Natural antioxidants as food and beverage ingredients - Natural Food Additives, Ingredients and Flavourings - page 99

antioxidant options: their chemical structures, mechanisms of action, sources,
applications where they work best, and those where they do not.

5.2 Natural antioxidants: background
Oxidation can be a main issue in foods and a major factor in shortening shelf life
by generating off-fl avors in lipid containing foods. Oxidation can also lead to loss
of color through oxidative degradation of pigments, as well as loss of nutrients
and vitamins. It can even change the texture and the functionality by impacting
protein structure. Therefore, oxidation affects a wide array of foods such as meats,
oils, fried foods, dressings, dairy products, baked goods and extruded snacks.
Using antioxidants constitute a major oxidation defense strategy.

5.2.1 Historic synopsis
Natural preservation techniques such as smoking meat and using spices have been
used since ancient times, but without necessarily understanding the underlying
chemical nature of the process on the molecular level. The era between the 1920s
and 1950s witnessed the start of using antioxidants as individual food additives.
Gum guaiac was the fi rst antioxidant for the stabilization of lard in the 1930s
(Grettie 1933), followed by lecithin and tocopherols (Higgins and Black 1944).
The middle of the twentieth century witnessed remarkable advancements in the
area of synthetic chemicals - including the development of inexpensive synthetic
antioxidants. While many of the synthetic antioxidants are not suitable for use in
foods, a few of the compounds developed originally for the plastics industry, such
as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), became
commonly used in the food industry. Another shift in preference happened in the
middle to latter part of the twentieth century: consumers became more suspicious
of the use of synthetic chemicals. In turn, this spurred efforts to better understand
and utilize antioxidant substances found in nature and re-visit the antioxidative
effects from spices and other natural resources.

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5.2.2 Lipid oxidation mechanisms
Lipid oxidation is a free radical reaction comprising three phases: initiation,
propagation and termination (Fig. 5.1) (Berdahl et al. 2010):
• Initiation phase: In this initial stage, free radicals are generated by hydrogen
abstraction reactions mediated by metal ions, light, radiation or other promoting
factors. The Fenton reaction is often the start, converting hydrogen peroxide
and iron(II) into hydroxide ions, iron(III) and hydroxyl radicals, with the latter
able to abstract a hydrogen from a lipid.
• Propagation stage: The key intermediate formed is a highly reactive carbon-
centered lipid free radical which reacts rapidly with molecular oxygen, at near
diffusion-controlled limits, generating hydroperoxyl radicals. In turn, these