Dielectric Properties Of Foods Research Articles

Radio frequency food processing. Current status and perspectives – a review

The present review provides a critical overview of the current status and prospects for the development and application of radio frequency food processing. The mechanism of action of radio frequency treatment, the dielectric properties of foods, the mechanisms for inactivating microorganisms and endogenous enzyme systems, the sensory and physicochemical changes occurring in radio frequency treated foods, as well as the application of radio frequency treatment in the food industry are discussed. Radio frequency processing technology has been found to have some advantages over conventional heat exchange systems in terms of time savings, higher profitability and better efficiency. In the available literature, the conducting of additional studies regarding the package violation and its permeability and integrity during radio frequency processing were discussed. Radio frequency heating has been shown to effectively eliminate pathogens and preserve better, physicochemical and sensory properties of food products compared to conventional heating due to shorter processing time. It is concluded that radio frequency energy heating is suitable for processing packaged foods that remain safe and stable during storage. For these reasons, it is concluded that radio frequency food processing has a very bright future.

Effect of Beverage Composition on Radio Frequency Identification (RFID) Performance Using Polyethylene Terephthalate (PET) Bottles for Smart Food Packaging Applications.

Radio frequency identification (RFID) technology is crucial in revolutionizing the food supply chain and combating global food waste. However, this technology faces challenges in full integration due to disruptive effects on tags caused by the dielectric properties of food and beverage ingredients, chemical constituents, and their packaging. This paper aims to demonstrate the effect of packaging and beverage contents on RFID tag performance. Three commercially available ultra-high frequency (UHF) RFID tags with different designs were tested on polyethylene terephthalate (PET) bottles, measuring tag performance through sensitivity, backscatter, and read range in the presence of various water-based solutions and commercially available beverages. The results highlight the substantial impact of the beverage type and tag design on RFID performance. The results of this study showed that tag 3 was the most consistent and readable tag amongst those tested in the presence of different beverage contents. Tag 3 resulted in a sensitivity ranging from -0.49 to -2.01 dBm, backscatter from -38.16 to 43.59 dBm, and read range from 1.58 to 1.88 m, while tag 1 performed the best in the presence of an empty PET bottle resulting in a sensitivity of -20.78 dBm, backscatter of -23.65 dBm, and read range of 16.34 m. The results of this study can be used for further investigations to develop a mathematical model that predicts the RFID tag performance based on the food composition. This model will be helpful for the design of the tags while facilitating the adoption of smart packaging for food traceability.

Development and validation of analytical charts for microwave assisted thermal pasteurization of selected food products

For process development using an industrial Microwave Assisted Thermal Pasteurization System (MAPS), it is desirable to have effective tools that allow accurate prediction of heating rates in pre-packaged foods. This research aimed to develop engineering charts that illustrate the relationships among the dielectric properties of foods, preheating temperature, product thickness and heating rate for microwave heating in MAPS. We selected three different foods, namely mashed potatoes, peas, and rice, in this study. Three complementary G-T (Gezahegn-Tang) charts were developed using MATLAB software by applying Maxwell's and heat transfer equations with measured physical properties of the selected foods. Experiments were conducted with mashed potato samples using a pilot-scale MAPS unit to validate the charts. The temperature profiles measured at the cold spots of the food samples in the microwave heating section of MAPS were positively correlated with predicted temperatures from the chart (R2 > 0.96); more than 95% of the standardized residuals were in the range of −2 to 2 °C. The charts are able to estimate microwave heating rate at the cold spots in food packages based on food dielectric properties and package thickness. They can also be used to help select an optimal preheating temperature for the maximum heating rate. This research demonstrated the possibility of using validated G-T charts to assist food companies in developing pasteurization schedules based on MAPS for the commercial production of different packaged ready-to-eat (RTE) meals.

Advances in radio frequency pasteurisation equipment for liquid foods: a review

SummaryRadiofrequency (RF) heating is an alternative emerging technology to conventional thermal methods; it has been employed for food pasteurisation, providing fast and volumetric heating. However, non‐uniformity in the heating pattern has been reported. RF pasteurisation has been studied in different liquid foods. This review provides information about the RF heating mechanism and equipment used to pasteurise liquid food to control deteriorative or pathogen micro‐organisms and the effect of the RF treatment on the quality of liquid foods. Developing an effective RF pasteurisation for liquid foods requires knowing the food dielectric properties, which determine the heating uniformity, temperature distribution and heating rate. The efficiency of continuous RF heating systems could depend on the fluid rate, resident time and absorbed power. RF heating can pasteurise liquid food, decrease microbial population and preserve the product's nutritional and physicochemical quality.

A simplified approach to assist process development for microwave assisted pasteurization of packaged food products

The purpose of this study was to develop a convenient method to assist the food industry in developing process schedules for production of ready-to-eat meals using microwave assisted pasteurization system (MAPS). An analytical model was applied to estimate the temperature increase in the cold zone in packaged foods during heating in a 915 MHz single-mode microwave system. This model was validated in a pilot-scale four-cavity MAPS using mashed potato-gellan gum model food with different thicknesses (22 to 36 mm) and salt contents (0.0 to 1.0%). Mobile sensors were placed in the packages to measure temperature at the pre-determined cold spots. For 2.48 min of microwave heating with 5, 5, and 8.7 kW 915 MHz microwave powers, the highest temperature increase at the cold spot during microwave heating was 33.2 °C in the 22 mm thick model food with 0.6% salt content, whereas the lowest temperature increase was 10.3 °C in the 36 mm thick model food with 1.0% salt content. There was a deviation of 1.9 ± 1.2 °C between experimental and predicted data with an R2 of 0.89. A simplified chart was developed based on the validated analytical results to allow rapid prediction of temperature increases in MAPS as influenced by food dielectric properties and package thickness. Examples were used to illustrate how the chart could assist in process scheduling. The chart can help assess the heating rates of various pre-packaged food products in a specific industrial MAPS or guide product development for desired heating uniformity.

Use of Modern Regression Analysis in the Dielectric Properties of Foods.

The dielectric properties of food materials is used to describe the interaction of foods with electromagnetic energy for food technology and engineering. To quantify the relationship between dielectric properties and influencing factors, regression analysis is used in our study. Many linear or polynomial regression equations are proposed. However, the basic assumption of the regression analysis is that data with a normal distribution and constant variance are not checked. This study uses sixteen datasets from the literature to derive the equations for dielectric properties. The dependent variables are the dielectric constant and the loss factor. The independent variables are the frequency, temperature, and moisture content. The dependent variables and frequency terms are transformed for regression analysis. The effect of other qualitative factors, such as treatment method and the position of subjects on dielectric properties, are determined using categorical testing. Then, the regression equations can be used to determine which influencing factors are important and which are not. The method can be used for other datasets of dielectric properties to classify influencing factors, including quantitative and qualitative variables.

Effect of changes in salt content and food thickness on electromagnetic heating of rice, mashed potatoes and peas in 915 MHz single mode microwave cavity

A mathematical model for predicting electromagnetic power dissipation within a rectangular dielectric slab heated by equal intensity 915 MHz plane waves from top and bottom was developed. A dimensionless parameter (J-T number) which is a combination of the loss factor (εr″), dielectric constant (εr′) and food thickness (L) was proposed. This unique number provided direct insight into the relationship between food dielectric properties, thickness, product temperature, and thermal lethality. For the validation tests, mashed potatoes, peas and rice samples with 0–2% salt content were processed in a pilot scale microwave assisted thermal sterilization (MATS) system. In each food, the combination of dielectric properties and thickness which gave J-T number of 1.8–2.2 at 100–121°C, provided the highest lethalities. MATS is a novel commercial technology being adapted in the food industry. A qualitative assessment of the combined effect of food properties on lethalities using this model will be helpful in process development for MATS systems.

Dielectric Properties of Food and Microwave Heating

Dielectric Properties of Food and Microwave Heating

HEATING UNIFORMITY AND RATES IN A DOMESTIC MICROWAVE COMBINATION OVEN

ABSTRACT Physics‐based modeling complemented with magnetic resonance imaging (MRI) for validation can provide a novel means to understand and thereby optimize combination heating processes. The objectives of this study were to compare heating patterns in a combination of radiant, forced air and microwave oven measured by MRI with those predicted by coupled electromagnetics‐heat transfer model; quantify speed and uniformity of heating for the different combination modes; determine the effect of food dielectric properties on heating patterns; and delineate the nature of individual heating modes and their combinations. The modes of radiant heating through heating elements and forced convection by fan led to a more uniform heating compared with the faster (but less uniform) heating method provided by the microwaves. Combination methods were faster than radiant, forced‐air and microwave‐only heating. Although the speed of heating increased appreciably for combination modes, the nonuniformity of heating did not increase as much. PRACTICAL APPLICATIONSThe results from the study can be used to develop design recommendations/guidelines for combination heating for different thermal processes such as baking, broiling, roasting and reheating of different materials, grouping them based on their properties. The research can benefit the consumers, food services and equipment manufacturers to understand the combination heating process in a better way and to, thereby, use it efficiently. Without a fundamental understanding of the effect of various combinations, optimization of heating can be intractable. The fundamental approach used in this study would, therefore, help consumers and food services in preparation of safe and high‐quality foods through combination heating. The work would also help equipment manufacturers in optimizing the designs of combination‐heating ovens.

Role of lateral and radial irradiations on efficient microwave processing of food cylinders

A detailed theoretical analysis has been carried out to assess the role of lateral and radial irradiations on microwave heating of 2D cylinders for beef and oil samples. The lateral irradiation may represent the sample incident at one direction and the radial irradiation refers to sample exposed to uniform microwave intensities at all directions. For both lateral and radial irradiations, the effective microwave incidence from the source is assumed to be identical. A preliminary analysis on microwave heating of samples has been shown via average power within a sample vs sample radius for beef and oil samples. The samples with smaller radius are found to have larger average power with radial irradiation for both beef and oil samples. The hot spot formation within a sample is found to be a strong function of lateral/radial irradiation for various food dielectrics. The radial irradiation is found to be not favorable especially for large oil samples where the hot spot occurs at the center resulting in larger thermal gradient that contrasts earlier works which established that the radial irradiation minimizes the thermal gradient irrespective of sample size. The present work provides guideline on heating policy based on either lateral or radial irradiation depending on sample size and food dielectric properties.

Measurements of the Dielectric Properties of Cheddar Cheese

An experimental study of the dielectric properties of cheddar cheese at microwave frequencies has been made at 20 °C. Measurements were made using rectangular waveguide transmission line cells in five frequency bands from 750 MHz to 12.4 GHz. The physical and chemical properties of the cheese were also measured and correlations with the dielectric properties were investigated. Cheddar cheese was chosen for this study because it is a homogeneous product which allows accurate dielectric measurements to be made. This makes it a useful product for testing models which predict the dielectric properties offoods based on knowledge of their chemical and physical properties.

Dielectric Behavior of an Aqueous Cation Exchange

High-frequency dielectric constant and loss measurements for suspensions of an aqueous cation exchange resin (Biogel CM 30) in deionizedwater were predicted by the Debye models for pure polar solvents, as modified for water binding and conductivity effects of the ionizable particle suspensions. Predictions, basedonfree sodium equivalents without colloidal swface charge effects, agreed very closely with standing wave measurements at a 3 GHz and 25°C. Measurements from 50 to 200 KHz also suggested regions of dispersion similar to those of mammalian red blood cells. These results are consistent with the concepts of the Donnan equilibrium and Stern-Gouy double layer as a basis for the “suspension effect” observed by many researchers in aqueous suspensions of acid soil samples. The results also suggest that colloidal swface charge effects on cell walls and membranes of foods are negligible in predicting food dielectric properties, as compared with the dipole rotation of free water and the conductive migration ofdissolved ions at microwave frequencies.

PREDICTION ON THE RELATIVE DIELECTRIC LOSS FACTOR IN AQUEOUS SOLUTIONS OF NONFAT DRIED MILK THROUGH CHEMICAL SIMULATION

SUMMARY— The relative dielectric loss factor in aqueous solutions of nonfat dried milk has been studied through chemical simulation of its major constituents. This study shows that milk dielectric loss cannot be predicted simply on the basis of its chemical composition. It does, however, provide a conceptual basis for milk modeling which leads to a more general understanding of food dielectric properties. The focal point in milk simulation was shown to be a complex relationship of solute‐solute and solute‐solvent interactions which reduce the dielectric loss factors to levels substantially lower than those predicted by considering only chemical composition. These include both binding and nonbinding interactions of the solutes. The binding effects are believed to result from the incomplete dissociation of milk salts in a saturated ionic environment and are reflected by a reduction of specific ion activities in solution. Nonbinding effects, on the other hand, are seen to result from the formation of hydrated ion complexes. These effects, in conjunction with chemical composition, are shown to completely determine the dielectric loss level in dried milk solutions.

Dielectric Properties of Food at 3 GHz as Determined by a Cavity Perturbation Technique.

After a preliminary study of various methods for dielectric measurements described in the literature, a cavity perturbation method was chosen and developed for measurements on food materials at 3 GHz. A cylindrical TMO 10-cavity was designed for measurements on low-loss materials and a TMO 12-cavity for materials of high loss. Both permit favorable sample dimensions, simple insertion of samples in glass or quartz tubes, and rapid measurements of a number of replicates. The dielectric constant and loss factor are calculated from the shift in resonant frequency and Q-value or transmission between empty and filled sample tube.

Dielectric Properties of Foods at 3 GHz as Determined by a Cavity Perturbation Technique.

AbstractA series of measurements of dielectric properties for food materials were made in the temperature range —20 to +60°C using the cavity perturbation technique described in the first paper of this series. Variables studied besides temperature were preparation technique, pretreatment and composition of the food materials. Results obtained were consistent, reproducible and in fair agreement with literature data available.For moist foods a very sharp rise in dielectric properties is seen during thawing, followed by a gradual decrease with further temperature increase, except for salted foods where a continued increase with temperature in loss factor was found. A clear positive correlation between water content and e′r was found but not for er.Dielectric properties decreased with increasing fat content, and loss factor increased with salt content. In general, freezing, short time frozen storage, thawing and rate of heating had little influence on the data determined, with the exception of thickened grav...

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.