J. T. R. Nickerson

Freezing and Irradiation

ALTHOUGH THE preservation of foods by freezing has been an established commercial enterprise since the early 1930s of this century, it is a comparatively new industrial method of food processing. The quantity of frozen foods produced each year has increased greatly during the last decade and greater increases are indicated for the future. Frozen foods are not sterile and if grossly mishandled may serve as a medium for the growth of bacteria of the numerous types usually present. Eventually, under such conditions, foods may become decomposed or support the growth of bacteria which might be detrimental to health. For this reason, at various times since quick freezing was introduced, the significance of frozen foods in transmitting disease has been a controversial subject. A method of food processing involving the treatment of comestibles with ionizing radiations has been developed in recent years. While this process has not yet been used commercially, there is some possibility that it may have industrial application to foods within the next decade. As with frozen products, the manner in which the public health is affected by the ingestion of foods preserved by irradiation treatment should be given thorough consideration. Of greatest importance to public health regarding frozen foods is the possibility that those foods, which would serve as suitable media, might be handled in such a manner as to provide for the growth of Clostridium botulinum, Micrococcus pyogenes var. aureus, or bacteria of the Salmonella group. Other bacteria may be the cause of food intoxications or food infections, but most frequently the bacterial groups previously named have been involved. The bacteria in foods are destroyed to some extent by freezing and during storage at temperatures below freezing. While this is the case, it is well known that freezing and normal storage periods at temperatures below freezing do not destroy all bacteria, even of the types which cause food-borne epidemics, which may be present in foods. Cl. botulinum, Staphylococci, and the Salmonella bacteria will not grow in foods which are held in the frozen state. If, therefore, frozen foods become associated with the transmission of diseases, growth of the bacteria involved must have taken place prior to freezing or after the product was defrosted. Concerning the growth of Cl. botuli-