Page 288 - Natural Antioxidants, Applications in Foods of Animal Origin

Application of Natural Antioxidants in Dairy Foods 267
VetBooks.ir H O ) by doing away with the pro-oxidants resulting from auto-oxidation of

2
2
thiols (Swaisgood & Abraham, 1980).
The products and by-products obtained from processing of milk can also
serve as potent antioxidant. Steps associated with preparation of cream and
during pre-heating of milk for milk powder manufacture, the antioxida-
tive activity gets increased due to enhanced activation of free sulfhydryl
groups (Farkye, 2006; Keogh, 2006). It is proposed that buttermilk solids are
effective in reducing the severity of lipid oxidation during chain propaga-
tion stage; however, it is ineffective in delaying the onset of lipid oxidation.
Thus, incorporation of buttermilk solids into the food matrices can be an
approach to stabilize against lipid peroxidation (Wong & Kitts, 2003). The
antioxidant activity of buttermilk may be attributed to the presence of sulf-
hydryl content. Few of the workers (Dugan, 1980; Eichner, 1980; Eriksson,
1982) reported that carbonyl-amine reactions between lactose and milk
proteins produce intermediates having potent antioxidative activity and may
play role in stabilization of milk fat (Wyatt & Day, 1965). Maltol, an impor-
tant flavor component in the heated milk also exhibit powerful antioxidant
activity (O’Brien, 2009). However, it is also reported that browning reac-
tion products may exert anti-nutritional and toxicological effects (O’Brien
& Morrissey, 1989). Thus, a balance between pro-oxidant and antioxidant
factors is critical for the oxidative stability of milk (Stapelfeldt et al., 1999;
Morales et al., 2000).

7.3 OXIDATION IN DAIRY PRODUCTS

Oxidation of dairy products involves the addition of oxygen atom to or the
abstraction of hydrogen atom from the different chemical moieties present
in the milk, which is further associated with conversion of primary hydroxyl
groups (alcohols) to aldehyde and finally to carboxylic acid functionality by
either chemically or biochemically mediated oxidation. In few instances, the
oxidation reaction is desirable and may lead to an improvement in the product
quality, such as oxidative cross-linking of proteins to manipulate viscosity
and gelation in dairy products. However, in majority of the cases, food oxida-
tion leads to decrease in consumer acceptance, minimizes the shelf life of the
product and in few may even be associated with formation of anti-nutrients
and toxicity as well. The two principal types of oxidation that contribute to
food deterioration are autoxidation of unsaturated fatty acids and enzyme-
catalyzed reaction. The residues susceptible for oxidation are also present on
proteins and carbohydrates, besides being present on lipids. Radicals formed