Synthetic and natural antioxidant additives in food stabilization: current applications and future research - Oxidation in Foods and Beverages and Antioxidant Applications - page 297

Fig. 12.18 Chemical structure of -carotene.
and vegetables whose orange, yellow or red coloration stems from their
extensively conjugated double bond systems. A main interest in the use of
carotenoids ± besides being natural food colorants ± is due to possible connec-
tions between consumption and health. The health effects are thought to be
associated with their antioxidant properties. Epidemiological studies have
suggested a relationship between the ingestion of carotenoids and good health
(Paiva and Russel, 1999).
The extended electron delocalization in carotenoids is the driving force
behind the radical scavenging ability of these natural antioxidants. Rajalakshmi
and Narasimhan (1996) suggest that carotenoids act as singlet oxygen quenchers
and hydrogen peroxide scavengers at high oxygen pressure, and chain-breaking
primary antioxidants at low oxygen pressure when singlet oxygen is not present.
-Carotene (Fig. 12.18) contributes to the oxidative stability of food systems
where they are naturally present, such as palm oil (500±3000 ppm) and carrots
(Thyrion, 1999). Carotenoids contribute to the oxidative stability of foods when
they are used as additives, including, water-in-oil emulsions and margarines
(Pokorn et al., 2001), butter, butterfat, coconut oil and corn oil (Nanditha and
Prabhasankar, 2009). Additionally, -carotene exhibited synergistic effects in
oil-in-water emulsions when combined with with other carotenoids, such as
bixin from annatto (Kiokias and Gordon, 2003) and when combined with -
tocopherol (Li et al., 1995).
In spite of their antioxidant benefits in foods, carotenoids are very sensitive to
light and heat and other food properties such as pH and the presence of metal
ions (Thyrion, 1999).
12.5.4 Natural chelators
Most of the previously mentioned natural antioxidants function principally as
primary antioxidants by trapping the generated radicals and eliminating them.
There are only few natural antioxidants that work by sequestering metal ions and
hence are called `preventative antioxidants'.
While it is usually assumed that many plant phenolics with multiple phenolic
groups can act both as radical scavengers and metal chelators, there are some
natural molecules that can stabilize food with metal chelating being their main
mode of action. The most common ones are citric acid, phospholipids and amino
acid/peptides/proteins.