Dielectric properties of edible oils and fatty acids as a function of frequency, temperature, moisture and composition

Modeling of Dielectric and Thermal Properties of Protein-Enriched Instant Noodles as a Function of Food Chemical Composition

Dielectric property measurement instruments are expensive and not readily available. Hence, models of the dielectric and thermal properties of protein-enriched instant noodles (PEIN) were developed as a function of the product moisture, protein, ash, fat, carbohydrate, and crude fiber contents. The chicken meat, egg yolk, and seaweed in PEIN varied from 0 to 30, 0 to 15, and 0 to 6 g/100 g flour, respectively. Results revealed that protein, fat, and ash contents of PEIN increased by chicken meat, egg yolk, and seaweed supplementation. Regression equations indicated that the moisture and protein contents significantly (P ≤ 0.05) increased, while the fat content decreased the dielectric and thermal properties. The R2 values of the dielectric constant and loss factor, thermal conductivity, and specific heat equations were 0.75, 0.87, 0.78, and 0.98, respectively. Finally, no significant differences (P > 0.05) between the properties values predicted from the model equations and the experimental data (not included in the development of model equations) was observed which indicated a good model fit.

Frequency, moisture content, and temperature dependent dielectric properties of potato starch related to drying with radio-frequency/microwave energy

To develop advanced drying methods using radio-frequency (RF) or microwave (MW) energy, dielectric properties of potato starch were determined using an open-ended coaxial-line probe and network analyzer at frequencies between 20 and 4,500 MHz, moisture contents between 15.1% and 43.1% wet basis (w.b.), and temperatures between 25 and 75 °C. The results showed that both dielectric constant (ε') and loss factor (ε″) were dependent on frequency, moisture content, and temperature. ε' decreased with increasing frequency at a given moisture content or temperature. At low moisture contents (≤25.4% w.b.) or low temperatures (≤45 °C), ε″ increased with increasing frequency. However, ε″ changed from decrease to increase with increasing frequency at high moisture contents or temperatures. At low temperatures (25-35 °C), both ε' and ε″ increased with increasing moisture content. At low moisture contents (15.1-19.5% w.b.), they increased with increasing temperature. The change trends of ε' and ε″ were different and dependent on temperature and moisture content at their high levels. The penetration depth (d _p ) decreased with increasing frequency. RF treatments may provide potential large-scale industrial drying application for potato starch. This research offers useful information on dielectric properties of potato starch related to drying with electromagnetic energy.

Microwave processing: Effects and impacts on food components

As an efficient heating method, microwave processing has attracted attention both in academic research and industry. However, the mechanism of dielectric heating is quite distinct from that of the traditional conduction heating, and is widely applied as polar molecules and charged ions interaction with the alternative electromagnetic fields, resulting in fast and volumetric heating through their friction losses. Such a heating pattern would cause a certain change in microwave treatment, which is an unarguable reality. In this review, we made a retrospect of the essential knowledge about dielectric properties and summarized the concept of microwave heating, and the impact of microwave application on the main components of foods and agricultural products, which are classified as carbohydrates, lipids, proteins, chromatic/flavor substances, and vitamins. Finally, we offered a way to resolve the drawbacks of relevant microwave treatment and outlined the directions for future research.

Novel technologies for monitoring the in-line quality of virgin olive oil during manufacturing and storage

The quality of virgin olive oil is related to the agronomic conditions of the olive fruits and the process variables of the production process. Nowadays, food markets demand better products in terms of safety, health and organoleptic properties with competitive prices. Innovative techniques for process control, inspection and classification have been developed in order to to achieve these requirements. This paper presents a review of the most significant sensing technologies which are increasingly used in the olive oil industry to supervise and control the virgin olive oil production process. Throughout the present work, the main research studies in the literature that employ non-invasive technologies such as infrared spectroscopy, computer vision, machine olfaction technology, electronic tongues and dielectric spectroscopy are analysed and their main results and conclusions are presented. These technologies are used on olive fruit, olive slurry and olive oil to determine parameters such as acidity, peroxide indexes, ripening indexes, organoleptic properties and minor components, among others. © 2016 Society of Chemical Industry.

Relaxation dynamics and thermophysical properties of vegetable oils using time-domain reflectometry

Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10 MHz to 7 GHz in the temperature region 25 to 10 °C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε ₀), high-frequency limiting static permittivity (ε _∞), average relaxation time (τ ₀), and thermodynamic parameters such as free energy (∆F _τ), enthalpy (∆H _τ), and entropy of activation (∆S _τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.

Dielectric Spectroscopy in Biomaterials: Agrophysics

Being dependent on temperature and frequency, dielectric properties are related to various types of food. Predicting multiple physical characteristics of agri-food products has been the main objective of non-destructive assessment possibilities executed in many studies on horticultural products and food materials. This review manipulates the basic fundamentals of dielectric properties with their concepts and principles. The different factors affecting the behavior of dielectric properties have been dissected, and applications executed on different products seeking the characterization of a diversity of chemical and physical properties are all pointed out and referenced with their conclusions. Throughout the review, a detailed description of the various adopted measurement techniques and the mostly popular equipment are presented. This compiled review serves in coming out with an updated reference for the dielectric properties of spectroscopy that are applied in the agrophysics field.

Effects of cytoplasm and reactant polarities on acid-catalyzed lipid transesterification in wet microalgal cells subjected to microwave irradiation

The polarities of the cytoplasm and reactants were measured through dielectric spectroscopy, contact angle test, NMR, and FTIR to investigate the mechanisms underlying acid-catalyzed lipid transesterification in wet microalgal cells subjected to microwave irradiation. Organics with apolar functional groups in the cytoplasm decreased the contact angle of methanol against triglyceride by 13.92°, which subsequently increased transesterification efficiency by 2.4 times. The microalgal biomass, given its higher hydrophilicity index of 1.96 than lipids, was more accessible to hydrophilic alcohols, which subsequently promoted transesterification. Water in the cytoplasm promoted the dielectric constant of methanol and increased the contact angle of methanol against triglyceride by 20.51°, which subsequently decreased transesterification efficiency by 72.6%. The inhibitory effect of water on transesterification weakened with the prolonged carbon lengths of the alcohols because of decreased polarity. Microwave decreased the electric constants of alcohols and reduced the polarity difference between alcohols and lipids, thereby improving transesterification efficiency.

Thermal, Structural, and Physical Properties of Freeze Dried Tropical Fruit Powder

This study evaluates the physical properties of freeze dried tropical (guava, sapota, and papaya) fruit powders. Thermal stability and weight loss were evaluated using TGA-DSC and IR, which showed pectin as the main solid constituent. LCR meter measured electrical conductivity, dielectric constant, and dielectric loss factor. Functional groups assessed by FTIR showed presence of chlorides, and O–H and N–H bonds in guava, chloride and C–H bond in papaya, and chlorides, and C=O and C–H bonds in sapota. Particle size and type of starch were evaluated by X-ray diffraction and microstructure through scanning electronic microscopy. A semicrystalline profile and average particle size of the fruit powders were evidenced by X-ray diffraction and lamellar/spherical morphologies by SEM. Presence of A-type starch was observed in all three fruits. Dependence of electric and dielectric properties on frequency and temperature was observed.

Electrochemical impedance spectroscopy as an alternative to determine dielectric constant of potatoes at various moisture contents

The dielectric (DE) properties, specifically the DE constant (ε') and loss factor (ε''), were measured for vacuum-dried and freeze-dried potato samples at a microwave frequency of 2.45 GHz over a range of different moisture contents (MCs) using a DE probe and also a 2-probe electrochemical impedance spectroscopy (EIS). Third-order polynomial models (ε' = f₁(MC); and ε'' = f₂(MC)) at room temperature were developed for regression analysis. Additionally, at various temperatures (T), biphasic 3rd-order polynomial models (ε' = f₁(MC, T); and ε'' = f₂(MC, T)) were obtained to determine ε' and ε'' as a function of MC and T using measured data. The vacuum-dried potato sample showed a good fitness of ε' and ε'' (R² = 0.95 and 0.96, respectively) to the regression model with the range of MCs from 18% to 80% (w/w), while the freeze-dried potato sample showed a good fitness of ε' and ε'' to the 1st-phase regression model with MC < 50% w/w (R² = 0.95 and 0.96, respectively) and the 2nd-phase regression model with MC > 50% w/w (R² = 0.94 to 0.96). EIS measurements were also used to obtain correlation impedances for ε' and ε'' determined by the DE probe method. The resulted regression analysis meets the demands for simple, rapid, and accurate assessment for transient values of ε' and ε'' of food products during dehydration/drying processes. The EIS method was verified to be a successful alternative to direct measurements of ε' and ε''.

Correlation of basic oil quality indices and electrical properties of model vegetable oil systems

Model vegetable oil mixtures with significantly different basic oil quality indices (free fatty acid, iodine, and Totox values) were prepared by adding oleic acids, synthetic saturated triglycerides, or oxidized safflower oil ( Carthamus tinctorius ) to the oleic type of sunflower oil. Dielectric constants, dielectric loss factors, quality factors, and electrical conductivities of model lipids were determined at frequencies from 50 Hz to 2 MHz and at temperatures from 293.15 to 323.15 K. The dependence of these dielectric parameters on basic oil quality indices was investigated. Adding oleic acids to sunflower oil resulted in lower dielectric constants and conductivities and higher quality factors. Reduced iodine values resulted in increased dielectric constants and quality factors and decreased conductivities. Higher Totox values resulted in higher dielectric constants and conductivities at high frequencies and lower quality factors. Dielectric constants decreased linearly with temperature, whereas conductivities followed the Arrhenius law.

Rapid screening of fatty acid alkyl esters in olive oils by time domain reflectometry

The main aim of the present research is to assess the possibility of quickly screening fatty acid alkyl esters (FAAE) in olive oils using time domain reflectometry (TDR) and partial least-squares (PLS) multivariate statistical analysis. Eighteen virgin olive oil samples with fatty acid alkyl ester contents and fatty acid ethyl ester/methyl ester ratios (FAEE/FAME) ranging from 3 to 100 mg kg(-1) and from 0.3 to 2.6, respectively, were submitted to tests with time domain resolution of 1 ps. The results obtained in test set validation demonstrated that this new and fast analytical approach is able to predict FAME, FAEE, and FAME + FAEE contents with R(2) values of 0.905, 0.923, and 0.927, respectively. Further measurements on mixtures between olive oil and FAAE standards confirmed that the prediction is based on a direct influence of fatty acid alkyl esters on the TDR signal. The suggested technique appeared potentially suitable for monitoring one of the most important quality attribute of the olive oil in the extraction process.

Investigation of microwave dielectric properties of biodiesel components

Advanced microwave technology has the potential to significantly enhance the biodiesel production process. Knowledge of dielectric properties of materials plays a major role in microwave design for any process. Dielectric properties (ε' and ε") of biodiesel precursors: soybean oil, alcohols and catalyst and their different mixtures were measured using a vector network analyzer and a slim probe in an open ended coaxial probe method at four different temperatures (30, 45, 60 and 75 °C) and in the frequency range of 280 MHz to 4.5 GHz. Results indicate that the microwave dielectric properties depend significantly on both temperature and frequency. Addition of catalyst significantly affected the dielectric properties. Dielectric properties behaved differently when oil, alcohol and catalyst was mixed at room temperature before heating and when the oil and the alcohol catalyst mixture was heated separately to a pre-determined temperature before mixing. These results can be used in designing microwave based transesterification system.

Biomarker-free dielectrophoretic sorting of differentiating myoblast multipotent progenitor cells and their membrane analysis by Raman spectroscopy

Myoblasts are muscle derived mesenchymal stem cell progenitors that have great potential for use in regenerative medicine, especially for cardiomyogenesis grafts and intracardiac cell transplantation. To utilise such cells for pre-clinical and clinical applications, and especially for personalized medicine, it is essential to generate a synchronised, homogenous, population of cells that display phenotypic and genotypic homogeneity within a population of cells. We demonstrate that the biomarker-free technique of dielectrophoresis (DEP) can be used to discriminate cells between stages of differentiation in the C2C12 myoblast multipotent mouse model. Terminally differentiated myotubes were separated from C2C12 myoblasts to better than 96% purity, a result validated by flow cytometry and Western blotting. To determine the extent to which cell membrane capacitance, rather than cell size, determined the DEP response of a cell, C2C12 myoblasts were co-cultured with GFP-expressing MRC-5 fibroblasts of comparable size distributions (mean diameter ∼10 μm). A DEP sorting efficiency greater than 98% was achieved for these two cell types, a result concluded to arise from the fibroblasts possessing a larger membrane capacitance than the myoblasts. It is currently assumed that differences in membrane capacitance primarily reflect differences in the extent of folding or surface features of the membrane. However, our finding by Raman spectroscopy that the fibroblast membranes contained a smaller proportion of saturated lipids than those of the myoblasts suggests that the membrane chemistry should also be taken into account.

Organogel-emulsions with mixtures of β-sitosterol and γ-oryzanol: influence of water activity and type of oil phase on gelling capability

In this study, water-in-oil emulsions were prepared from water containing different salt concentrations dispersed in an oil phase containing a mixture of β-sitosterol and γ-oryzanol. In pure oil, the β-sitosterol and γ-oryzanol molecules self-assemble into tubular microstructures to produce a firm organogel. However, in the emulsion, the water molecules bind to the β-sitosterol molecules, forming monohydrate crystals that hinder the formation of the tubules and resulting in a weaker emulsion-gel. Addition of salt to the water phase decreases the water activity, thereby suppressing the formation of sitosterol monohydrate crystals even after prolonged storage times (∼1 year). When the emulsions were prepared with less polar oils, the tubular microstructure was promoted, which significantly increased the firmness of the emulsion-gel. The main conclusion of this study is that the formation of oryzanol and sitosterol tubular microstructure in the emulsion can be promoted by reducing the water activity and/or by using oils of low polarity.

Measurement techniques and application of electrical properties for nondestructive quality evaluation of foods-a review

Non-destructive systems are recent trends for quality evaluation of fruits and vegetables. Information on post-harvest variations in electrical properties is needed to develop new instruments for this purpose. Electrical properties are finding increasing application in agriculture and food processing industries. Knowledge of dielectric properties of foods as a function of moisture content and temperature is essential in the design and control of drying systems. As simple, rapid and non-destructive measuring techniques, dielectric spectroscopy provides information about the dielectric response of materials to electromagnetic field. Electrical properties of agricultural materials have been of interest for many years. The interest in dielectric properties of materials has historically been associated with the design of electrical equipment. This review paper covers theoretical aspects of different electrical properties, their measurement techniques, applications of dielectric properties in agriculture/food processing sector and potential applications of thermal imaging (TI) for quality and safety assessment in food processing. The values of dielectric properties of a number of products including food grains, fruits and vegetables, and meat and meat products are presented in table form. This comprehensive coverage will be useful for academic, scientific and industrial community in treating and applying the facts in developing/testing new processes and products based on electromagnetic energy application.

Non-invasive determination of plant biomass with microwave resonators

Non-invasive and rapid determination of plant biomass would be beneficial for a number of research aims. Here, we present a novel device to non-invasively determine plant water content as a proxy for plant biomass. It is based on changes of dielectric properties inside a microwave cavity resonator induced by inserted plant material. The water content of inserted shoots leads to a discrete shift in the centre frequency of the resonator. Calibration measurements with pure water showed good spatial homogeneity in the detection volume of the microwave resonators and clear correlations between water content and centre frequency shift. For cut tomato and tobacco shoots, linear correlations between fresh weight and centre frequency shift were established. These correlations were used to continuously monitor diel growth patterns of intact plants and to determine biomass increase over several days. Interferences from soil and root water were excluded by shielding pots with copper. The presented proof of principle shows that microwave resonators are promising tools to quantitatively detect the water content of plants and to determine plant biomass. As the method is non-invasive, integrative and fast, it provides the opportunity for detailed, dynamic analyses of plant growth, water status and phenotype.