Bernard E. Proctor

Electromagnetic radiation fundamentals and their applications in food technology.

Publisher Summary This chapter covers the known applications of electromagnetic energy in the field of food research within the past ten years, from sonic vibrations at one end of the spectrum to gamma rays at the other end. For orientation, some reference has been made to previous applications. An illustrative chart of the electromagnetic spectrum has been presented. This chart shows the approximate locations, in the electromagnetic spectrum, of the various types of radiation discussed in this chapter. In an effort to make a logical presentation of the known applications of electromagnetic energy in the food field, the various types of electromagnetic radiation have been discussed. The chapter is concerned with the applications of various types of radiation, the uses and the potentialities of each specific type have been discusses independently. This chapter intends to indicate to other investigators the progress in the application of electromagnetic radiations in food processing.

Some microbiological aspects of radiation sterilization

Abstract Pure suspensions of bacteria, Escherichia coli, Bacillus subtilis, B. thermoacidurans, and several putrefactive anaerobes denoted as PA #76H and PA #3679 (species related to Clostridium sporogenes), were irradiated both by cathode rays and by gamma rays from cobalt-60. These studies emphasize that broad generalizations are not possible on the effects of different environments on the radiosensitivity of a bacterial population. When a free-radical acceptor such as sodium ascorbate was added to saline suspensions of B. subtilis, the radioresistance of the organism was increased, but when sodium ascorbate was added to saline suspensions of PA #76H, PA #3679, and B. thermoacidurans, the radioresistances of these organisms were no different from those when they were irradiated in saline solution alone. All these organisms (B. subtilis, B. thermoacidurans, PA #76H, and PA #3679) were more radioresistant when irradiated in the presence of sodium ascorbate in more complex media such as pea puree and tomato juice. Comparisons of the radioresistances of these organisms in saline solution and in a more complex medium also show differences. B. subtilis was less radioresistant, whereas B. thermoacidurans, PA #76H, and PA #3679 were more radioresistant in a more complex medium than in a saline solution. The effects of pH, the atmosphere during irradiation, the type of radiation, and the state of the medium on the radiosensitivities of these organisms are discussed. Recent data on the putrefactive anaerobes are presented to illustrate the handling of data and the statistical method utilized. Considerations are given for examining heterogeneous populations of bacteria encountered in various foods to be irradiated.

Radiosensitivity of Bacillus subtilis under different environmental conditions.

Research has been under way for several years in a number of laboratories to modify the radiosensitivity of microorganisms when exposed to ionizing radiations (1-13). The susceptibility of E. coli to destruction by ionizing radiations and the ease with which its radiosensitivity can be modified by physical and chemical means have been investigated by Hollaender and his associates (3, 5, 6). More recently the results of an extensive study on this organism have been published by these laboratories (4). The investigation reported in the present paper was undertaken to ascertain the degree to which the radiosensitivity of a spore-forming aerobic bacterium, Bacillus subtilis, can be modified by environmental factors.

Some effects of ionizing radiations on lipids. I. Monocarbonyl production in vegetable oils

Summary and ConclusionsIrradiation of refined vegetable oils by high-energy cathode rays resulted in the production of monocarbonyl compounds. The yield was about 0.2 µM per gram per 106 rep. for doses up to about 107 rep. Some of the products were themselves sensitive to the radiations, and the net yield was dependent upon a function of the concentrations and reactivities of the precursors and of the end-products.Concurrently with the formation of the monocarbonyls there was an attack on the conjugated triene systems in the media and an increase in ultraviolet absorption in the 225–240 mµ region. However the irradiation products resulted from other mechanisms in addition to those involving the trienes.Irradiation under reduced temperature or in vacuum or with the addition of antioxidants did not decrease the yield of monocarbonyl compounds. However the use of a vacuum and the inclusion of antioxidants were partially effective in reducing the irradiation attack on triene groups.The net yields of monocarbonyls were dependent upon the concentrations and sensitivities of the products as well as of their precursors. Thus, although methods commonly successful in inhibiting oxidations of oils did not reduce these yields, they did suppress some irradiation-induced reactions, particularly those involving unsaturated compounds. In this respect their action was similar to that which has been demonstrated in inhibition studies of antioxidations in oils.

Trans-isomerization of oleic acid and potassium oleate by ionizing radiation

SummaryThe oleic acid of IV 89.2 was irradiated with cathode rays at doses of 15 × 106 to 70 × 106 rep and was found to have beentrans-isomerized from 2.5% at 45 × 106 rep to 9.4% at 70 × 106 rep; the oleic acid of IV 89.8 irradiated at doses of 13.4 × 106 to 401.6 × 106 rep and was found to have beentrans-isomerized to 4.9% at 187.4 × 106 rep and to 14.6% at 401.6%.Thetrans-isomerization was independent of oxygen.Aqueous solutions of potassium oleate at 1% concentration were irradiated with doses from 1 × 106 rep to 5 × 106 rep. The oleic acid recovered from the irradiated solutions was found to have beentrans-isomerized from 8.1% at 1 × 106 rep to 1.9% at 5 × 106 rep; the oleic acid recovered from the 2.5% solutions was found to have beentrans-isomerized to 8.3% at 5 × 106 rep, 11.9% at 10 × 106 rep, and 0.1% at 30 × 106 rep.A modified “baseline” technique in infrared spectrophotometric analysis is described.

Studies on the Dosimetry and Bactericidal Effects of Gamma Radiations from a Cobalt60 Source

Since 1943 the Department of Food Technology at the Massachusetts Institute of Technology has been conducting studies on the effect of ionizing radiations, produced by particle accelerators, on microorganisms. The object of these studies has been to investigate the fundamental changes involved and, if possible, to establish a basis for ascertaining the feasibility and the practicability of sterilization of foods without the application of heat. Since 1950 research has been underway in these laboratories to evaluate the possibility of utilization of waste fission products as sources of radiation. As a source of ionizing radiations a kilocurie of cobalt60, a “mock” fission source, has been prepared by the Reactor Division at the Brookhaven National Laboratories. The use of cobalt60 for experimental studies is predicated at this time on (a) the ready availability of cobalt60 in multicurie source form and (b) its desirable and well defined physical characteristics of energy, half-life, and the like. As this i...

Some further studies on the application of methylene blue in aqueous solution as a dosimeter for intense beams of high-energy radiation.

Abstract Aqueous solutions of methylene blue sealed in glass ampoules have been exposed to γ-radiation, stored at different temperatures and checked periodically for dye retention for a period of 2 months. The results obtained show that the dye destruction proceeds after irradiation and at a rate dependent on the storage temperature. Parallel tests conducted with non-irradiated samples show small losses of dye, of the order of the experimental error. Another set of experiments using electron beams revealed no practical differences in the extent of dye destruction when the temperature during the irradiation process was varied from 45 to 150°F. Some practical recommendations are given in order to attain a good degree of reproductibility when using the methylene blue as a radiation dosimeter. In summary also, it may be stated that this dosimeter is of value for routine evaluation of electron and γ-ray beams for: 1. (1) It has a first order dose response which is linear to at least 6 × 10 6 rep (using a 1000 mcg/ml solution from 1 × 10 6 to 6 × 10 6 rep). 2. (2) It is easily measured using common laboratory colorimeters. 3. (3) It is temperature independent above the freezing point of water. 4. (4) It is stable for 1 week at refrigerator temperatures.

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-