Samuel A. Goldblith

Dielectric Properties of Food Materials

ABSTRACTThe factors which affect the dielectric response of food materials are examined in an attempt to establish a predictive model and to obtain a more basic understanding of dielectric properties. Detailed dielectric measurements were performed on rehydrated non-fat dry milk using the precision slotted line technique, at temperatures of 25, 35, 45, and 55°C and at frequencies of 300, 1000, and 3000 MHz. Solute-solute and solute-solvent interaction were found to reduce the dielectric loss factors to levels substantially below those predicted by chemical composition alone; therefore, the dielectric loss cannot be predicted from a linear, additive model based on composition. The results of dielectric measurements of solid food products, beef and turkey were reported. Conductivities of beef juice obtained from cooking were measured and the dielectric losses at 5 to 65°C and 300, 915, and 2450 MHz calculated based on the measured conductivities.

Basic Principles of Microwaves and Recent Developments

Publisher Summary This chapter presents basic principles of microwaves and recent developments and their uses. The first type of microwave process device to be developed was the batch-type oven. Originally, this type of oven operated at 3000 megacycles; now it uses the 2450-megacycle band. The second general type of microwave process device utilizes five 1-2-kw parabolic radiators radiating onto foodstuffs placed on a belt made of a low-loss dielectric material. A continuous-type microwave oven was developed that feeds microwave power from one single large power tube into a tunnel through a series of slit openings. At the end of the belt are energy-trapping devices that serve two functions: (1) they prevent excess radiation from leaking out of the ends of the tunnel, being absorbed in the water loads instead. (2) Being thus absorbed when there is no load in the tunnel, there is no energy to go back into the power tube and damage it. One of the latest developments relates to a folded-waveguide, or meander system, wherein the energy is piped into one end and the product passes through the waveguide. Another (and relatively recent) development is the Amplitron tube. The problem of efficiency of microwave absorption into foods has been approached on a thermodynamic basis, because the sole effect of microwaves in foods is that of heat, and because the amount of heat that can be absorbed is a function of frequency and of the dielectric-loss characteristics of the foodstuffs. The chapter discusses most of the important uses that have been suggested for R F energy in the processing of foods.

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.

Dielectric Behavior of a Semi-Solid Food at Low, Intermediate and High Moisture Contents

AbstractThe dielectric behavior of a semi-solid food was essentially predicted at 3 GHz, 25°C, for a range of moisture contents and water activities, by an electrophysical model for two-phase heter...

Dielectric Properties of Frozen Meats

AbstractFactors that affect the dielectric properties of frozen meats at low temperatures are examined in an attempt to establish a predictive modelling basis for these properties and to obtain a more basic understanding of low temperature dielectric behavior in biological materials. Dielectric constant and loss measurements were made for frozen samples of beef, chicken breast, chicken thigh, pork and turkey roll using a short-circuited coaxial line technique at temperatures of -20° and -40°C and frequencies of 300, 915 and 2450 MHz, These measurements suggest the presence of significant amounts of free water and dissolved ions at low temperatures. Dielectric properties of the frozen meats were generally predicted by a physical-chemical model involving pockets of saturated aqueous sodium chloride suspended in a field of solids and ice at thermodynamic equilibrium.

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.

Some Considerations in the Processing of Potato Chips

AbstractThis paper presents data on the effects of varying moisture contents on the dielectric properties of potato chips measured at two frequencies and at three temperature levels. It reviews some of the literature on the dielectric properties of foods and points out the difficulty in making predictions and the need for measurements on dielectric properties of foods. It points out the known facts that in this area, technology has preceded fundamental science and presents the premise thot if sufficient work on the fundamental aspects of microwaves and their interactions with foods are available, better processing equipment designed on experimentally obtained parameters could be built thus putting the industry on a much sounder fundamental basis.

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.

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.

The Microbiology of Freeze-Dried Foods

Publisher Summary In this chapter, the microbiology of freeze-dried foods is discussed in detail. The refrigeration of freeze-dried foods is unnecessary; rehydration is rapid; shrinkage is minimal; chemical activity is appreciably deterred (especially if stored at 20°C. or lower); since most of the water is removed a considerable savings in weight is achieved; and, if properly processed and packaged, microbial multiplication is virtually eliminated during storage. At the present time, these advantages must be balanced against the additional increment of cost incurred by this process and a loss in certain quality characteristics. It can be expected that both of these factors will receive greater attention from the food industry, and, as product improvement is achieved and cost lowered, the application of freeze-drying as a technique for food preservation will be increased. Although one cannot presume that freeze-drying will be a major method of food preservation, the volume of freeze-dried foods should be appreciable and the microbiological aspects of freeze-dried foods must be properly evaluated so that standards might be promulgated.