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In this paper, we propose a new mixed finite element method, called stabilized mixed finite element method, for the approximation of steady reaction–diffusion partial differential equations (PDEs). The method is obtained by translating the primal second-order PDEs into a first-order mixed system, and then adding some suitable elementwise residual terms multiplied by a stabilization parameter to the weak formulation. The new method is compatible, i.e., the added terms equal to zero in the continuous case. Furthermore, it is mesh-independent, i.e., the stabilization parameter is independent of the mesh size. We prove both coercive and continuous properties in a weighted norm for the corresponding new mixed bilinear formulation. These assure that the finite element function spaces do not require to satisfy the classical Ladyzhenkaya–Babuska–Brezzi (LBB) consistency condition. Therefore, the widely used Lagrange finite element can be adopted. A simple proof of a priori error estimate with lower order regularity requirement is discussed, and numerical experiments confirm the efficiency and reliability of the new stabilized mixed method. Finally, the method is applied to solving unsteady reaction–diffusion equations. Error estimates are also given, and numerical examples still support the theoretical analysis very well. [ABSTRACT FROM AUTHOR]

This article studies superconvergence phenomena of the split least-squares mixed finite element method for second-order hyperbolic equations. By selecting the least-squares functional properly, the procedure can be split into two independent symmetric positive definite subprocedures, one of which is for the primitive unknown and the other is for the flux. Based on interpolation operators and an auxiliary projection, superconvergent H1 error estimates for the primary variable u and L2 error estimates for the introduced flux variable σ are obtained under the standard quasiuniform assumptions on finite element partition. A numerical example is given to show the performance of the introduced scheme. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 222-238, 2014 [ABSTRACT FROM AUTHOR]

In this article, a characteristic finite element approximation of quadratic optimal control problems governed by linear convection-diffusion equations is given. We derive some a posteriori error estimates for both the control and the state approximations, where the control variable is constrained by pointwise inequality. The derived error estimators are then used as an error indicator to guide the mesh refinement. In this sense, they are very important in developing adaptive finite element algorithm for the optimal control problems. Finally, a numerical example is given to validate the efficiency and reliability of the theoretical results. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2013 [ABSTRACT FROM AUTHOR]

In this paper, we examine the method of lumped masses for the approximation of convex optimal control problems governed by linear parabolic equations, where the lumped mass method is used for the discretization of the state equation. We derive some a priori and a posteriori error estimates for both the state and control approximations with control constraints of obstacle type. Numerical experiments are given to show the efficiency and reliability of the lumped mass method. [ABSTRACT FROM AUTHOR]

In this paper, we consider the variable-order time fractional mobile/immobile diffusion (TF-MID) equation in two-dimensional spatial domain, where the fractional order α (t) satisfies 0 < α ⁎ ≤ α (t) ≤ α ⁎ < 1. We combine the quadratic spline collocation (QSC) method and the L 1 + formula to propose a QSC- L 1 + scheme. It can be proved that, the QSC- L 1 + scheme is unconditionally stable and convergent with O (τ min ⁡ { 3 − α ⁎ − α (0) , 2 } + Δ x 2 + Δ y 2) , where τ , Δ x and Δ y are the temporal and spatial step sizes, respectively. With some restrictions on α (t) , the QSC- L 1 + scheme has second order convergence in time even on the uniform mesh, without any restrictions on the solution of the equation. We further construct a novel alternating direction implicit (ADI) framework to develop an ADI-QSC- L 1 + scheme, which has the same unconditionally stability and convergence orders. In addition, a fast implementation for the ADI-QSC- L 1 + scheme based on the exponential-sum-approximation (ESA) technique is proposed. Moreover, we also introduce the optimal QSC method to improve the spatial convergence to fourth-order. Numerical experiments are attached to support the theoretical analysis, and to demonstrate the effectiveness of the proposed schemes. [ABSTRACT FROM AUTHOR]

In this paper, a Crank-Nicolson block-centered finite difference method is first developed and analyzed for the nonlinear regularized long wave equation. By using a cutoff technique, second-order convergences both in time and space are proved under a suitable time-space stepsize constraint condition. To further improve the computational efficiency, an efficient two-grid block-centered finite difference method is introduced and analyzed, in which a resulting small-scale nonlinear problem is first solved on a coarse grid space of size H , and then a resulting large-scale linear problem is solved on a fine grid space of size h. Under a rough time-space stepsize constraint condition Δ t = o (H 1 / 4) , optimal-order error estimates for both the primal variable and its flux are derived on non-uniform spatial grids. Thus, the proposed method is competitive both in accuracy and efficiency compared with the fully nonlinear Crank-Nicolson block-centered finite difference scheme. Numerical experiments are presented to verify the theoretical analysis. • An efficient TG-CN-BCFD method is proposed for the RLW equation. • Optimal-order error estimates on non-uniform spatial grids are rigorously proved. • The estimate is derived under a very rough constraint condition Δ t = o (H 1 / 4). • Numerical experiments are given to show accuracy and efficiency of the method. [ABSTRACT FROM AUTHOR]

Checking whether a pushdown automaton is simulated – in the sense of a simulation pre-order – by a finite-state automaton is EXPTIME-complete. This paper shows that the same computational complexity is obtained in a probabilistic setting. That is, the problem of deciding whether a probabilistic pushdown automaton (pPDA) is simulated by a finite Markov decision process (MDP) is EXPTIME-complete. The considered pPDA contain both probabilistic and non-deterministic branching. The EXPTIME-membership is shown by combining a partition-refinement algorithm with a tableaux system that is inspired by Stirling's technique for bisimilarity checking of ordinary pushdown automata. The hardness is obtained by exploiting the EXPTIME-hardness for the non-probabilistic case. Moreover, our decision problem is in PTIME when both the number of states of the pPDA and the number of states in the MDP are fixed. [ABSTRACT FROM AUTHOR]

As one of the most vital energy conversation systems, the safe operation of wind turbines is very important; however, weak fault and time-varying speed may challenge the conventional monitoring strategies. Thus, an entropy-aided meshing-order modulation method is proposed for detecting the optimal frequency band, which contains the weak fault-related information. Specifically, the variable rotational frequency trend is first identified and extracted based on the time–frequency representation of the raw signal by constructing a novel scaling-basis local reassigning chirplet transform (SLRCT). A new entropy-aided meshing-order modulation (EMOM) indicator is then constructed to locate the most sensitive modulation frequency area according to the extracted fine speed trend with the help of order tracking technique. Finally, the raw vibration signal is bandpass filtered via the corresponding optimal frequency band with the highest EMOM indicator. The order components resulting from the weak fault can be highlighted to accomplish weak fault detection. The effectiveness of the proposed EMOM analysis-based method has been tested using the experimental data of three different gear fault types of different fault levels from a planetary test rig. [ABSTRACT FROM AUTHOR]

We develop a fast divide-and-conquer indirect collocation method for the homogeneous Dirichlet boundary value problem of variable-order space-fractional diffusion equations. Due to the impact of the space-dependent variable order, the resulting stiffness matrix of the numerical scheme does not have a Toeplitz structure. In this paper, we derive a fast approximation of the coefficient matrix by the means of a finite sum of Toeplitz matrices multiplied by diagonal matrices. We show that the approximation is asymptotically consistent with the original problem, which requires O (N log 2 N) memory and O (N log 3 N) computational complexity with N being the numbers of unknowns. Numerical experiments are presented to demonstrate the effectiveness and the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This research performed the process optimization of wheat flour crisp puffing by radio frequency (RF) and investigated the accompanying property changes of starch. Experiments were performed in a 6 kW, 27.12 MHz pilot‐scale RF system. The results showed that the volume expansion was highest (220%) when the conditions were employed as follows: electrode gap (115 mm); height of the sample (55 mm); initial moisture content of the sample (30%). Under these conditions, the samples were puffed at 120 s by RF, and changes in the starch properties were further observed. The results showed that the structure of the starch was destroyed, changing from oval and spherical in shape to fragmented. The crystal type of the starch changed from A to A + V types. Its crystal order was reduced, and the Fourier‐infrared spectrum showed that the ratio of (1048/1022) cm−1 decreased from 1.142 to 1.047. The crystallinity decreased from 48.27% to 17.57%. These changes will help starch digestion and absorption in human body. These results indicated that RF puffing could become a potential development method for puffed snacks. Practical Application: In this study, the processes of radio frequency puffing wheat flour chips were optimized, and the changes of starch properties during puffing were studied. Therefore, this research provided a theoretical basis for the industrial application of radio frequency puffing. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) heating has been studied to inactivate bacteria in some powder foods. In this study, a 6 kW, 27.12 MHz RF system was used to pasteurize Salmonella in black fungus (Auricularia auricula) powder. The effects of different conditions (initial aw, electrodes gaps, particle sizes) on RF heating rate and uniformity were investigated. The results showed that RF heating rate was significantly (p < 0.05) improved with decreasing electrodes gap and increasing initial aw, and the heating rate was the slowest when the particle size was 120–160 mesh. However, these factors had no significant (p > 0.05) influence on heating uniformity. RF pasteurization of Salmonella in black fungus powder was also studied. The results showed that, to inactivate Salmonella for 5 log reductions in the cold spot (the center of surface layer), the time needed and bacteria heat resistance at designated temperature (65, 75, 85 °C) decreased with increasing aw, and the first order kinetics and Weibull model could be used to fit inactivation curves of Salmonella with well goodness. Quality analysis results showed that although RF pasteurization had no significant (p > 0.05) effect on Auricularia auricula polysaccharide (AAP) and total polyphenols, obvious changes were found on color. Results suggested that RF pasteurization can be considered as an effective pasteurization method for black fungus powder. [ABSTRACT FROM AUTHOR]

Relative permeability controls the flow of multiphase fluids in porous media. The estimation of relative permeability is generally solved by Levenberg-Marquardt method with finite difference Jacobian approximation (LM-FD). However, the method can hardly be used in large-scale reservoirs because of unbearably huge computational cost. To eliminate this problem, the paper introduces the idea of simultaneous perturbation to simplify the generation of the Jacobian matrix needed in the Levenberg-Marquardt procedure and denotes the improved method as LM-SP. It is verified by numerical experiments and then applied to laboratory experiments and a real commercial oilfield. Numerical experiment indicates that LM-SP uses only 16.1% computational cost to obtain similar estimation of relative permeability and prediction of production performance compared with LM-FD. Laboratory experiment also shows the LM-SP has a 60.4% decrease in simulation cost while a 68.5% increase in estimation accuracy compared with the earlier published results. This is mainly because LM-FD needs 2 n ( n is the number of controlling knots) simulations to approximate Jacobian in each iteration, while only 2 simulations are enough in basic LM-SP. The convergence rate and estimation accuracy of LM-SP can be improved by averaging several simultaneous perturbation Jacobian approximations but the computational cost of each iteration may be increased. Considering the estimation accuracy and computational cost, averaging two Jacobian approximations is recommended in this paper. As the number of unknown controlling knots increases from 7 to 15, the saved simulation runs by LM-SP than LM-FD increases from 114 to 1164. This indicates LM-SP is more suitable than LM-FD for multivariate problems. Field application further proves the applicability of LM-SP on large real field as well as small laboratory problems. [ABSTRACT FROM AUTHOR]

The optimum conditions of radio frequency explosion puffing (RFEP) of yam-wheat-cornstarch snacks were explored. The impact of electrode gap (180–190 mm), sample thickness (1–4 mm), and sample height (10–40 mm), on the heating rate and heating uniformity, was evaluated. The process parameters (puffing temperature: 60–100 °C; puffing pressure difference: 0.08–0.28 MPa; residence time: 5–25 min) for the production of snacks were optimized by using quadratic-orthogonal-rotation combination design (QORCD) and response surface methodology (RSM). The quality of snacks was evaluated in terms of crispness, hardness, color difference ΔE, and moisture content. The best quality snacks were obtained with optimized conditions of electrode gap of 185 mm, geometry of 50 × 2 × 20 (length × thickness × height) mm, puffing temperature of 81 °C, puffing pressure difference of 0.17 MPa, and residence time of 16 min. The product qualities reached experimentally under the optimized conditions were 14 of crispness, 3117.36 g of hardness, 7.96 of color difference ΔE, and 12.88% (w. b.) of moisture content. Radio frequency explosion puffing could become a potential method for developing nutritious puffed snacks. [ABSTRACT FROM AUTHOR]

Non-uniform heating of RF energy is the main obstacle for its large-scale application in blanching. In this study, we proposed a new blanching method: steam (ST)-assisted radio frequency (RF) blanching of fresh-cut stem lettuce cuboids. The relative peroxidase (POD) activity, heating uniformity, and physicochemical properties of samples treated by steam-assisted RF blanching at different conditions (RF-50 °C + ST-2.5 min, RF-65 °C + ST-2 min, and RF-80 °C + ST-1 min) were evaluated in comparison with single RF heating and steam blanching. Both the temperature distribution images and the heating uniformity index indicated that steam-assisted RF blanching overcame the defect of local overheating of single blanching mode and achieved more uniform temperature distribution. Besides steam-assisted RF, blanched reduced the thermal damage to cells, which can be demonstrated by lower relative electrolyte leakage rate, thereby maintained better texture, color, and higher vitamin C retention at the same relative POD activity of 5%. Among the three steam-assisted RF blanching treatments, RF-80 °C + ST-1 min achieved optimum heating uniformity and quality of samples. This study suggested that steam-assisted RF blanching can be used as a potential blanching method to improve inactivation efficiency of enzyme and quality of fruits and vegetables. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) heating has been utilized to investigate sterilization techniques, but the mechanism of sterilization via RF heating, particularly on Bacillus cereus (B. cereus), has not been thoroughly examined. In this paper, sterilization processes and potential bactericidal mechanisms of B. cereus using RF were investigated. The best heating and sterilization efficiency was achieved at (Electrode gap 130 mm, conductivity of bacterial suspension 0.1 S/m, volume of bacterial suspension 40 mL). Heating a suspension of B. cereus to 90 °C in 80 s using RF reduced the number of viable bacteria by 4.87 logarithms. At the cellular level, there was a significant leakage of nucleic acids and proteins from the bacterial cells. Additionally, the integrity of the cell membrane was severely damaged, with a decrease in ATP concentration of 2.08 mM, Na, K-ATPase activity to 10.7 (U/109 cells), and Ca, Mg-ATPase activity to 11.6 (U/109 cells). At the molecular level, transcriptomics analysis showed that RF heating of B. cereus to 65 °C produced 650 more differentially expressed genes (DEGs) compared with RF heating to 45 °C. The GO annotation analysis indicated that the majority of differentially expressed genes (DEGs) were predominantly associated with cellular components. KEGG metabolic analysis showed enrichment in microbial metabolism in diverse environments, etc. This study investigated the potential bactericidal mechanism of B. cereus using RF, and provided some theoretical basis for the research of the sterilization of B. cereus. • RF energy significantly inactivated B. cereus. • RF disrupted the cellular structure of B. cereus and reduced its physiological activity. • Transcriptomic analysis was used to reveal changes in gene levels in B. cereus. • Elevated RF heating temperature led to more DEGs in B. cereus. [ABSTRACT FROM AUTHOR]

The sharp H 1 -norm error estimate of a finite difference method for two-dimensional time-fractional diffusion equation is established, where the Caputo time-fractional derivative term is approximated by Alikhanov scheme on graded mesh. Under reasonable assumption that the exact solution has typical weak singularity at initial time, the temporal convergence order of the fully scheme is O (N − min { r α , 2 } ) and the error bound does not blow up when α approximates 1 −. The theoretical analysis utilizes an improved discrete fractional Grönwall inequality, and the correctness of the theoretical result is verified by numerical experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pre-freezing treatment could increase the cell membrane permeability and reduce cell wall's storage modulus of purple sweet potatoes. • Pre-freezing treatment could improve the puffing volume, texture and porosity of radio frequency explosion puffing (RFEP) purple sweet potato chips, and better retaining anthocyanin content. • Higher freezing temperatures and more freezing times would cause the collapse of the tissue structure, restrict the migration of internal water, and hinder volume expansion. • Samples frozen once at −40°C had the best puffing quality and overall acceptability. Radio frequency explosion puffing (RFEP) is a novel oil-free puffing technique used to produce crispy textured and nutritious puffed snacks. This study aimed to investigate the effects of freezing at different temperatures (−20 °C, −40 °C, −80 °C) for14 h and freezing times (1 and 2 times) on the cellular structure of purple sweet potato and the quality of RFEP chips. The analysis of cell microstructure, conductivity, and rheology revealed that higher freezing temperatures and more freezing times resulted in increased damage to the cellular structure, leading to greater cell membrane permeability and decreased cell wall stiffness. However, excessive damage to cellular structure caused tissue structure to collapse. Compared with the control group (4 °C), the RFEP sample pre-frozen once at −40 °C had a 47.13 % increase in puffing ratio and a 61.93 % increase in crispness, while hardness decreased by 23.44 % (p < 0.05). There was no significant change in anthocyanin retention or color difference. X-ray microtomography demonstrated that the RFEP sample pre-frozen once at −40 °C exhibited a more homogeneous morphology and uniform pore distribution, resulting in the highest overall acceptability. In conclusion, freezing pre-treatment before RFEP can significantly enhance the puffing quality, making this an effective method for preparing oil-free puffing products for fruits and vegetables. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) heating is a new technology applied to puffing drying that has the potential to replace conventional drying methods. The heating and puffing effects of sample thickness (1–3 mm), electrode gap (110–130 mm), and moisture content (40–60%), of the composite purple sweet potato chips were studied. The optimal process parameters were 1 mm sample thickness, 110 mm electrode gap, and 60% moisture content. The effects of four drying methods, including RF, microwave (MW), vacuum freezing (VF), and hot air (HA), on the chips were compared. The physicochemical properties of the chips were evaluated in terms of nutrient composition, color, hardness, rehydration ratio, moisture content, and microstructure. The RF-dried samples showed the second-highest anthocyanin retention of 8.74 mg/100 mg, the smallest color difference Δ E of 8.67, a satisfactory hardness of 752 gf, and the highest rehydration ratio of 3.42. Microstructure analysis revealed that RF drying could gelatinize the majority of the starch granules and change their structure. Future studies should focus on minimizing the adverse impact of RF heating to maintain the quality of nutritious snacks. • Purple sweet potato dough could be heated more quickly and evenly at 27.12 MHz. • Heating and puffing effects were affected by radio frequency (RF) process parameters. • RF obtained the lowest color change and satisfactory hardness. • Microstructure analysis revealed that RF can gelatinize the majority of the starch. • RF, as an alternative method, can produce nutritious puffed snacks. [ABSTRACT FROM AUTHOR]

It is known that the well-posedness of time-fractional reaction–diffusion models with Mittag-Leffler kernel usually requires non-physical constraints on the initial data. In this paper, we propose a variable-order time-fractional reaction–diffusion equation with Mittag-Leffler kernel and prove that the aforementioned constraints could be eliminated by imposing the integer limit of the variable fractional order at the initial time, which mathematically demonstrates the physically-relevance of the variable-order modifications. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) heating is a novel technology applied to drying and puffing. In the previous study, the optimal conditions for RF drying and puffing of composite purple sweet potato chips were 60% initial moisture content, 1 mm sample thickness, and 110 mm electrode gap. The effects of RF treatment temperature (50–110 °C) on the quality, physicochemical properties, and starch structure of composite purple sweet potato chips were further studied in this research. With the increase in RF treatment temperature, the protein, starch, and anthocyanin content in the samples were significantly reduced. However, the reducing sugar content, gelatinization degree, water absorption index (WAI), and water soluble index (WSI) were greatly improved. No new functional groups were produced after RF treatment. The starch changed from A-type to B-type crystal structure at temperature of 65 °C, which may result in the formation of a new double helix structure. Moreover, a larger irregular structure was observed at low temperatures of 50–65 °C, while this structure disintegrated into debris at high temperatures of 80–110 °C. This study provided a theoretical foundation for applying RF drying and puffing technology to starchy foods. • Composition of the sample was influenced significantly by RF treatment. • Starch gelatinization was promoted by RF drying and puffing. • Thermodynamic properties were analyzed by DSC. • Structure features were analyzed by XRD and FT-IR. • Starch crystal structure was greatly changed by RF. [ABSTRACT FROM AUTHOR]

The microorganism control in packaged tofu by radio frequency (RF) heating combined with antimicrobial agents was investigated. The inactivation of vegetative cells and spores by RF heating alone or in combination with antimicrobial agents was evaluated. Results showed that vegetative cells of typical food microorganisms, such as E. coli, S. aureus , and Bacillus subtilis , were completely inactivated by RF heating at 80 °C for 20 min, while no significant reduction in the population of spores was observed. Additionally, the growth of Bacillus spores was effectively inhibited by 0.312 mg/g of nisin. The total viable count (TVC) in RF-treated packaged tofu was below 2 log CFU/g during the storage at 4 or 37 °C for 10 days in the presence of nisin. Furthermore, the quality analysis indicated that the pH, texture, color, and volatile profile of samples were well maintained, which contributed to the favorable sensory acceptance of the consumers. These results suggested that effective microorganism control in packaged tofu was achieved by combining RF heating and nisin. The developed method was recommended to prevent spoilage of packaged tofu and extend its shelf-life. [Display omitted] • Typical food microorganisms in packaged tofu were inactivated by RF heating. • 0.312 mg/g of nisin could effectively inhibited the growth of Bacillus spores. • Effective microbial control was realized by combined RF heating and nisin. • Favorable quality properties and sensory acceptance were obtained during storage. [ABSTRACT FROM AUTHOR]

This paper is focused on the effects of radio frequency (RF) heating on the relative activity of polyphenol oxidase (PPO), weight loss, texture, color, and microstructure of potatoes. The results showed that pure mushroom PPO was almost completely inactivated at 80 °C by RF heating. The relative activity of potato PPO reduced to less than 10% with increasing temperature (25–85 °C). Enzyme extract showed the lowest PPO relative activity at 85 °C after RF treatment, followed by the potato cuboids and mashed potato, about 0.19 ± 0.017%, 3.24 ± 0.19%, and 3.54 ± 0.04%, respectively. Circular dichroism analysis indicated that RF heating changed the secondary structure of PPO, as α-helix content decreased. Both electrode gap and temperature had significant effect ( P  < .05) on weight loss, color, and texture of the potato cuboids. Microstructure analysis showed the changes of potato cell and starch during RF heating. [ABSTRACT FROM AUTHOR]

Yogurt is one of the most popular dairy products fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The present study introduced dielectric properties as a new technique for yogurt fermentation monitoring. Dielectric properties of cow milk and yogurt at different time of fermentation were measured from 10 to 3000 MHz at 42 °C using open-ended coaxial-line probe technology by an impedance analyzer. Meanwhile, pH and titratable acidity of yogurt at different fermentation time were measured. Results showed that the dielectric loss factor of yogurt was positively correlated with fermentation time and had an irregular change at the endpoint of fermentation (7 h, pH ≈ 4.6). The polynomial determination coefficients of dielectric loss factor with pH and titratable acidity decreased with increasing frequency and were found highest at 10 MHz (0.927 and 0.963, respectively). The linear coefficients of determination between measured values and calculated values were 0.990 for titratable acidity and 0.965 for pH at 10 MHz, respectively. Accordingly, dielectric loss factor can be a promising indicator for online monitoring of industrial yogurt fermentation process. [ABSTRACT FROM AUTHOR]

• RF heating inactivates HRP at 70 °C and 90 °C. • RF heating changes the secondary and tertiary structures of HRP. • Conformational deterioration is responsible for the enzyme inactivation. • Conformational changes of enzyme vary with temperature and electrode gap. The effects of radio frequency (RF) heating on horseradish peroxidase (HRP) activity and its structure were investigated in this paper. The HRP was heated to 50 °C, 70 °C and 90 °C at different electrode gaps (100, 110 and 120 mm). The relative enzyme activity was 105.33 %–113.73 % at 50 °C, 91.11 %–93.05 % at 70 °C and 47.05 %–68.17 % at 90 °C. Ultraviolet–visible, circular dichroism and fluorescence spectra were used to monitor the variation in secondary and tertiary structure. The results showed that RF heating at the electrode gaps of 120 mm contributed to more severe enzyme inactivation and conformational destruction, which can be explained by the changes in Soret band, secondary structure content and tryptophan fluorescence intensity. This study revealed that enzyme inactivation by RF heating was associated with loss of helical structure, unfolding of enzyme protein and ejection of heme group. [ABSTRACT FROM AUTHOR]

[Display omitted] • A speed-adjustable motor was introduced for improving RF heating uniformity. • LOX of sweet corn was inactivated effectively by RF heating. • Blanching treatments destroyed cell walls and membranes. • Damage to the microstructure deteriorated the physiochemical properties. This study investigated the effects of radiofrequency (RF) and boiling-water (BW) blanching on lipoxygenase (LOX) activity, physicochemical properties, and changes in the cellular morphology of sweet corn kernels. First, a speed-adjustable device was introduced to rotate the sample for improving heating uniformity. Then, the maximum RF heating rate and uniform temperature distribution of samples were obtained under 160 mm electrode gap, 120 g sample weight, and 14 r/min rotating speed. With increased RF heating temperature ranging from 50 °C to 80 °C, the residual activity of LOX significantly decreased to 4.68%. Samples blanched by RF treatment maintained better color, texture, and nutrient content than those by BW when similar levels of enzyme inactivation were achieved. Micrographs also showed the cells were increasingly damaged with increased RF heating temperature, whereas the cells were damaged much more severely when treated with BW. Besides, microscopic destruction of cells also explains the changes in physicochemical properties. [ABSTRACT FROM AUTHOR]

Compared with traditional hot water (HW) blanching, radio frequency (RF) has the advantages of faster heating rate and higher penetration depth. The aim of this study was to explore the optimum conditions of RF blanching of apple slice and compare the quality of apple subjected to RF and HW. Results showed that the optimum heating rate and uniformity can be obtained when electrode gap was of 120 mm, sample geometry of 50 × 8 × 50 mm, and not superimposed of apple slices, which were used for further RF blanching. It required 111 s and 270 s to reach the target temperature (85 °C) in RF and HW blanching respectively. After treated by RF and HW for 120 s, the residual enzyme activities of PPO of apples were 0% and 61.42 ± 1.48% (P < 0.05), the hardness were 402.83 ± 11.93 g and 469.39 ± 10.24 g (P < 0.05), the weight loss were 10.23 ± 1.01% and 14.39 ± 2.58% (P > 0.05), respectively. There was no significant difference (P > 0.05) in color change. • Radio frequency (RF) heating efficiently inactivated the PPO of apple slices in 120s. • The heating time of hot water (HW) blanching is more than twice that of RF. • RF-blanched apples showed greater hardness, weight and color than did apples blanched by HW. • RF blanching holds potential as an industrial blanching method for fruits. [ABSTRACT FROM AUTHOR]

Packed tofu was produced by reheating the mixture of preheated soymilk and coagulant in a sealed container. This study aimed to replace the conventional heating method with RF heating during the reheating of soymilk for packed tofu production. In this study, dielectric properties (DPs), thermal properties (TPs), and rheological properties of soymilk were determined. A mathematical model was developed to simulate the RF heating process of soymilk to determine the appropriate packaging geometry. Water holding capacity (WHC), texture analysis, color measurement, and microstructure observation were performed to evaluate the quality of RF-heated packed tofu. Results showed that soymilk added with Glucono-Delta-Lactone (GDL) coagulated at the temperature above 60 °C, and the loss factor (ε″) was slightly reduced when soymilk was converted to tofu at coagulation temperature. Based on the simulation results, the cylindrical vessel ( φ5 0 mm × 100 mm) was chosen as the soymilk container for desired heating rate (5.9 °C/min) and uniformity ( λ  = 0.0065, 0.0069, 0.0016 for top, middle, and bottom layers). The texture analysis revealed that the hardness and chewiness of packed tofu prepared by RF heating were enhanced (maximum 1.36 times and 1.21 times) compared with commercial packed tofu, while the springiness were not significantly changed. Furthermore, the denser network structure was observed inside RF-heated packed tofu by SEM. These results indicated that packed tofu prepared by RF heating was of higher gel strength and sensory quality. RF heating has the potential to be applied in packed tofu production., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)