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Microwave heating is gaining relevance for cooking processes with faster heating speeds, shorter processing times, and lower environmental impact than traditional heating (gas or electric ovens for bakery products). Dielectric properties of cookies dough (16.9% moisture content and 19.5% fat content, w.b., density of 650 kg/m3) were analyzed for temperature (18–80°C) and microwave frequency (0.5–2.5 GHz). The penetration depth was calculated, and with the obtained results, the maximum thickness values for the cookies were 1.61 and 0.73 cm for 915 and 2450 MHz, respectively, to ensure enough wave penetration. The dough was cut into 8 ‐cm‐diameter and 0.7 ‐cm‐thickness pieces and MW baked at 360 W for 1.5 min. MW‐baked cookies were compared with cookies from the same dough baked in an electric oven at 160°C for 12 min, being similar. MW baking time was shorter, which means the method has potential for this kind of dough. Practical applications: DPs are key factors in developing processes, simulation, and modeling employing MW heating. The MW process time is short and produces a lower environmental impact than conventional baking. MW ovens at the industrial level are available in the market to scale up the assays at the lab level (2450 MHz and small amounts). For this kind of dough, the possibility of getting MW‐baked cookies is real. [ABSTRACT FROM AUTHOR]

Summary: Radiofrequency (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. [ABSTRACT FROM AUTHOR]

Dielectric properties (DPs) of fresh rabbit meat in the microwave range (0.5 to 20 GHz) were determined. Three different muscles (Biceps femoris, Tensor fasciae latae, and Longissimus thoracis) from California rabbits (male and female) were measured with the open‐ended coaxial probe method at temperatures of 20, 40, and 60 °C. To assess the possible effect of age, females of 100 and 180 days old were analyzed. DPs were affected by frequency, muscle type, age, gender, and temperature (p < 0.05). Dielectric constant decreased with increasing frequency. Loss factor decreased from 0.5 to 2.5 GHz due to ionic conduction, followed by an increase up to 20 GHz, dominated by dipolar relaxation. Practical Application: These results are key parameters for further quality sensing applications and for heating processes of meat rabbit using microwaves. Longer penetration depths were achieved at 915 MHz; this frequency is recommended for further applications. Besides, dielectric properties have potential to be a tool for identification of gender and age for slaughtered rabbits. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric properties (DPs) of two beverages, tamarind and a green drink (based on mix fruits of pineapple, guava, lemon, and nopal), were studied. The DPs were determined using the open‐ended coaxial probe method in the frequency range from 0.25 to 25 GHz at 10, 30, 50, and 70 °C. The dielectric constant decreased when both frequency and temperature increased above 1000 MHz. For both beverages, the dielectric loss factor increased with increasing frequency and increasing temperature. In addition, dielectric constant values ranged from 59.7 to 82.5, and the dielectric loss factors were between 5.8 and 31.1. The penetration depth (dp) of electromagnetic waves in the beverages increased proportionally to temperature at frequencies above 1000 MHz; dp values ranged from 0.2 to 7.5 cm. Because of its complexity and the amount of ingredients and the interactions between them, the green drink showed higher values of dielectric constants in comparison with the tamarind beverage. Practical Application: The dielectric properties of the studied beverages, how they behave at different temperatures, and the penetration depth reached by microwave at the allocated frequencies, provide important parameters for further heating treatments, such as heating (microwave‐assisted pasteurization) and for modeling/simulation purposes. [ABSTRACT FROM AUTHOR]

In this work, an open-ended coaxial probe was used to characterize the dielectric properties of different tequilas and agave-distilled spirits in the range from 500 MHz to 20 GHz. The alcohol content of these beverages was clearly identified at these frequencies. From a Cole-Cole plot, the relaxation time (τ) was extracted and it was observed that there was a linear correlation between alcohol content and τ, where lower t corresponds to lower ethanol content. In addition, dielectric differences were also found between silver, aged, and extra-aged tequilas. As aging increased, the real and imaginary parts of the permittivity increased (p < 0.05). These findings offered a new method for detecting alcohol content in tequila as well as for identifying tequila aging. [ABSTRACT FROM AUTHOR]

Dielectric properties (DPs) of selected fruits: guava (Psidium guajava), mamey sapote (Pouteria sapota), red prickly pear (fruit from Opuntia streptacantha), and white prickly pear (fruit from Opuntia ficus-indica), as well as nopal (young cactus pads or cladodes from Opuntia ficus-indica) were studied. DPs were determined using the open-ended coaxial probe method at microwave frequencies (500 MHz-2 GHz) and temperatures of 20, 40, and 60ºC. At 20ºC and 915 MHz for unripe fruits, dielectric constant values ranged from 65.7 to 70.9, while the loss factor had values between 8.4 and 20.7. Both dielectric constant and dielectric loss factor were affected by temperature and frequency (p < 0.05). For example, loss factor for red prickly pear at 2450 MHz decreased from 13.88 at 20ºC to 12.8 at 40ºC and 11.7 at 60ºC. DPs of fruits were also affected by their ripening (quantified through the maturity index). In addition, penetration depth decreased with increasing frequency, ranging from 1.98 to 4.80 cm at 915 MHz and from 0.25 to 0.41 cm at 5800 MHz. Results are valuable to develop further applications with microwave technology for these foods, such as microwave-assisted disinfestation treatments or microwave drying. [ABSTRACT FROM AUTHOR]

Dielectric properties of common Mexican beans (Phaseolus vulgarisL.) were determined and analyzed at microwave frequencies (800–2500 MHz). The free-space transmission technique was employed for the measurements of three varieties (“Flor de mayo,” “Bayo,” and “Negro”) with different moisture content (8.8–12.3%, w.b.) at 20, 30, 40, 50, and 60°C. The dielectric constant and loss factor of beans decreased with increasing frequency for a fixed temperature, and increased with increasing temperature at a fixed frequency. The dielectric constant increased with increasing moisture content, while the loss factor remained nearly constant. With these results, disinfestation or quality control measurements can be proposed for beans using microwaves. [ABSTRACT FROM AUTHOR]

Dielectric properties of three varieties of common beans (Phaseolus vulgaris L.) were determined at Ultra-Wideband (UWB) frequencies (3-10.6 GHz) using a free space transmission method. Beans were conditioned to get different moisture contents; the bulk density of beans (ρ) increased at higher moisture contents. Permittivity and conductivity of beans also increased with moisture content. The dielectric constant (ε') remained practically constant in the studied frequency range, while loss factor (ε") decreased in frequency. The ε'/ρ vs ε''/ρ complex-plane plot (Argand diagram) was built and a linear trend was observed, with positive slope. However, this slope value decreased at higher frequencies. [ABSTRACT FROM AUTHOR]