Dielectric properties of guava, mamey sapote, prickly pears, and Nopal in the microwave range

Dielectric properties of fresh rabbit meat in the microwave range

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.

Dielectric properties of Mexican sauces for microwave-assisted pasteurization process

The dielectric properties and specifically the complex relative permittivity of foods are key elements for the design of pasteurization processes with high frequency electromagnetic waves. Mexican sauces are recognized worldwide for their flavor and nutritional properties. In this work, the complex permittivity of four of the most representative sauces of Mexican cuisine (chipotle chili, habanero chili, red and green sauce) is presented. The permittivity was measured with the open coaxial probe method at temperatures of 25, 40, 55, 70, 85 °C and in the frequency range of 500 MHz to 6 GHz. Additionally, moisture content, specific heat, viscosity, water activity, density and electrical conductivity are reported, these last three at 25 °C. Dielectric properties were affected by the sauce formulation. The loss factor of each sauce sample at any temperature presents significant changes in relation to the frequency. At 915 and 2,450 MHz, d ε ' ' d T > 0 , which would cause a thermal runaway effect or the uncontrolled rise in temperature in the sauces during the microwave pasteurization. At 5,800 MHz, d ε ' ' d T < 0 , which would give better control for microwave heating than at 915 and 2,450 MHz. At 915 MHz, the loss factor of all sauces is higher than at 2,450 and 5,800 MHz, therefore, more rapid heating can be produced. Moreover, at 915 MHz, microwaves exhibit higher penetration depth than at 2,450 and 5,800 MHz; therefore, at 915 MHz, the greatest uniform microwave dielectric heating would be achieved. Thus, 915 MHz is the frequency recommended for the studied sauces pasteurization. PRACTICAL APPLICATION: This work provides the dielectric properties of Mexican sauces at different temperatures and their penetration depths in the microwave range, which are key information for further microwave-assisted pasteurization process and for getting safer sauces for consumers. Moreover, this research supplies suggestions about what frequency for ISM (Industrial, Scientific and Medical) applications is the best for microwave-assisted pasteurization according to the penetration depth of the electromagnetic wave in the sauces and microwave dielectric heating speed of the sauces.

Dielectric properties of litchi fruit (Litchi chinensis Sonn) at microwave frequencies

The dielectric properties of litchi fruit were determined using the open-ended coaxial probe method. The measurements were performed in the frequency range from 0.5 to 20 GHz during 3 days of storage at room temperature (~  24 °C). The dielectric properties increased with storage time. Additionally, measurements at different temperatures (24, 30, 40 and 50 °C) were determined. The dielectric constant (ε') decreased with increasing temperature in a frequency range of 0.5-5 GHz; at higher frequencies, ε' increased with increasing temperature. The loss factor (ε″) value increased at frequencies higher than 2 GHz and decreased with increasing temperature. The results will be useful for further applications using microwaves, such as microwave-assisted drying, sensing of quality parameters, modeling, and heating to protect against molds or insects, among other applications.

Effect of temperature and moisture contents on dielectric properties at 2.45 GHz of fruit and vegetable processing by-products

If processing alters the food-waste composition, dielectric properties are affected and need to be determined for efficient microwave processes.

Dielectric Properties of Beverages (Tamarind and Green) Relevant to Microwave-Assisted Pasteurization

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 (d_p ) of electromagnetic waves in the beverages increased proportionally to temperature at frequencies above 1000 MHz; d_p 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.