Page 68 - Natural Antioxidants, Applications in Foods of Animal Origin

Natural Antioxidants: Occurrence and Their Role in Food Preservation 47
VetBooks.ir the strong antiradical action. On the other hand, four postulates have been

proposed to explain the antioxidant activity of PL:

i) synergism between PL and tocopherols;
ii) chelation of pro-oxidant metals by phosphate groups;
iii) formation of Maillard-type products between PL and oxidation prod-
ucts; and
iv) action as an oxygen barrier between oil/air interfaces (Ramadan,
2012).

2.6 ROLE OF FATTY ACIDS IN OXIDATIVE STABILITY

All edible oils and fats consist of triglycerides with a variety of fatty acids
that differ in chain-length (number of carbon atoms in molecule), degree
of saturation (number of double bond in carbon chain), position of double
bond within the carbon chain, and geometry of each double bond (cis and
trans isomers). Oleic acid is the most abundant monounsaturated fatty acid
(MUFA) in all the common edible oils (Gunstone, 2000; Abdulkarim et al.,
2007). Compared with polyunsaturated fatty acids (PUFA), oleic acid is
more stable toward oxidation both at ambient storage temperatures and at the
high temperatures that prevail during the cooking and frying of food. There-
fore, oils with high amounts of oleic acid are slower to develop oxidative
rancidity during shelf life or undergo oxidative decomposition during frying
than those oils that contain high amounts of PUFA. The various strengths
of hydrogen–carbon bond of fatty acids explain the differences of oxidation
rates of stearic, oleic, linoleic, and linoleic acids during thermal oxidation
or autoxidation. Compared with (PUFA) (ω-6 and ω-3 PUFA), oleic acid
(ω-9 MUFA) and saturated fatty acids are more stable toward oxidation both
at ambient storage temperatures and at the high temperatures that prevail
during the cooking and frying of food (Abdulkarim et al., 2007).
The oil rich in linoleic acid is more easily polymerized during deep-fat
frying than the oil rich in oleic acid. The energy required to break carbon–
hydrogen bond on the carbon 11 of linoleic acid is 50 kcal/mol (Min & Boff,
2002; Choe & Min, 2007). The double bonds at carbon 9 and carbon 12
decrease the carbon–hydrogen bond at carbon 11 by withdrawing electrons.
The carbon–hydrogen bond on carbon 8 or 11, which is α to the double
bond of oleic acid, is about 75 kcal/mol. The carbon–hydrogen bond on the
saturated carbon without any double bond next to it is ~100 kcal/mol (Min
& Boff, 2002; Choe & Min, 2007). Oxidation produces hydroperoxides and