Irradiation of Foods

Irradiation of Foods Supplies the Necessary Vitamin D

Absorption of Rays Fortifies Diet

Ruth C. Clouse, S. M., Explains this Process


                Reference has already been made to the almost simultaneous announcements by Hess and by Steenbock of the successful activation of foods by irradiation with ultraviolet rays. Further work by these investigators and others has shown that many foods may be made powerful antirachitic agents by this means.

Many Products Can be Irradiated

The foods that have been successfully irradiated include a long list: numerous oils and fats—olive, cottonseed, linseed, corn and coconut oils, lard, oleo-margarine and butter; cereal products—refined wheat flour, whole wheat flour, shredded wheat, cream of wheat, oatmeal and even cornstarch; meat; milk, whole or dry; various vegetables, yeast, orange juice, chocolate and ice cream.

By irradiation, the potency of egg yolk has been increased from ten to twenty times and that of butter fat from fourteen to twenty times by irradiation. Sugar is almost the only natural food for which attempted irradiation has been unsuccessful. Liquid petrolatum cannot be activated and neither can rancid oils or fats apparently because the activatable substance is destroyed during the development of rancidity.

Fearing the commercial exploitation of a procedure endowed with such great possibilities for harm, Steenbock, in 1924, patented the process of the irradiation of foods and medicinal by ultraviolet rays. The patent has, however, been assigned to an organization formed for the purpose of receiving it, the Wisconsin Alumni Research Foundation. The foundation sells licenses to manufacturers desiring to use the process, and controls their procedure and even their advertising. Profits from the licenses go to the foundation, not to Steenbock himself. Rights to manufacture under the patent have sold to the Quaker Oats Company, the Fleischmann Yeast Company, the Dry Mild Company, the Sawyer Biscuit Company and also to other companies in the United States, England and Germany.

The process of irradiation is usually carried out by exposing the material in a thin layer on a moving belt which passes under a battery of mercury vapor quartz or carbon arc lamps. Solid material may be allowed to fall once or twice to lower belts to secure a partial turning over of the particles, and liquids, instead of passing over a belt below the light, may be allowed to fall in a thin film around or in front of an ultraviolet generator.

Long exposures, of one hour or more, may develop disagreeable tastes and odors in the food and may also result in an appreciable reduction in the content of other vitamins, especially vitamins A and C. Maximum potency can, however, be developed in very short exposures, with no effect whatever on the flavor or the appearance of the food.

Supple and his associates in the Research Laboratories of the Dry Milk Company report that the length of time required for maximum activation of milk powder depends to some extent on the fat content of the milk but that even skim milk reached its maximum potency in forty-eight seconds. Dry milk samples containing more than 5 percent of butter fat attained a high degree of potency after irradiation for sixteen seconds.

Short periods of irradiation are equally effective for cereals. In a recent article, Steenbock writes “We have found an exposure of a fraction of a second with a battery of quartz mercury vapor lamps entirely satisfactory.”

Longer Time Necessary for Some Foods

For butter, longer periods seem to be necessary. Steenbock and Wirick report that the most favorable conditions for the development of antirachitic potency are thirty minutes’ exposure at a depth of 0.16 cm. The greater part of the antirachitic potency is developed in the first ten minutes, however.

Fortunately the irradiation of foods need not greatly increase their cost. The Quaker Oats Company is selling irradiated cereals at no advance in retail price, and Dorcas of the National Carbon Company in Cleveland writes that the cost of the irradiation of any food “may be expressed by cents, rather than dollars, per ton of food treated.”

Antirachitic Property is Stable Factor

Antirachitic potency developed in foods by irradiation appears to be a stable property. Steenbock reports that irradiated cereals held at temperatures as high as 60 C. for sixteen months showed no decrease in potency. After from twenty-three to twenty-eight months there was some reduction, but long before this time even unirradiated cereals kept under the same conditions had developed a strong odor and taste and were entirely unfit for human consumption.

Irradiated dried milk kept for six months in a cupboard under ordinary conditions lost but little of its potency, and even after a year it had deteriorated only moderately. Irradiated butter fat retained most of its potency during storage for seven months in a refrigerator.

Ordinary processes of cooking also do not have any effect on the potency of irradiated cereals, although the vitamin may be destroyed by commercial baking if the temperature is allowed to go too high.

For the irradiation of milk, perhaps even more than for other foods, especial care must be taken to prevent the development of disagreeable tastes and odors. But if the conditions of the irradiation are properly controlled, a highly satisfactory product may be prepared.

If the irradiation is carries out for but a few seconds, not only is there no change in flavor but the other vitamins of the mild are unaffected. Supple and Dow report a slight destruction of the antiscorbutic vitamin in milk irradiated in liquid form, but, they write, “Comparatively considered, it is probable that the degree of destruction of vitamin C . . . does not reduce the level of this factor bellow that frequently found in nonirradiated, natural fluid milk.” Dry milk irradiated by ultraviolet rays for periods as long as twenty minutes did not show any evidence of the destruction of vitamin C due to such irradiation.

Since butter, especially winter butter, is relatively poor in vitamin D, practical methods for increasing its potency are under consideration. Either of two methods might be used; namely, irradiation with ultraviolet rays or the addition of small amounts of irradiated ergosterol.

If butter is irradiated, the question of the effect of the ultraviolet rays on its vitamin A content becomes important. In this connection, Steenbock has found that, under conditions designed to develop maximum antirachitic potency, some vitamin A is destroyed. Buy since maximum activation probably is not altogether desirable, he believes that any material destruction of vitamin A in the commercial product need not be feared.

A number of irradiated cereals manufactured under the Steenbock patent are now in the market. These cereals, as they are marketed, are not highly potent, certainly not potent enough, in the amounts usually eaten by the average child, to prevent or cure rickets. Their activity is, indeed, standardized to that degree of potency which  will allow normal bone production when the irradiated cereal is fed as the sole source of cereal in the Steenbock diet 2965 (76 percent of the diet) but not when diluted with three parts of undiluted cereal. “This keeps the cereal definitely in the food class and does not make it a medicine.”

Even Weak Activation Adds Great Value

The value of such weak activation might be questioned by many, but in the words of Tisdall and Brown, “the chief value of irradiated cereals is that irradiation changes them from rickets-producing foods to rickets-preventing foods. As three teaspoonfuls of cod liver oil each day during the winter months does not furnish any great excess of vitamin D over the amount necessary to prevent rickets in the average infant or young child, any means that can remove the rickets-producing tendency of cereals is of value.” Cereal should not be taken in such quantity as to replace important and essential foods.

In case of bread and vegetables the extent of the irradiation in terms of value in comparison to cod liver oil is indicated on the labels.

From The “Vitamins”