Food Lipids: Chemistry, Nutrition, and Biotechnology

A. Synthetic Antioxidants
Synthetic antioxidants are intentionally added to foods to inhibit lipid oxidation.
Synthetic antioxidants approved for use in food include BHA, BHT, PG (also octyl
and dodecyl gallate), ethoxyquin, ascorbyl palmitate, and TBHQ. The synthesis of
novel antioxidants for food use is limited by rising costs of research and development,
costs associated with safety assessment, and the time required to obtain regulatory
approval of additives [17]. These restrictions, as well as growing consumer
preference for natural food additives, has led industry to emphasize natural materials
as a source of novel antioxidants.
Phenolic compounds represent some of the oldest and most frequently used
antioxidants in foods. The differences in antioxidant activity of the phenolic antioxidants
are due to variations in structure that directly influence physical properties.
Phenols in which the aromatic ring contains alkyl groups (hindered phenols) are
extremely effective antioxidants. Hindered phenols are also effective antimicrobials
in foods. A good product’s characteristics ultimately determine the selection of the
phenolic antioxidant. BHA and BHT are fairly heat stable and are used in heatprocessed
foods. PG decomposes at 148�C and is inappropriate for high temperature
processing. Therefore, heat-stable TBHQ is useful in frying applications. BHA and
BHT are strongly lipophilic and are used extensively in oil-in-water emulsions. BHA
and BHT are also typically used together in mixtures, acting synergistically. A summary
of the physical properties and applications of phenolic antioxidants is provided
in Table 1.
Titles 9 and 21 of the U.S. Code of Federal Regulations (CFR) govern the use
of antioxidants in meat and poultry products and in foods, respectively. Phenolic
antioxidants are effective at low concentration and are often used at levels less than
0.01% [6]. The level of phenolic antioxidants permitted in the United States varies
according to the product. As specified in 21 CFR, 172.110 and 172.115, limitations
for BHA and BHT alone or in combination are as follows for specific products:
potato granules, 10 ppm; dehydrated potato shreds, dry breakfast cereals, potato
flakes, sweet potato flakes, 50 ppm; and emulsion stabilizers for shortenings, 200
ppm. At high levels, phenolic compounds become prooxidants because of their high
reactivity and participation in the initiation process. Allowable limits vary greatly
depending on the food product and the antioxidant. Regulations concerning synthetic
antioxidants vary greatly from country to country and complicate marketing of products
internationally.
Commercial antioxidant preparations are available in solid and liquid blends.
Liquid blends are convenient because the antioxidant is solubilized for each addition
during processing. Solvents include vegetable oils, propylene glycol, glyceryl monooleate,
ethanol, and acetylated monoglycerides [5]. Antioxidant preparations typically
contain mixtures of phenolic antioxidants, a synergist, and a solvent system. Some
of the most important synthetic antioxidants are discussed in the following sections.
Structures are provided in Figure 2.
1. Butylated Hydroxyanisole
BHA is typically used as a 9:1 mixture of 3-BHA and 2-BHA isomers [6]. The 3isomer
shows higher antioxidant activity than the 2-isomer [5]. It is a waxy, monophenolic,
white solid that is fat-soluble. It is effective at preventing oxidation of
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