Page 287 - Natural Antioxidants, Applications in Foods of Animal Origin

266 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir TABLE 7.1 Oxidants and Antioxidants in Milk.

Oxidants Antioxidants Both (oxidants and
antioxidants)
Polyunsaturated fatty acids of Casein Phospholipids
triglycerides, phospholipids,
cholesterol esters
Riboflavin Lactoferrin Thiol group
Proteins α- tocopherol
Transition metal ions- cupric, ferric Carotenoids (β-carotene)
Haem proteins Maltol (in heated milk)
Ferri-porphyrin
Copper-protein complex with
phospholipids
Xanthine oxidoreductase
Sulfhydryl oxidase

Milk also contains appreciable amount of antioxidants. Vitamins
including α-tocopherol, principal tocopherol of the eight vitamers of the
vitamin E, act as a free radical scavenger. The concentration of α-tocopherol
in cow’s milk ranges from 3.0 to 5.0 mg/L (Hendricks & Guo, 2006).
1
α-tocopherol is also reported to quench singlet oxygen ( O ) via a charge-
2
transfer scavenging mechanism (Yamauchi & Matsushita, 1977; Burton
& Ingold, 1981). Vitamin A and carotenoids act as antioxidant due to the
hydrophobic chain of polyene units that quench O , neutralize thiyl radi-
1
2
cals and combine with peroxyl radicals and stabilize the same (Palace et
al., 1999). Beta-carotene also acts as antioxidant in milk. It is reported to
offer good protection against light-induced lipid oxidation and it inhibits
the chlorophyll-sensitized photo-oxidation of methyl linoleate (Terao et al.,
1980). In addition, it provides protection against riboflavin degradation by
competing for absorption of light. However, this protective effect disappears
outside the absorption band of carotene (i.e., <366 nm) as the protective
mechanism is not a quenching effect of radical or O , but absorption (filter)
1
2
effect of the incident light (Hansen & Skibsted, 2000). Some of the indig-
enous enzymes of milk also act as antioxidants, while others may play a role
in promoting the lipid oxidation like Xanthine oxidoreductase. Sulfhydryl
oxidase is proposed to cause oxidation of thiols in ultra-high temperature
(UHT) milk, in conjunction with lactoperoxidase (to destroy the resultant