Page 378 - Natural Antioxidants, Applications in Foods of Animal Origin

Control of Lipid Oxidation in Muscle Food 357
VetBooks.ir Quercetin (2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one)

is the most abundant flavonoid in foods, and due to its antioxidant activity
and other beneficial properties has been object of special attention in the past
years (Alrawaiq & Abdullah, 2014). Although it has not been confirmed scien-
tifically as a specific therapeutic nor approved by any regulatory agency, it is
widely used as food supplement in the treatment of several health problems.
The Joint FAO/WHO Expert Committee on Food Additives evaluated quer-
cetin for use in food in 1977 (Harwood et al., 2007), but limited data on its
toxicity were available at the time of the evaluation which precluded the estab-
lishing an acceptable daily intake (ADI). In Japan, quercetin is permitted as
a food additive since the 1996 year (Harwood et al., 2007). Other flavonoids
such as myricetin or robinetin have a recognized high antioxidant activity. All
those compounds could be in the future efficient food antioxidant additives
after approval by the health authorities, upon proof of their harmlessness.
Phenolic acids are substances containing a phenolic ring and a carbox-
ylic function, therefore having a C6-C1 skeleton. They can be mono-, di- or
tri-hydroxybenzoic acids depending on the number of positions hydroxyl-
ated in the phenolic ring. The antioxidant activity of the phenolic acids and
their corresponding esters is determined by the number of hydroxyl groups.
Some concrete phenolic acids such as cafeic, coumaric, ferulic, gallic, and
protocatechuic acid are known as molecules possessing a not negligible
antioxidant activity. They could be in the future successfully used for this
purpose in foods after further studies on their stability and safety.

9.3.1.2 ASCORBIC ACID

Ascorbic acid (C H O ) ((5R)-[(1S)-1,2-Dihydroxyethyl]-3,4-dihydroxy-
8
6
6
furan-2(5h)-one) is a molecule with antioxidant and vitamin (vitamin C)
activities widely present in vegetables and fruits, and to a lesser extent in
animal tissues. It is oxidized with successive loss of two electrons to form
dehydroascorbic acid. It reacts with oxidants (reactive oxygen species),
such as the hydroxyl radical. Therefore, ascorbate can terminate these chain
radical reactions by electron transfer. Ascorbic acid is special because it can
transfer a single electron, due to the resonance-stabilized nature of its own
radical ion.
Ascorbic acid is an active antioxidant in aqueous media, because of its
water-soluble character, but only at high concentrations (around 10 mol/L).
−3
A pro-oxidant activity is observed at lower concentrations (10 mol/L),
−5
especially at high oxygen tensions and when heavy metal ions are present.