milk by Tauer et al. (1999) or advanced lipid oxidation end
products (ALE). There are evidences of the role of these interactions on the
pathologies of several diseases (Baron, 2013).

7.5 METHODS OF MEASUREMENT OF OXIDATION

The methods of detection and measurement of the extent of oxidation,
pertaining to the oxidation of lipid, in the dairy foods are mainly associ-
ated with the measurement of hydroperoxides which is one of the classical
methods for quantifying the lipid oxidation. A number of methods are based
on iodometric titration, that is, hydroperoxides oxidize and liberate iodine
from potassium iodide, the test commonly referred to as peroxide value
determination or spectrophotometric methods, that is, hydroperoxides
oxidize the ferrous to ferric iron in the presence of ammonium thiocyanate
to produce ferric thiocyanate, which can be spectrophotometrically quanti-
fied at 505 nm (Loftus Hills & Thiel, 1946), also hydroperoxides of the
oxidized fat reacts with 1,5-diphenyl-carbohydrazide to yield red-colored
products (Hamm et al., 1965). The progress of auto-oxidation is measured