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

Abstract

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.

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

“…The ε” of the beverages at ISM frequencies at different temperatures are listed in Table . ε” increased with increasing frequency, in agreement with the reports of some authors in nopal and guava fruit (Kataria, Olvera‐Cervantes, Corona‐Chávez, Rojas‐Laguna, & Sosa‐Morales, ).…”

“…The trend of decreasing d p versus frequency and temperature was also reported by Kataria et al. () in guava fruit and nopal ; and by Zhu et al. () for grape, pear, orange, apple and pineapple juices.…”

“…The ε" of the beverages at ISM frequencies at different temperatures are listed in Table 2. ε" increased with increasing frequency, dielectric loss factor (ε ), and penetration depth (d p ) of tamarind and green beverage at ISM frequencies (915, 2,450, and 5,800 MHz) in different temperatures (10, 30, 50, and 70°C in agreement with the reports of some authors in nopal and guava fruit (Kataria, Olvera-Cervantes, Corona-Chávez, Rojas-Laguna, & Sosa-Morales, 2017b). The highest ε" value among beverages was 37.75 obtained at 11.25 GHz and 10°C for green beverage in comparison to the tamarind beverage.…”

Dielectric properties of chili powder in the development of radio frequency and microwave pasteurisation

“…The similar results were found in different studies of other materials. [14,27,36,37] Lower penetration depth will lead to more surface heating which can seriously affect the uniformity of RF or MW pasteurisation. Higher penetration depth means more uniform electric field distribution and better heating uniformity.…”

“…Food products are dielectric materials that can store energy like a capacitor and dissipate energy like a resistor in the electromagnetic field. [14] The ability to store and dissipate electromagnetic energy is described as dielectric constant (ε') and dielectric loss factor (ε"), respectively. The dielectric properties (ε) are combinations of dielectric constant and loss factor, which can be described as a complex number as shown in Eqn.…”