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Dielectric constant ( 3 0 ) and loss factor ( 3 00 ) of raisins, 15 g/100 g w.b. ( ), dates, 19.7 g/100 g w.b. ( ), apricots, 24.6 g/100 g w.b. ( ), figs, 27.3 g/100 g w.b. ( ), and prunes, 30.2 g/100 g w.b. ( ) as a function of frequency at 20 C.
Source publication
Phytosanitary/quarantine regulations for many countries require that certain dried fruit be disinfected prior to export; however, current technologies involve the use of toxic chemicals and conventional thermal methods are either undesirable or cause loss of volatile components, browning and texture change. Newer physical methods including dielectr...
Contexts in source publication
Context 1
... Frequency-dependent dielectric property A summary of dielectric properties for the dried fruits is provided in Table 2 and a graphic depiction of dielectric constants and the loss factors at 20 C is shown in Fig. 2. The dielectric properties for these five dried fruits demonstrated a similar trend: they decreased with increasing frequency. However, differences in the values of dielectric properties of the tested samples at specific frequencies and temperatures were observed. Prunes had the highest dielectric constant and loss factor values among ...
Context 2
... Frequency-dependent dielectric property A summary of dielectric properties for the dried fruits is provided in Table 2 and a graphic depiction of dielectric constants and the loss factors at 20 C is shown in Fig. 2. The dielectric properties for these five dried fruits demonstrated a similar trend: they decreased with increasing frequency. However, differences in the values of dielectric properties of the tested samples at specific frequencies and temperatures were observed. Prunes had the highest dielectric constant and loss factor values among ...
Citations
... Some factors that affect the process's uniformity are the product's size and shape and the position between the electrodes. Several attempts have been made to improve the uniformity of the process, such as the rotation of the product or using a conveyor system to move the product inside the equipment, water immersion of the product, stirring/mixing, hot water preheating, hot air assistance, changes in the composition of the product, changes in electrode shapes, and adding some dielectric material to the product, among others [9,14,49,[54][55][56][57][58]. Hao et al. [54] tested using a rotation device with sample mixing during RF heating of some granular products. ...
Radio frequency (RF) is a novel technology with several food processing and preservation applications. It is based on the volumetric heating generated from the product’s dielectric properties. The dielectric properties of each material are unique and a function of several factors (i.e., temperature, moisture content). This review presents a list of dielectric properties of several foods and describes the use of RF as an innovative technology for the food industry. This paper includes several examples of pasteurization, fungi inactivation, and disinfestation in selected food products. The aim of this review is to present the potential applications of RF in pasteurization and disinfestation and research needs that should be addressed. RF has been successfully applied in the inactivation of pathogens such as Salmonella spp., Listeria monocytogenes, and Escherichia coli in low- and high-moisture food. The disinfestation of crops is possible using RF because of selective heating. This process inactivates the insects first because of the different dielectric properties between the pests and the food. The products’ final quality can be considerably better than conventional thermal processes. The processing time is reduced compared to traditional heating, and thermal damage to the food is minimized. The main drawback of the technology is the lack of uniform heating, mainly when the product is surrounded by a packaging material with different dielectric properties from the food.
... Postbaking application of biscuits, crackers, or breakfast cereals has been fully commercialized since the 1960s by the biscuit industry for benefits in the removal of water from the high-moisture center zone of the product. Radiofrequency technology is also used for defrosting operations in products such as fish, meat, and other raw or processed food materials (Alfaifi et al., 2013;Awuah et al., 2014;Ha et al., 2013). Strayfield (UK), STALAM (Italy), Thermex-Thermatron (USA) or Radio-Frequency Company (USA) are some suppliers that offers radio frequency equipment for food commercial applications (Awuah et al., 2014). ...
Emerging thermal processes for food have been explored, implemented, and introduced in recent decades as an alternative to conventional heating methods. Emerging thermal technologies could shorten processing times and provide savings in terms of energy and water consumption in different food products of liquid or solid form. In this chapter, potential opportunities in processes such as pasteurization, sterilization, blanching, cooking, drying, thawing, or baking have been reviewed with the application of infrared heating, radio frequency heating, microwave heating, Ohmic heating, and even with the combination of technologies based on recent publications and current industrial implementations.
... The lowest penetration depth was 0.189 m for ground kernels with 21% MC at 27.12 MHz and 90 °C. The similar effects of frequency, temperature, and MC were reported for nuts, dried fruit, and vegetables, and milk powders (Alfaifi et al., 2013;Dag et al., 2019;Gao et al., 2012;Ozturk et al., 2016). ...
Hot air–assisted radio frequency (HARF) heating was used to dry and blanch inshell hazelnuts with high (19%) and low (11%) moisture content (MC) simultaneously. The effects of target temperature (70, 80, and 90 °C) and holding time (0 or 5 min at target temperature) on heating uniformity and inactivation of polyphenol oxidase (PPO) and peroxidase (POD) were investigated. The dielectric properties and penetration depth of the ground kernels, shells, and inshell hazelnuts were measured at 3 MCs (6–22%), 2 frequencies (13.56 and 27.12 MHz), and 7 temperatures (25–95 °C). Hazelnut kernels showed higher dielectric constant and loss factor than shells and inshell hazelnuts. Target temperature did not affect heating uniformity for inshell hazelnuts. A 5-min holding time at the target temperature resulted in better heating uniformity and lower POD and PPO activities (27–35% and 40–45% reduction, respectively). This study demonstrated the feasibility of simultaneous rapid drying and blanching of inshell hazelnuts using HARF technology.
... Experts analyze the images captured by the capsule endoscopes, and they conclude the health condition of an individual's gastrointestinal passage. The capsule endoscopes follow the peristaltic movement and lack location, direction, and speed control in the gastrointestinal tract, leading to incorrect diagnosis (Alfaifi et al., 2013). Several clinical trials show that capsule endoscopy aids in precisely diagnosing obscure bleeding in the gastrointestinal tract, small intestine neoplasm, Crohn's disease, and patients with familial adenomatous polyposis syndromes (Ozturk et al., 2016). ...
Edible electronics presuppose the utilization of food ingredients to build various components of a fully functional sensor that can be consumed orally. The sensors stay inside the body for a particular time either to monitor physiological functions or treat diseases then transmit the information to a connected mobile phone. However, not all food components satisfy the criteria required for constructing a consumable sensor. Therefore, it is essential to thoroughly analyze the components before implementation. The chapter reviews the characteristics of food-based electrical components employed in the fabrication of edible electronics and their consumer acceptance. The authors aspire to deliver an overview of the recent advances and reveal the relationship between food and electronics. The future of edible electronics may be linked to imparting nutrients at the desired site along with improving the bioavailability of the ingested nutrients. This automation has an appreciable potential to completely reshape the research areas in both food and medical sciences in the future.
... Industrial-scale RF treatments for insect control in walnuts have been developed, and results showed that the average energy efficiency of two RF units in series could reach 79.5% when heating walnuts at 1561.7 kg h −1 (Wang et al. 2007a,b). According to the DPs of raisins, dates, apricots, figs, and prunes marsured by Alfaifi et al. (2013), differential heating for postharvest insect pest control is possible since the dielectric constant and loss factor of the tested dried fruits is lower than those of pests. Alfaifi et al. (2014) established a computer model to investigate the RF heating uniformity of raisins packed in a rectangular plastic container, corners, and edges were heated more than the centers in each layer of the RF-treated raisins. ...
In the last two decades, new preservation technologies have drawn the attention of food producers, who wish to satisfy the consumers' increasing demand for fresh-like food products free or with low amounts of chemical additives and processed without the need for severe heating. Among these procedures, short-wavelength ultraviolet light (UV-C, 254 nm) is a low-cost technology, which does not leave any residue and effectively inactivates microorganisms with low or negligible damage to food quality. However, used alone, its use is limited to the treatment of surfaces or clear liquid foods in which UV-C photons can easily reach microbial cells. Its effectiveness can be significantly affected by the optical and physical characteristics of the treated media, thus hindering the disinfection process. Hence, the use of UV-C light under a hurdle approach, which considers its combination with other stressors, could be an interesting alternative to maximize its benefits in terms of microbial reduction and food quality. In this chapter, an attempt to streamline the information available on key aspects of current UV-based strategies in various foods and beverages is presented. On balance, significant progress has been made in this regard, which opens an ever-widening range of possibilities for the future industrial adoption of some of these strategies for food preservation purposes. The uses, drawbacks, effects, mechanism, and short-term goals of the UV-C-based technologies are discussed in this chapter.
... where c is the speed of light in vacuum (3 × 10 8 m/s). Contrary to the trend in heating rate, the penetration depth decreases with increasing frequency and temperature based on Equation (3) (Alfaifi et al. 2013). The findings of revealed that the heating uniformity was improved as the frequency declined from 40.68 to 6.78 MHz when subjected to RF drying and also supported the above results. ...
Radio frequency (RF) drying is an emerging technology for food and agricultural products, holding features of rapid, uniform, stable, and volumetric heating, high energy efficiency, and moisture leveling. However, the RF drying with a single stage commonly has drawbacks of unexpected product quality, non-uniform moisture distribution, and prolonged drying time. The multi-stage drying approach could overcome the shortcomings of one-stage strategy accordingly by applying different drying methods or operating parameter values in each phase separately. This review describes the principle of RF heating, presents the typical systems and superiorities of RF drying, and provides a comprehensive overview on recent development in applications of both the one-stage and the multi-stage RF drying, and analysis of drying characteristics and merits for different types of the two-stage strategy. This review finally proposes recommendations for future studies in improving and optimizing the existing RF drying protocols and scaling up them to industrial applications.
... Dielectric properties are utilized in fruit drying processes if DH is applied Drying process are often accomplished in a short time, and provides more qualified dried products with low energy requirement [55]. Radiofrequency and DH also protect food materials from insects that already present in dried fruits [56]. Dielectric application is often utilized in pasteurization, sterilization, tempering of concentration of liquid foods like fruit juices. ...
Dielectric properties of foods are used to explain interactions of foods with electric fields. It determines the interaction of electromagnetic waves with matter and defines the charge density under an electric field. For engineering point of view, dielectric properties are the foremost important physical properties related to radio frequency and microwave heating, it is critical to possess knowledge of the dielectric properties of materials in products and process development and, within the modern design of dielectric heating system for the need of desired process. Dielectric properties are often categorized into two: dielectric constant and dielectric loss factor. Dielectric constant is the ability of a material to store microwave energy and dielectric loss factor is the ability of a material to dissipate microwave energy into heat. Dielectric properties of food materials are required for various applications in food industry like microwave (at 915 or 2450 MHz), radio wave (at 13.56, 27.12 or 40.68 MHz) and magnetic field processing. In this review, the dielectric properties of various food groups were listed such as; Cereal grains and oilseeds, Bakery product, Dairy products, Poultry products, Fruits and vegetables. Dielectric properties are utilized in fruit drying processes, protect food materials from insects that already present in dried fruits, pasteurization, sterilization, tempering of concentration of liquid foods such as fruit juices, identification, processing, quality monitoring of fats and oils and improvement during oil processing and storage. The dielectric studies of food materials are an important tool to identify the quality of food materials and to improve dielectric heating uniformity. Frequency, moisture content, phase change, storage time and temperature are main factors that influence the dielectric properties of food material.
... From the Eq.1 the absorption of microwave energy is proportional to the dielectric constant and dielectric loss factor of the materials. The dielectric properties of the materials depend on the frequency of the applied electric field and the temperature of the material [10].Dielectric properties of a material consist of dielectric constant, this value is a measure of the ability of the material to store electromagnetic energy, and dielectric loss factor is a measure of the ability to dissipate electrical energy into heat. Expressed by the following equation [11] = ' -j " (2) where dielectric properties ' … dielectric constant (real component) J = (-1) 0.5 " … dielectric loss ...
... Increasing temperature results increasing dielectric constant and loss factor for each frequency. The loss factor of all dried fruit samples increased with increasing moisture content (Alfaifi et al., 2013). Dielectric properties are also used in drying processes and insect control of agricultural products. ...
Dielectric properties of materials are used for evaluating their interactions with electromagnetic energy. Dielectric properties of food materials are required for various applications in food industry such as microwave (at 915 or 2450 MHz), radio wave (at 13.56, 27.12 or 40.68 MHz) and magnetic field processing. In order to understand the response of food materials to electromagnetic energy, dielectric parameters must be determined as a function of frequency, temperature, composition and moisture content. In this review, the dielectric properties of different food groups were listed depending on temperature and frequency ranges. In addition to the literature data of dielectric properties, the penetration depths of microwave or radio wave through food groups were calculated. The effects of temperature and composition (mostly moisture content) on dielectric properties depend on the type of the food and sometimes on frequency. However, the effect of frequency is constant; increased frequency decreased dielectric constant, loss factor and penetration depth. The lowest calculated penetration depth belonged to the fish surimi gel as 3.39 mm at microwave frequency whereas they were high generally for fats, oily seeds and flours (max was 372602 mm for corn flour). It appears that dielectric properties of foods should be investigated further depending on the interactions between frequency, temperature and composition. And then, dielectric heating based on the aim of the process can be applied accordingly. Besides, it appears that the moisture content and especially the dipole rotation and the conductivity movements of the molecules in free water content of the food are some of the most critical factors influencing the dielectric properties of food materials.
... The dielectric properties of most materials depend on the frequency of the applied alternating electric field, density, composition, and structure of the material (Venkatesh and Raghavan 2004). These studies and applications of these properties have been performed in eggs, grains, fruits, vegetables, juice and wine, baked foods and flours, dairy products, fish, and meat products (Alfaifi et al. 2013;Kudra et al. 2016;Nunes et al. 2006;Tanaka et al. 2005;Zhu et al. 2015). Additionally, dielectric properties and fatty acids have been investigated as functions of frequency and composition, and the dielectric constants of the oils have shown remarkable differences among types of oils (Hu et al. 2008). ...
To develop a new and rapid qualitative and quantitative analysis of flaxseed oil adulteration with different vegetable oils, we investigated the dielectric spectroscopy coupled with multivariate methodology in the frequency range between 10 and 3000 MHz. Linear discriminant analysis was used to distinguish flaxseed oil from other adulterants based on dielectric spectra, and the oil samples were easily grouped in different clusters. The partial least square model was developed for the quantification of the sample adulteration percentage independent from the adulterating oil, which showed a good prediction capability for the adulterant concentrations. The calibration provided a correlation coefficient (R-value) of 0.9961, and the blind sample validation indicated that the R-value of the validation and precision analyses was close to 1. Analysis was characterized as having good precision by slightly low relative standard deviation. Thus, dielectric spectroscopy could be effectively used to discriminate adulterated flaxseed oil from different types of oils at 2% levels.
