Tocopherols as Food Antioxidants
Consumer satisfaction is a top priority of all food processors. Meeting consumer demands for fresh, wholesome foods may depend on the processor's ability to control, through innovation, the many factors that can affect the quality of foods from the time of processing until they are eaten. The processor must try to eliminate, or at least minimize, the effects of inherent problems such as microbial spoilage, staling, enzymatic changes, and oxidation. Technologies developed in recent years along with the skillful use of approved additives and processing aids have lessened the burden of overcoming many of these problerns, but obtaining adequate shelf life is still a major concern of many food processors.
Oxidative rancidity is often responsible for the off-odors and off-flavors that can develop in many foods. Rancid foods are characterized by sharp offensive odors and tastes and may be actually unfit for consumption. The condition of rancidity develops in foods that contain fats or oils and occurs when atmospheric (molecular) oxygen reacts with the unsaturated part of fatty acid esters to form peroxides, hydroperoxides, and finally carbonyl compounds. Reaction products such as aldehydes, acids, ketones, and alcohols impart the harsh flavors and odors that render foods useless.
There are some important facts about oxidative degradation of foods that need to be remembered.
2. Once the oxidative reaction is initiated and left unchecked, it will progress at an ever inereasing rate.
3. Most important, once a food item becomes rancid, nothing can reverse the oxidative process or restore the food to its original quality.
For many years, antioxidants have been used safely and effectively to retard oxidative deterioration of foods.
Antioxidants are compounds or substances that will inhibit or interfere with the formation of free radicals in food fats, thus terminating the oxidative reaction in its initiating step. From a practical standpoint, this simply means that an antioxidant system properly selected to meet the needs of a particular food item and correctly applied will help to maintain the product's original freshness, flavor, and odor for a longer period of time than would otherwise be possible.
Antioxidants are generally classified as either synthetic or natural products, and the number of compounds approved for food use in the United States and most foreign countries is quite limited, Four synthetic products, tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl gallate (PG), are the ones most widely used and fill most of the needs for food antioxidants (1). In the United States, they are legal under the food additive regulations at concentrations of not over 200 ppm of the fat content (including essential oil content) of food products. Certain mixtures are permitted, and for certain low fat foods, specific concentrations based on the food itself rather than its fat content are permitted. The sections of the U.S. Code of Federal Regulations enforced by the U.S. Food and Drug Administration (FDA) governing the use of antioxidants are 21 CFR 182.3169 for BHA; 21 CFR 182.3173 for BHT; 21 CFR 172.185 for TBHQ; and 21 CFR 184.1660 for PG. Regulations enforced by the U.S. Department of Agriculture (USDA) for the use of these antioxidants in meat products are at 9 CFR 318.7.
Natural Source Products
The list of naturally occurring antioxidants includes tocopherols, lecithin, rosemary extract, gum guaiac, ascorbic acid, and a few others. Tocopherols enjoy the greatest popularity of the natural source products. They occur naturally in vegetable oils, the prime commercial source being soybeans. They are extracted from tocopherol-rich deodorizer distillates which are byproducts from steam stripping of vegetable oils during their final processing step.
Alpha-Tocopherol is primarily recognized as a source of vitamin E and is available as a natural product (d-alphatocopherol) or a synthetic product (dl-alpha-tocopherol). Alpha-tocopherols exhibit some antioxidant potency, but the gamma- and delta-tocopherol epimers are considered to be substantially more effective antioxidants (Figure 1). For this reason, the products that are most appropriate for use as antioxidants usually contain gamma- and delta-Tocopherols at a minimum of 80% of the total tocopherol concentration. These mixed tocopherol concentrates are proving to be valuable ingredients where regulations do not permit the use of more effective synthetic antioxidants or where natural source antioxidants are simply preferred. A comparison of the effectiveness of alpha-tocopherols versus mixed tocopherols is shown in Table I, based on data from our laboratory tests (2).
Tocopherols are readily soluble in fats and oils. They may be applied to food items by using the techniques applicable to other food grade antioxidants. One fundamental rule should be followed in their application and that is to ensure thorough dispersion of the tocopherols into the fat or oil portion of the food product.
Tocopherols used at relatively low concentrations (100 to 300 ppm of fat weight) are effective antioxidants in a wide variety of food products. Their effectiveness is known to diminish when used at high levels (>500 ppm of fat weight). Oils and foods from vegetable origins generally contain generous levels of tocopherols, Even processed vegetable oils contain residual amounts (500-700 ppm). As a result, the benefits obtained from the application of additional tocopherols to these products are only marginal. Products from sources that are low or deficient in natural antioxidants respond quite well to the application of tocopherols. Food fats such as lard, tallow, and butter oils are good examples. The data from our laboratory in Table II demonstrate the effectiveness of tocopherols for improving the oxidative stability of these fats (2). Tocopherols are also applicable to poultry fats, paraffin wax, and fish oils.
Important food ingredients such as essential oils and flavorings are susceptible to oxidative changes that affect odor, navor, and color. Tocopherols are very effective for preventing deterioration of these ingredients. The effect on citrus oils is shown in Table III (2).
It is well documented that tocopherols effectively improve the stability of many food fats and oils. One consideration still remains, and that is the effect that processing conditions might have on the antioxidant. Some antioxidants can be destroyed by heat. Others might be gradually lost through volatilization or steam distillation. Failure of an antioxidant to carry through the process of cooking will result in food products with poor shelf life. Tocopherols are heat stable and are not volatile or steam distillable under normal conditions of cooking. The data in Table IV illustrate this carry-through effectiveness of tocopherols in deep-fried and baked foods (2).
Natural source tocopherols are regulated in the United States by FDA principally at 21 CFR 182.3890 and by USDA at 9 CFR 318.7. In 1978 FDA proposed to affirm GRAS status for mixed concentrated tocopherols under 21 CFR 184.1894, although no specific follow-up action took place. Many foreign countries permit the use of tocopherols in foods. These include Canada, Japan, Korea, Australia, and all countries of the European Economic Community. Food processors must determine that their use of tocopherols as antioxidants is lawful in their intended applications.
1. Sherwin, E.R. Antioxidants for Food Fats and
Oils. J. Am. Oil Chem. Soc. 49:468, 1972.