The dielectric properties of tylose water pastes during microwave thawing and heating were measured over 300–3000 MHz and −30 to +60 °C, and the feasibility of their use as a frozen model food instead of frozen lean tuna was evaluated. The effects of salt (NaCl) content (0.5–2.0%, wb) on the dielectric properties were investigated. Although salt is a good additive for increasing the dielectric loss factor, higher salt addition increased the thawing time and non-uniformity through decreased penetration depth. A similar response to increasing temperature between frozen lean tuna and tylose paste was observed during MW thawing and heating at 2450 MHz, due to similarities in penetration depth. This was possible by an appropriate adjustment of the dielectric properties of tylose by salt addition (0.5% NaCl). This study confirmed the potential of frozen tylose paste as a model food in evaluating performance of microwave thawing of real foods.

Plants and algae are the main sources of natural bioactive compounds used in the food and pharmaceutical industries. It is very important to achieve an efficient and safe technique to recover bioactive compounds while maintaining their quality and properties. Subcritical water extraction is the most promising engineering approach that offers an environmentally friendly technique for extracting various compounds from plants and algae. Application of pressurized water and high temperature in subcritical phase is able to modify the dielectric constant and polarity of the solvent which then contributes to a better extraction process. The technique improves the mass transfer rate and preserves the biological potency of the extracts. This article reviews current studies on the extraction of bioactive compounds from various species of plants and algae using the subcritical water technique and discusses its effects and benefits for the food and pharmaceutical industries.

There is currently no recognised equation, or set of equations, that can be used to adequately describe moisture dependant dielectrics. This study addresses this issue so that moisture dependant dielectric properties can be directly input into drying models, where the microwave or radio frequency source is always limited to a single frequency. This was achieved by adapting water activity equations to describe the moisture dependant behaviour of the loss factor and the dielectric constant of hygroscopic inhomogeneous materials at microwave and radio frequencies. These equations were fitted to thirty moisture dependant loss factor and dielectric constant data sets. The adapted water activity equations proved to be very effective at describing dielectric behaviour, with the best equation fits to the thirty moisture dependant dielectric data sets having an average Mean Relative Error of 2.99%. The suitability of the equations are discussed, and specific equations are recommended for fitting to different types of moisture dependant dielectric response.

The evolution of dielectric properties of starch-based food pellets with different moisture contents was measured during microwave expansion to determine the effect of water content on the expansion dynamics.Dynamic dielectric measurements were found to be an excellent procedure to in situ monitor and characterize the different stages in the material transformation of food pellets during microwave expansion.Although the maximum bulk expansion of pellets was achieved at a moisture content of approximately 8% (wet basis), comparative analysis showed that a moisture content 10–11% produced the best results considering the tradeoff between the foaming and expansion temperature. This was due to the high expansion index and an expansion temperature that was sufficiently lower than the onset temperature for pellet scorching, which provides an operating window to maximize expansion and minimize the likelihood of burning.Dielectric measurements during microwave heating in short on/off cycles prior to pellet expansion suggested that the water was not as dielectrically bound for high moisture content pellets.

A rapid and non-destructive method based in time domain reflectometry analysis (TDR), which detects and quantifies the water content in the muscle, was developed for the control of abusive water addition to octopus. Common octopus samples were immersed in freshwater for different periods (0.5&ndash:32 h) to give a wide range of moisture contents, representing different commercial conditions. Control and water-added octopus were analyzed with a TDR sensor, and data correlated with moisture content were used for calibration and method validation. A maximum limit of moisture content of 85.2 g/100 g in octopus is proposed for conformity assessment, unless the label indicates that water (&gt:5%) was added. Calibration results showed that TDR analysis can discriminate control and water-added octopus, especially for octopus immersed for longer periods (32 h). In addition, moisture content can be quantified in octopus using only TDR analysis (between 80 and 90 g/100 g: RMSE = 1.1%). TDR data and correlation with moisture content show that this non-destructive methodology can be used by the industry and quality control inspections for assessment of octopus quality and to verify compliance with legislation, promoting fair trade practices, and further contributing to a sustainable use of resources.