Effects of processing and storage on antioxidant efficacy in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 370

contribute to the total antioxidant functionality. Polymers could dimerize during
slow oxidation, which explains the free radical scavenging activity of
polyphenols (Hotta et al., 2002).
If oxidized lipid free radicals do not react with antioxidants, the lipid
hydroperoxides decompose with formation of both nonvolatile and volatile
products, mostly aldehydes, the flavour of which is unpleasant for human
consumers in most cases. Formation of objectionable volatile oxidation products
was inhibited by antioxidants ± TBHQ, thiodipropionic acid, and thiourea, the
first mentioned being the most powerful one (Kajimoto and Murakami, 1998).
Minced jack mackerel was stored at ÿ20 ëC with addition of polar inhibitors,
and the best stability and sensorial properties were obtained with erythrosorbate
(an isomer of ascorbic acid), and with sodium phosphate and their mixtures.
Sodium polyphosphate and its mixtures with some synthetic antioxidants were
also active (Maldonaldo et al., 2006). Their activity resides in their metal
complexing capacity.
Substituted phenolic compounds may contain another active group. An
example of caffeic acid is given in Fig. 15.7. Free radicals formed from caffeic
acid easily polymerize with formation of a dimer, again possessing the anti-
oxidant activity. Caffeic acid reacted with cysteine forming 2,5-cysteinylcaffeic
acid, which has higher antioxidant activity than caffeic acid (Bassil et al., 2005).
Quinones formed by oxidation of antioxidants can react with free amine
groups of proteins (bound lysine ± Fig. 15.8) or phospholipids (phosphatidyl-
ethanolamine or phosphatidylcholine) with formation of an imine (Fig. 15.9) ± a
very reactive derivative. A simplified review of antioxidant reactions was
published earlier (Pokorn , 2006).
Green tea antioxidants contain (ÿ)-epigallocatechin gallate and (ÿ)-epigallo-
catechin as the most active components (Fig. 15.10). The triphenyl-B-ring is the
Fig. 15.7 Dimerization of caffeic acid: (a) Caffeic acid, (b) tricyclic dimer.
Fig. 15.8 Reaction of amine with para-quinone: (a) primary amine,
(b) para-quinimine.