Dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying and correlation with the water state

Abstract

The dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying were determined, by using a network analyzer and an open-ended coaxial-line probe at microwave frequency (915 and 2450?MHz). The permittivity at 25?°C was also correlated to the water state determined by low field nuclear magnetic resonance (LF-NMR) analysis. Results showed that the dielectric constant ε' and loss factor ε″ of A. bisporus slices were affected significantly by the composition of water state in the sample. Thermosonic pretreatment enhanced the influence of semi-bound water (M₂₂) and bound water (M₂₁) on the permittivities in sample slices during microwave vacuum drying (MVD). The dependency of permittivities on the moisture content and temperature at 915 and 2450?MHz for thermosonically treated A. bisporus samples could be described by third-degree polynomial models, with R² higher than 0.998. Infrared thermal imaging analysis confirmed that thermosonic pretreatment is a potential technology to promote the uniformity of A. bisporus slices during the MVD process.     

Study of the drying process of ginger (Zingiber officinale Roscoe) slices in microwave fluidized bed dryer

ABSTRACT

To research about the temperature and moisture characteristics of ginger slices in microwave fluidized bed drying (MFD), some microwave drying experiments in different powers and hot-air drying experiment were used, and the drying quality and moisture drying curves were studied in contrast, finding MFD with advantages such as good quality and high efficiency. In order to understand the water flow characteristics of ginger slices in MFD, low nuclear magnetic resonance was used to detect the materials in different drying stages, and it was found that free water (FW), immobilized water (IW), and bond water (BW) could be converted to the other forms, especially the form that combined with the dry matter is much firmer. FW is the main water state in fresh ginger slices and converts to the IW quickly in the beginning stage, and then both FW and IW decreased until the final stage is reached. Finally, the content of BW increased, and the material can be stored safely. Gingerol is the main flavor component of ginger, and it was detected through LC-20A high-performance liquid chromatography; it was found that the content of 6-gingerol, 8-gingerol, and 10-gingerol increased in various drying processes, especially 10-gingerol that has a positive role to protect the taste of the ginger.     

Influence of blanching treatment and drying methods on the drying characteristics and quality changes of dried sardine (Sardinella gibbosa) during storage

The aim of this study is to examine the drying characteristics of blanched and unblanched sardine during indoor and open sun drying processes. Changes in temperature and relative humidity of the air during drying were recorded. The color, peroxide value (PV), thiobarbituric acid reactive substances (TBARS), free fatty acid (FFA) content, fatty acid composition, and sensory attributes of dried samples were also evaluated once a month for 5 months of storage. High drying rates were obtained in all samples at the start of drying and then decreased with increasing drying time. The highest drying rate and effective water diffusivity (D_eff) were observed in blanched sardine during open sun drying. Blanching treatment slowed down the FFA progression during product storage but adversely affected the color, PV, and TBARS content as well as sensory properties. Although sardine dried for a longer time under indoor drying conditions, it attained a stable moisture ratio that was lower than in open sun-dried samples. Indoor drying produced a quality stable product with less lipid oxidation and the desired moisture content, higher polyunsaturated fatty acids and sensory properties. Blanching treatment negatively affected the fish quality and is therefore not recommended for commercial sardine drying.     

Influence of postharvest drying conditions on resistant starch content and quality of non-waxy long-grain rice (Oryza sativa L.)

This study investigated the effect of postharvest drying conditions on resistant starch (RS) content and quality of rice. Paddy was subjected to hot-air drying at 40, 65, 90, and 115°C, and sun drying. Drying conditions altered head rice yield, RS and overall firmness of cooked rice, and some pasting properties of rice flour. No significant variation in RS of uncooked rice and surface firmness of cooked rice was observed among the samples. However, RS of cooked rice from sun drying was lower than the others. Higher temperature in hot-air drying resulted in a slightly increase in RS of cooked rice.     

Spray and freeze drying of human milk on the retention of immunoglobulins (IgA,IgG, IgM)

Several freeze-drying and spray-drying methods were investigated in relation to the retention of immunoglobulins (Ig) A, IgG, and IgM. Spray drying produced human milk powders with 2% humidity and a good retention of IgG (>88%) and IgM (～70%). However, only 38% of IgA remained after spray drying. For freeze drying, only the highest heating plate temperature used in this study (40°C) brought IgA content down to 55% in powder with 1.75% residual humidity, whereas milk samples undergoing lower temperatures had higher preservation rates (75% for IgA and 80% for IgG and IgM) and higher residual moisture contents. From these results, it can be concluded that IgA is the most sensitive Ig lost during drying processing of human milk. The best method to generate human milk powders without a significant loss of Ig was thus freeze drying at 30°C heating plate temperature, which accelerated the process compared to lower processing temperatures, but still had good overall Ig retention.     

Effect of carbonic maceration pre-treatment on the drying behavior and physicochemical compositions of sweet potato dried with intermittent or continuous microwave

Drying behavior and change of physicochemical compositions of sweet potato in intermittent microwave drying (IMD) and continuous microwave drying (CMD) combined with or without carbonic maceration (CM) pre-treatment were investigated. A quantity of 100?g of fresh or CM pre-treated samples were dried in IMD at 700?W with power on–off ratio of 1/6 (5?s/30?s, t_on/t_off) or dried in CMD with power density of 1?W/g. The results indicated that the process of CM?+?IMD as compared with IMD, CMD, and CM?+?CMD had the shortest drying time, the lowest activation energy (E_a), and the biggest effective moisture diffusivity (D_eff) and exhibited the highest total content of phenols, anthocyanins, flavonoids, β-carotene, ascorbic acid retention rate, as well as scavenging free radical capability 2,2-diphenyl-1-picrylhydracyl of dried product. Meanwhile, color measurements indicated that CM?+?IMD could get the most desirable color of dried sweet potatoes. Therefore, CM pre-treatment is promising for industrial application.     

Influence of the aging time of yttria stabilized zirconia slips on the cracking behavior during drying and green properties of cast tapes

Tape-casting process was used to produce yttria stabilized zirconia (YSZ) substrates in an aqueous system using a low amount of an acrylic latex binder. Concentrated suspensions with different aging times were cast, and the influence of the slip aging time on the drying kinetics and cracking behavior of the tapes were studied. In addition, the effect of the slip aging time on the properties of the resultant green tapes was investigated. The latex particles consolidated by coalescence during the aging time of the slips and resulted in an increase in the smaller pore size of the cast tapes. The pore radius increased with increasing the slip aging time up to 14 days thereby decreasing the capillary pressure in the liquid. Aging times over 14 days did not change the pore radius and consequently the capillary pressure. The capillary tension drove the consolidation; the tapes produced from slips with lower aging times which had higher capillary pressure shrank more, had lower pore volume and consequently higher green density. Cracking was found in tapes prepared from slips with aging times shorter than 14 days; the crack area decreased with increasing the slip aging time. For slip aging time ≥14 days cracking was not observed. Aging before casting up to 14 days reduced cracking in tapes prepared with low amounts of latex; however, the lower capillary pressure resulted in low green density of the cast tapes.     

Effects of three conventional drying methods on the lipid oxidation,fatty acids composition,and antioxidant activities of walnut (Juglans regia L.)

Three walnut (Juglans regia L.) drying methods (sun drying, direct oven drying, and intermittent oven drying) were employed, and the consequent changes in lipid oxidation attributes, such as acid value (AV), peroxide value (POV), saponification value (SV), fatty acid composition, and antioxidant activity [including reducing power, superoxide anion scavenging activity, 1,1-diphenyl-2-picrylhydrazyl free radical scavenging activity (DPPH), lipoxygenase (LOX) activity, total phenols content (TPC), and total flavonoids content (TFC)] were investigated in this study. Sun drying resulted in the highest AV, POV, and SV, followed by direct oven drying and intermittent oven drying. Antioxidant activities and related compounds, TPC and TFC, were initially increased and then declined during drying, and a significant correlation was found between antioxidant activity and TPC and TFC. The LOX activities of all samples showed an increasing trend, although those of the sun-dried samples were the lowest. The walnuts dried with the intermittent oven drying method contained more linoleic acid than those dried by direct oven drying. Overall, intermittent oven drying appears to be a promising strategy for fresh walnut drying.     

Effect of Bi2O3 additives on sintering and microwave dielectric behavior of La(Mg0.5Ti0.5)O3 ceramics

Bi₂O₃ was selected as liquid phase sintering aid to lower the sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics. The sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics is generally high, about 1600 °C. However, the sintering temperature was significantly lowered about 275 °C from 1600 °C to 1325 °C by incorporating in 15 mol% Bi₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (?_r) value of 40.1, a quality factor (Q × f) value of 60,231 GHz, and the temperature coefficient (τ_f) value of 70.1 ppm/°C. During all addition ranges, the relative dielectric constants (?_r) were different and ranged from 32.0 to 41.9, the quality factors (Q × f) were distributed in the range of 928–60,231 GHz, and the temperature coefficient (τ_f) varies from 0.3 ppm/°C to 70.3 ppm/°C. Noticeably, a nearly zero τ_f can be found for doping 5 mol% Bi₂O₃ sintering at 1325 °C. It implies that nearly zero τ_f can be achieved by appropriately adjusting the amount of Bi₂O₃ additions and sintering temperature for La(Mg_0.5Ti_0.5)O₃ ceramics.     

Effect of Various Drying Methods on Flavor Characteristics and Physicochemical Properties of Dried Curry Leaves (Murraya koenigii L. Spreng)

Curry leaves (Murraya koenigii. L. Spreng) dried using microwave, combo (combination of microwave and convection), infrared (IR), inert gas, hot air oven, cross-flow tray, freeze drying, and the effect of drying on flavor and quality characteristics such as chlorophyll analyzed by spectrophotometry and Ca, Fe, Mg, Cu, Na, K, and Zn by atomic absorption spectrophotometry (AAS) were compared with sun and shade drying along with fresh leaves. Clevenger hydrodistillation indicated that the shade-dried leaves (1.34%) retained a higher amount of essential oil followed by microwave-dried leaves (1.06%). About 65 components were identified by gas chromatography–mass spectroscopy (GC-MS) analysis and microwave drying retained a comparatively greater number of volatiles followed by combo-, IR-, and inert gas–dried samples. β-caryophyllene, E-β-ocimene, and italicene ether were found in all of the dried samples but in variable proportions.     

Comparison of the Phenolic Content and Antioxidant Activities of Apocynum venetum L. (Luo-Bu-Ma) and Two of Its Alternative Species

The leaves of Apocynum venetum L. (AV), a native Chinese plant, have been used as folk medicine in China and Japan. This study evaluated the content of the active antioxidant component and antioxidant activities of AV, and its two alternative species, Poacynum pictum (Schrenk) Baill. (PP) and Poacynum hendersonii (Hook.f.) Woodson (PH). The total phenolic and total flavonoid contents were determined. In addition, the quantitative analysis of two major flavonoid compounds (hyperoside and isoquercitrin) was carried out by HPLC. The antioxidant activities were investigated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity method, the reducing power test and the chelating ability of ferrous ions. The highest total phenolic and flavonoid contents were observed in the AV methanolic extract, followed by the PP and PH methanolic extracts. HPLC analysis indicated that isoquercitrin was one of the major components in all three species, however, hyperoside was only detected in AV at high levels. All the antioxidant assays we performed demonstrated that the AV extract was markedly superior to those of the other two species.     

A Comparison of the Effect of Lead (Pb) on the Slow Vacuolar (SV) and Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

Little is known about the effect of lead on the activity of the vacuolar K⁺ channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl₂) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K⁺, the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl₂ was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K⁺ fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb²⁺ reduces the growth of plant cells.     

Effect of Bi2O3 and B2O3 additives on the sintering temperature, microstructure, and microwave dielectric properties for Sm(Mg0.5Ti0.5)O3 ceramics

The microwave dielectric properties of Sm(Mg_0.5Ti_0.5)O₃ incorporated with various amount of Bi₂O₃ and B₂O₃ additives have been investigated systematically. In this study, both Bi₂O₃ and B₂O₃ additives acting as a sintering aid can effectively lower the sintering temperature from 1550 °C to 1300 °C. The ionic radius of Bi³⁺ for a coordination number of 6 is 0.103 nm, whereas the ionic radius of B³⁺ is 0.027 nm. Clearly, the ionic radius of Bi³⁺ is greatly larger than one of B³⁺, which resulted in the specimens incorporated with Bi₂O₃ having larger lattice parameters and cell volume than those incorporated with B₂O₃. The experimental results show that no second phase was observed throughout the entire experiments. Depending on the interfacial tension, the liquid phase may penetrate the grain boundaries completely, in which case the grains will be separated from one another by a thin layer as shown in Sm(Mg_0.5Ti_0.5)O₃ ceramics incorporated with Bi₂O₃. Whereas, in Sm(Mg_0.5Ti_0.5)O₃ ceramics incorporated with B₂O₃, the volume fraction of liquid is high, the grains may dissolve into the liquid phase, and rapidly rearrange, in which case contact points between agglomerates will be dissolved due to their higher solubility in the liquid, leading plate-like shape microstructure.A dielectric constant (?_r) of 29.3, a high Q × f value of 26,335 GHz (at 8.84 GHz), and a τ_f of −32.5 ppm/°C can be obtained for Sm(Mg_0.5Ti_0.5)O₃ ceramics incorporated with 10 mol% Bi₂O₃ sintered at 1300 °C. While Sm(Mg_0.5Ti_0.5)O₃ ceramics incorporated with 5 mol% B₂O₃ can effectively lower temperature coefficient of resonant frequency, which value is −21.6 ppm/°C. The Sm(Mg_0.5Ti_0.5)O₃ ceramic incorporated with heavily Bi₂O₃ and B₂O₃ additives exhibits a substantial reduction in temperature (∼250 °C) and compatible dielectric properties in comparison with that of an un-doped one. This implied that this ceramic is suitable for miniaturization in the application of dielectric resonators and filters by being appropriately incorporated with a sintering aid.     

Comparison of covalent and noncovalent interactions of carbon nanotubes on the crystallization behavior and thermal properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

In this study, multiwalled carbon nanotubes (MWCNTs) were dispersed into a poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, in which PHBV was either covalently attached to the nanotubes through an esterification reaction between the carboxylic groups of functionalized MWCNTs and the hydroxyl groups of PHBV with toluene diisocyanate as a coupling agent or physically mixed to result in only noncovalent interactions. The structure, crystallization behavior, and thermal properties of the resulting nanocomposites were studied. We found that the crystallization of PHBV grafted onto the MWCNTs (PHBV‐g‐MWCNTs) was markedly hindered and exhibited an exothermic peak caused by cold crystallization, whereas the nonisothermal crystallization of PHBV was enhanced because a heterogeneous nucleation effect appeared in the PHBV/MWCNTs. Moreover, the maximum decomposition temperature of the PHBV‐g‐MWCNTs was improved by about 14.4°C compared with that of the PHBV/MWCNTs and by about 23.7°C compared with that of the original PHBV. Furthermore, the PHBV‐g‐MWCNTs exhibited the wider melt‐processing window than the PHBV/MWCNTs and original PHBV. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4299–4307, 2013     

The influence of tetrahedral ordering on the microwave dielectric properties of Sr0.05Ba0.95Al2Si2O8 and (M = Al, Ga, M′ = Si, Ge) ceramics

The feldspars Sr_0.05Ba_0.95Al₂Si₂O₈, BaAl₂Ge₂O₈ and BaGa₂Si₂O₈ with S.G. I2/c, and BaGa₂Ge₂O₈ with S.G. P2₁/a, were studied by means of crystal structural and microstructural analyses and dielectric measurements. All the investigated densely sintered single-phase feldspars exhibited a permittivity () of 7–8 and a temperature coefficient of resonant frequency (τ_f) from −20 to −30 ppm/°C. In contrast to the and τ_f the dielectric losses were found to be dependent on the annealing conditions. In Sr_0.05Ba_0.95Al₂Si₂O₈ the Qxf values increased from 42,500 to 92,600 GHz when the annealing time at 1400 °C was increased from 1 to 162 h. Such a difference in the Qxf values as a result of various annealing conditions was attributed to different degrees of tetrahedral ordering. In contrast to aluminosilicate feldspars, Ge-containing feldspars can be sintered and ordered at low temperature. In BaAl₂Ge₂O₈ the Qxf values decreased when the sintering temperature exceeded the order-disorder I2/c ↔ C2/m phase-transition temperature. The BaGa₂Si₂O₈ and BaGa₂Ge₂O₈ feldspars exhibited a rapid decrease of Qxf values when the annealing temperature approached the melting point. However, the BaAl₂Ge₂O₈ and BaGa₂Ge₂O₈ can regain their high Qxf values by annealing at 1000 °C. The BaGa₂Ge₂O₈ stood out from the other investigated feldspars, with a sintering temperature of 1100 °C, Qxf values of 100,000–150,000 GHz and a τ_f of −26 ppm/°C.