Antioxidants as Food Additives

An antioxidant, in the context of food chemistry, is a substance that delays the onset of oxidation or slows its rate once it has begun, and food manufacturers use antioxidants specifically to extend a packaged food's shelf life. Chemically, antioxidants work by reacting with the oxygen-containing free radicals that would otherwise attack the food, intercepting them before they can trigger the oxidative rancidity described earlier in this section. Vitamin E (tocopherol) is the chapter's example of a natural antioxidant, and it is added directly to packaged edible oils for this purpose. Structurally, tocopherol is a chromanol (benzopyran) ring system carrying a phenolic -OH group and several methyl substituents, fused to a long saturated hydrocarbon side chain. The two structural features map directly onto its two functional roles: the phenolic -OH group on the ring is what gives tocopherol its actual antioxidant activity (donating a hydrogen atom to quench a free radical), while the long saturated hydrocarbon chain is what makes the whole molecule fat-soluble, allowing it to dissolve into and remain within an oil. Vitamin E occurs naturally in foods such as wheat germ, nuts, seeds, green leafy vegetables, and oils like safflower oil. For economic reasons, packaged foods more often use synthetic antioxidants as additives instead of natural vitamin E, and the chapter notes that the structural units common to synthetic antioxidants are a phenolic -OH group together with a tertiary-butyl group. Its worked example is BHT (3,5-di-tert-butyl-4-hydroxytoluene): a toluene …