Antioxidants Compounds that prevent

As we will learn in Section 15.12, many antioxidants-compounds that prevent unwanted radical oxidation reactions from occurring—are phenols, compounds that contain an CH group bonded directly to a benzene ring. 

Vitamin E (a-tocopherol) (fig. 10.26) was recognized in 1926 as an organic-soluble compound that prevented sterility in rats. The function of this vitamin still has not been clearly established. A favorite theory is that it is an antioxidant that prevents peroxidation of polyunsaturated fatty acids. Tocopherol certainly prevents peroxidation in vitro, and it can be replaced by other antioxidants. However, other antioxidants do not relieve all the symptoms of vitamin E deficiency. 

Antioxidants Compounds that are easily oxidized can act as antioxidants to prevent other compounds from being oxidized. Vitamins C and E protect living cells from oxidative damage by acting as antioxidants. Why does adding lemon juice to fruit salad prevent browning of the fruit ... 

Butylated hydroxyanisole (BYOO-til-ay-ted hi-DROK-see-ANN-i-sole) and butylated hydroxytoluene (BYOO-til-ay-ted hi-DROK-see-TOL-yoo-een) are very popular food additives used to preserve fats and oils. They both are antioxidants, which are compounds that prevent oxygen from reacting with substances and changing them into other materials. BHA and BHT prevent the oxidation of fats and oils that would convert them into rancid, foul-smelling, harmful products. 

A preservative is a substance that prevents or inhibits microbial growth and extends the shelf life of the drug products. In most pharmaceutical drug products, only a few compounds are typically selected as preservatives. For efficiency, a generic method should be developed for the types of preservatives that are more commonly used. For example, butylated hydroxytoluene (BHT) is an antioxidant commonly used in many solid dosage formulations to retard oxidative degradation of the excipients. 

Antioxidants These are naturally occurring compounds that have the ability to lower the levels of free radicals they include vitamins C and E, the carotenoids and the flavonoids. Vitamin E and the carotenoids are particularly important in preventing oxidation of the unsaturated fatty acids within the LDL particle and within membranes of cells. 

Carotenoids are isoprenoid compounds that are biosynthesized only by plants and microorganisms. Some carotenoids (a- and p-carotene, p-cryptoxanthine) can be cleaved into vitamin A (retinol) by an enzyme in the small intestine. Carotenoids have been reported to present some effects in the prevention of cardiovascular diseases [410] and in the prevention of some kind of cancers [411]. Furthermore, antioxidant activity has been widely reported [411-414] but a switch to pro-oxidant activity can occur as a function of oxygen concentration [415,416]. 

Oxidation results from the interactions between atmospheric oxygen and the double bonds of unsaturated fatty acids. Several parameters can catalyze lipid oxidation, while others can prevent or slow down the reactions. Metals, light, moisture and heat can all enhance oxidation, while antioxidant compounds (e.g., BHT and vitamin E) can be utilized to retard oxidation. Oxidation of double bonds leads to intermediate peroxides that eventually break down into a variety of stable compounds. 

Compounds that can scavenge radicals are also referred to as antioxidants. The best known anti-oxidants are vitamin C and vitamin E. Vitamin C is L-ascorbate (7.8), a good reducing agent that prevents oxidation of other molecules. The oxidized form of L-ascorbate is L-dehydroascorbic acid (7.9). Vitamin E is a mixture of a-, [3-, y-, and 8-tocopherol (7.10a-d). Of these four compounds, a-tocopherol is the most effective. Vitamin E is lipid-soluble and has the ability to disrupt the chain reaction during lipid peroxidation (see Chapter 2, Section 1.9). 

Use of plant parts (bark, leaves, seeds, etc.) and their extracts to preserve food from developing a rancid taste is a practice that has continued since prehistoric time. There is evidence that even for the industrial materials, plant-based components were used as antidrying agents to prevent oxidation and polymerization of polyunsaturated fatty acid-rich plant oils (2, 5, 48). During the past two decades, intensive research has been carried out on naturally occurring antioxidative compounds from different sources. The main drive behind this search was to reduce the use of synthetic compounds as food additives because of their potential negative health effects and as a result of consumer demand. 

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