Page 66 - Natural Antioxidants, Applications in Foods of Animal Origin

Natural Antioxidants: Occurrence and Their Role in Food Preservation 45
VetBooks.ir have expressed concern about the safety of preservatives and additives in

their food (Brewer et al., 1994; Brewer & Prestat, 2002; Rojas & Brewer,
2008; Brewer, 2011). Sloan (1999) reported that one of the top 10 trends for
the food industry to watch included the sales of natural, organic, and vege-
tarian foods. There is a clear trend in consumer preference for clean labeling
(Hillmann, 2010; Brewer, 2011), for food ingredients and additives that are
organic/natural with names that are familiar, and that are perceived to be
healthy (Joppen, 2006; Brewer, 2011). In addition, the call for sustainable
sources and environment friendly production is forcing the food industry to
move in that direction (Berger, 2009; Brewer, 2011). Phenolic antioxidants
can inhibit free radical formation and/or interrupt propagation of autoxida-
tion. Fat-soluble vitamin E (α-tocopherol (α-T)) and water-soluble vitamin
C (L-ascorbic acid (AH )) are both effective in the appropriate matrix. Plant
2
extracts, generally used for their flavoring characteristics, often have strong
H-donating activity thus making them extremely effective antioxidants
(Brewer, 2011).

2.4 NATURAL ANTIOXIDANTS: DYNAMICS AND MECHANISM

Chain-breaking antioxidants differ in their antioxidative effectiveness
depending on their chemical characteristics and physical location within a
food (proximity to membrane phospholipids (PL), emulsion interfaces, or in
the aqueous phase). The chemical potency of an antioxidant and solubility
in oil influence its accessibility to peroxy radicals especially in membrane,
micellar and emulsion systems, and the amphiphilic character required for
effectiveness in these systems (Wanatabe et al., 2010; Brewer, 2011). Anti-
oxidant effectiveness is related to activation energy, rate constants, oxida-
tion–reduction potential, ease with which the antioxidant is lost or destroyed
(volatility and heat susceptibility), and antioxidant solubility (Nawar, 1996;
Brewer, 2011). In addition, inhibitor and chain propagation reactions are both
exothermic. As the A:H and R:H bond dissociation energies increase, the
activation increases and the antioxidant efficiency decreases. Conversely, as
these bond energies decrease, the antioxidant efficiency increases. The most
effective antioxidants are those that interrupt the free radical chain reaction.
Usually containing aromatic or phenolic rings, these antioxidants donate H
to the free radicals formed during oxidation becoming a radical themselves.
These radical intermediates are stabilized by the resonance delocalization
of the electron within the aromatic ring and formation of quinone struc-
tures (Nawar, 1996; Brewer, 2011). In addition, many of the phenolics lack