Effects of processing and storage on antioxidant efficacy in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 376

15.5.2 Changes in oil emulsions
In bulk fats, antioxidants and emulsifiers are distributed by chance (Fig.
15.12(c)). In water-in-oil emulsion, emusifiers are oriented with their hydro-
carbon chains in oil, and with their polar groups in the water phase. Nonpolar
antioxidants remain in the oil phase, being not affected by the nonpolar end of
emulsifer molecules (Fig. 15.12(a)). On the contrary, the structure is inversed in
oil-in-water emulsions. Polar groups of emulsifiers are oriented to continuous
water phase and hydrocarbon, nonpolar chains towards oil droplets. Nonpolar
antioxidants remain in the oil phase (Fig. 15.12(b)).
In deep coloured fruit juices (elderberry, blackberry, sour cherry) processed
by conventional technology, about 30±50% anthocyanins, phenols, chlorogenic
acid and cyanidin-3-glucosides were partially lost, too. They were lost without
particular discolouration. Antioxidants were lost in all juices, but to a different
degree (Dietrich et al., 2003).
An emulsion of linoleic acid with Fe(III) salts and ascorbic acid as catalysts
was stored at 30 ëC. Phenolic antioxidants could not prevent the formation of
primary hydroperoxides, but stopped the propagation reaction with free lipidic
radicals. BHA, BHT, -tocopherol and isoeugenol acted as strong antioxidants,
but rosmarinic and caffeic acids were only weak antioxidants in this model
system. Linoleic acid emulsion was stabilized with caseins and whey proteins.
The oxidation of linoleic acid was lower in proteins in the continuous phase by
binding trace metals and increasing the free radical scavenging activity, e.g. by
reacting with bound cysteine or cystine (Ries et al., 2010).
Ascorbic acid and -carotene acted as synergists of casein in hydrolyzate in
model systems (Bzducha and Wolosiak, 2006). The antioxidant activity in
emulsions depends on the composition of emulsifiers. Sodium caseinate and
lactose emulsions were more stable against oxidation than Tween-20 emulsions,
stabilized by antioxidants of low polarity ± -tocopherol and dodecylgallate. In
comparison, the protection by polar antioxidants ± Trolox and gallic acid ± was
less effective (Velasco et al., 2004). Meat was smoked for up to 23 h with
Fig. 15.12 Distribution of a hydrophobic antioxidant in emulsions: (a) water-in-oil
emulsion, (b) oil-in-water emulsion, (c) bulk oil.