Microwave assisted freezing part 2: Impact of microwave energy and duty cycle on ice crystal size distribution

Among innovative freezing processes, electromagnetic wave assistance during freezing has received great attention in recent years. The literature provides interesting studies indicating that smaller ice crystals may be obtained during freezing with the assistance of microwaves. In the companion paper, we designed a laboratory scale prototype to perform experiments of this type in well controlled conditions at 2.45 GHz. In the current study, we performed freezing experiments using this prototype and developed a protocol to measure ice crystal sizes using X-ray micro-tomography. The methodology was first validated by measuring ice crystal distribution in unidirectional conventional freezing. Then several microwave assisted freezing modalities were studied. Experiments were conducted with pulsed and continuously applied microwaves. The impact of microwave irradiation time was studied at a constant incident microwave power, and then at constant energy supplied to the system. We observed a significant reduction of up to 25% in ice crystal size when microwave assistance was used during freezing with both pulsed and continuously applied microwaves. These observations tend to disconfirm the hypothesis in the literature according to which ice crystal size reduction is due to temperature oscillations. The only remaining hypothesis in the literature is that ice crystal size reduction may be due to the perturbation of the H-bond network in water, which could be a precursor to crystalline structure. It appeared that at constant incident microwave power, the increase in irradiation time tended to decrease ice crystal size. No significant difference in ice crystal size reduction was observed for a constant energy supplied to the system. The amount of energy supplied by microwaves seems to be a factor influencing ice crystal size.Industrial relevanceMicrowave assisted freezing is an emerging process which permits reducing ice crystal size, and thus improving frozen product quality. The measurement of ice crystals in samples frozen in controlled conditions of both freezing and microwave irradiation allows studying the main parameters that induce the reduction of their size. Better understanding of the relevant factors influencing nucleation and/or crystal growth can help to optimize the process.     

Combined convective and microwave assisted drying: Experiments and modeling

The drying process is largely used in many different industrial applications, such as treatment of foods, production of cosmetics and pharmaceuticals, manufacturing of paper, wood and building materials, polymers and so on.     

Impact of magnetic assisted freezing in the physicochemical and functional properties of egg components. Part 1: Egg white

Effects of freezing assisted with magnetic fields (MFs) in a Cell Alive System (CAS) commercial unit at 50 °C, with a static MF only (0% CAS) and with a static MF plus oscillating MF (10% CAS) on egg white (W) was investigated. W samples were from commercial eggs from three strains of laying hens (two of them living in fortified cages and the third one in liberty at outdoor). The main goal was to follow the protein thermal denaturation involved in W processing. Thermal denaturation enthalpy was markedly affected (~ 50% total protein in comparison with fresh sample) but similar for both MFs processes, where 0% CAS was taken as Control freezing treatment. MFs effects were predominantly thermal in nature and constituted the factor with the highest influence on thermal behavior, as well as on the majority of the functional properties exhibited by MFs samples. Rheology and free Sulfhydryl content were studied complementarily to Differential Scanning Calorimetry (DSC) data. Some important functional properties as Foaming parameters and Texture of W gel were also determined. The hen strains-feeding factor did not practically influence the physical or functional behaviors of both untreated and processed W samples.     

Microwave inactivation of Escherichia coli K12 CIP 54.117 in a gel medium: Experimental and numerical study

This study evaluates the efficiency of the inactivation of Escherichia coli K12, entrapped within calcium alginate gel, by microwave processing compared to a conventional approach i.e. by heating in a water bath. Microbial thermal inactivation equations coupled with heat transfer and Maxwell’s equations are integrated into a 3D Finite Elements model under dynamic heating conditions. Water bath microbial inactivation experimental data are exploited for performing parameter identification of a non-linear microbial model, and the Calcium alginate gel’s dielectric properties were numerically estimated. The coupled model provides a very good fitting to the experimental results. The simulation have shown uneven temperature distribution during microwave heating which may interpret its lower inactivation efficiency comparing to the conventional water bath treatment. This study also demonstrates the reliability of the coupled modeling approach to estimate the efficiency of the microbial inactivation, despite the thermal heterogeneity inherent in the microwave treatment.     

Experimental investigation and numerical simulation of three-point bending fatigue of 3D orthogonal woven composite

This paper reports the three-point bending fatigue behavior of three-dimensional (3D) orthogonal woven composite (3DOWC) in experimental and finite element analysis (FEA) approach. In experimental, the S–N curve was obtained to illustrate the relationship between applied stress levels and number of cycles to failure. The stiffness variation was recorded to present the degradation of mechanical properties of the 3DOWC during the process of fatigue loading. Furthermore, the fatigue damage morphologies of the tested 3DOWC coupons were given to indicate the damage modes of different parts (resin, yarns, and their interface) of the composite under the range of stress levels. In FEA approach, a user-defined material subroutine UMAT which characterizes the stiffness matrix and fatigue damage evolution of the 3DOWC was developed and incorporated with a finite element code ABAQUS/Standard to calculate the maximum deflection of the 3DOWC during each loading cycle. The bending deformation at different loading cycles was also calculated. From the comparisons between FEA and experimental approaches, it is indicated that the proposed model is reasonable for calculating the fatigue bending deformation.     

虾仁热物性的计算及冻结时间的数值模拟

在虾仁热物性参数计算和等效比热容处理潜热的基础上,采用有限差元法对不规则虾仁建模,分别预测虾仁对称截面距冰箱冷冻层底部15,50,100mm处的冻结时间,在该基础上,对冰箱冻结虾仁进行实验验证。通过数值模拟与实验验证结果的对比发现,模拟冻结时间与实验冻结时间曲线相关系数为0.996,虾仁切面中心测点的最大误差值为1.85K,说明该数值模拟方法可以有效预测食品冻结过程中温度分布,对虾仁的冷冻加工、品质控制以及设备的优化具有重要意义。     

Ultrasound assisted nucleation of some liquid and solid model foods during freezing

Power ultrasound has been proven to be useful in promoting the nucleation of ice in water-based solutions, and different mechanisms have been proposed to describe this phenomenon. In the present work, the use of ultrasound waves to induce dynamic nucleation in deionised water, sucrose solution, and agar gel samples was studied, and the mechanism of ultrasound assisted nucleation was discussed. The samples were frozen in an ethylene glycol–water mixture (− 20 °C) in an ultrasonic bath system after putting them into tubing vials. Ultrasound irradiation (25 kHz, 0.25 W cm⁻¹) was applied continuously for 1, 3, 5, 10 or 15 s at different sample's temperatures in the range of 0 °C to − 5 °C. The nucleation temperatures of the water, sucrose solution and agar gel samples without ultrasound irradiation, occurred stochastically at − 7.4 ± 2.4 °C, −10.6 ± 1.7 °C and − 7.5 ± 0.92 °C, respectively and followed normal distributions. Unlike agar gel samples, the nucleation temperatures of water and sucrose were induced by applying ultrasound for 5 s at different temperatures after a short delay, and linear relationships between the ultrasound irradiation temperatures and the nucleation temperatures were observed. Evaluation of the effect of different durations of ultrasound application on agar gels indicated that 1 s was not long enough to induce nucleation, 3 s was optimal, 5 s and 10 s produced heat and inhibited nucleation, and 15 s did not exhibit significant differences from 3 s and 10 s. It was concluded that longer irradiation durations (especially 5 s and 10 s) caused the sample to heat up, which interrupted or delayed the nucleation. Ultrasound irradiation for 3 s induced nucleation in agar gel samples at different temperatures resulting in a linear relationship between irradiation and nucleation temperatures. The observations indicated that the Hickling's theory, according to which vigorous collapses of bubbles are the only driving mechanism of nucleation, is not adequate to describe the ultrasound assisted nucleation. The results, however, were in agreement with results of some other researchers suggesting that secondary phenomena such as flow streams are also important for the initiation of nucleation. In conclusion, the use of ultrasound as a means to control the crystallisation process offers promising application in food freezing, though further investigations are needed for understanding the mechanisms, especially in solid foods.     

Environmental impact of pyrolysis of mixed WEEE plastics part 1: Experimental pyrolysis data

Growth in waste electrical and electronic equipment (WEEE) is posing increasing problems of waste management, partly resulting from its plastic content. WEEE plastics include a range of polymers, some of which can be sorted and extracted for recycling. However a nonrecyclable fraction remains containing a mixture of polymers contaminated with other materials, and pyrolysis is a potential means of recovering the energy content of this. In preparation for a life cycle assessment of this option, described in part 2 of this paper set, data were collected from trials using experimental pyrolysis equipment representative of a continuous commercial process operated at 800 °C. The feedstock contained acrylonitrile-butadiene-styrene and high impact polystyrene with high levels of additives, and dense polymers including polyvinylchloride, polycarbonate, polyphenylene oxide, and polymethyl methacrylate. On average 39% was converted to gases, 36% to oils, and 25% remained as residue. About 35% of the gas was methane and 42% carbon monoxide, plus other hydrocarbons, oxygen and carbon dioxide. The oils were almost all aromatic, forming a similar mixture to fuel oil. The residue was mainly carbon with inorganic compounds from the plastic additives and most of the chlorine from the feedstock. The results showed that the process produced around 70% of the original plastic weight as potential fuel.     

速冻食品的冰晶形态及辅助冻结方法研究进展

文章简述了食品速冻技术以及不同冻结速度下形成的冰晶形态及观测冰晶的方法,综述了压力辅助冻结、电场辅助冻结以及磁场辅助冻结等技术在近几年的研究进展。直接法能直接观察到冻结过程形成的冰晶,而间接法则是通过观察冻结后冰晶在食品内部留下的间隙来分析冰晶特征。压力辅助冻结能提高过冷度,在压力释放时水分瞬间冻结,使形成的冰晶细小且分布均匀;电场辅助冻结能降低成核温度促使形成更小尺寸的冰晶;磁场辅助冻结能增强氢键抑制冰晶的生长,3种辅助冻结方式有利于提高冷冻食品的品质,具有良好的应用前景。     

微波辅助羧甲基玉米淀粉的制备及其上浆性能

为获得对纯棉高支纱线具有优良上浆效果的浆料,以玉米淀粉为原料,一氯乙酸为醚化剂,氢氧化钠为催化剂,微波辅助制备了一种亲水改性淀粉浆料羧甲基玉米淀粉(CMCS)。借助红外光谱仪和扫描电子显微镜对产物的分子结构和颗粒形态进行分析,并对其理化特性及对纯棉纤维的黏附性进行研究。结果表明：玉米淀粉大分子上成功引入了羧甲基取代基团, CMCS 颗粒出现不同程度破损,完整性遭到破坏;CMCS 的特性黏数和表观黏度降低,流动性增强,其溶解性、膨胀性和糊透明度提高,抗凝沉性增强,蓝值下降,直链淀粉发生降解;CMCS 的糊化温度下降,糊化性能和糊加工性能得到改善;CMCS 黏附性能相比于原淀粉最高可增加27. 9%,并且随着取代度的提高,黏附性逐渐增强。对9. 67 tex 纯棉纱上浆实验结果表明,CMCS 浆纱的力学性能显著提高,其浆纱的断裂增强率与耐磨增强率分别比原淀粉浆纱增加了118. 5%和88. 7%,伸长率降低了29. 7%。     

A steady-state biofilm model for simultaneous reduction of nitrate and perchlorate, part 1: model development and numerical solution

A multispecies biofilm model is developed for simultaneous reduction of nitrate and perchlorate in the H(2)-based membrane biofilm reactor. The one-dimension model includes dual-substrate Monod kinetics for a steady-state biofilm with five solid and five dissolved components. The solid components are autotrophic denitrifying bacteria, autotrophic perchlorate-reducing bacteria, heterotrophic bacteria, inert biomass, and extracellular polymeric substances (EPS). The dissolved components are nitrate, perchlorate, hydrogen (H(2)), substrate-utilization-associated products, and biomass-associated products (BAP). The model explicitly considers four mechanisms involved in how three important operating conditions (H(2) pressure, nitrate loading, and perchlorate loading) affect nitrate and perchlorate removals: (1) competition for H(2), (2) promotion of PRB growth due to having two electron acceptors (nitrate and perchlorate), (3) competition between nitrate and perchlorate reduction for the same resources in the PRB: electrons and possibly reductase enzymes, and (4) competition for space in the biofilm. Two other special features are having H(2) delivered from the membrane substratum and solving directly for steady state using a novel three-step approach: finite-difference for approximating partial differential and/or integral equations, Newton-Raphson for solving nonlinear equations, and an iterative scheme to obtain the steady-state biofilm thickness. An example result illustrates the model's features.     

山药糖蛋白微波辅助提取及抗氧化活性研究

采用正交实验得出了微波辅助提取山药糖蛋白的优化实验条件,即微波功率200W、提取时间1min、料液比1:10.山药提取液经脱蛋白、透析,乙醇沉淀物经DEAE-52及Sephadex G-75柱层析得到一种糖蛋白组分,经SDS-聚丙烯酰胺凝胶电泳,相对分子量为35200Da.利用α-脱氧核糖法、邻苯三酚自氧化法进行抗氧化实验,结果表明,该糖蛋白有一定抗氧化能力.     

Microwave and ultrasound assisted extraction of phytocompounds from black jamun pulp: Kinetic and thermodynamics characteristics

The present study focuses on the extraction of phenolic compounds, anthocyanin and antioxidants from black jamun pulp by microwave and ultrasound assisted extraction process. The microwave-assisted extraction was carried out for 240 s at microwave power level of 100–400 W. The yield of total anthocyanin and total phenolic content in the microwave assisted extraction process at 400 W power level after an extraction period of 240 s was 8.197 mg of C3G g⁻¹ and 37.671 40.632 mg GAE g⁻¹, respectively. The ultrasound assisted extraction was performed at temperatures of 40, 50, 60, and 70 °C for 150 min. In the ultrasound assisted extraction at a sonication temperature of 70 °C, the yield of anthocyanin was 8.525 mg of C3G g⁻¹, while the yield of the phenolic compound was 47.331 mg GAE g⁻¹. The pseudo-second order model was found to be the most suitable model to represent the extraction kinetics of anthocyanin, phenolic compounds, and antioxidant activity of black jamun pulp. The effective diffusion coefficient for ultrasound assisted extraction of phenolic components, anthocyanin, and antioxidant activity in the temperature range of 40-70 °C was 5.704× 10⁻¹²–10.515 10⁻¹², 2.485× 10⁻¹² -8.507× 10⁻¹², and 2.061× 10⁻¹²–11.977 × 10⁻¹² m².s⁻¹ respectively. The negative Gibbs free energy change values for extraction of phenolic compounds and anthocyanin specified that the reaction was feasible and spontaneous. Thermodynamic parameters such as positive enthalpy change and positive entropy change indicated that the ultrasound assisted extraction process was endothermic and irreversible in nature.     

数值模拟在食品冻融过程中的应用进展

文中介绍了有限差分法、有限元法和有限体积法3种应用广泛的离散方式,并对新兴的无网格法在模拟食品冷冻过程时做了简要分析;分析了导热方程与传质方程或电磁方程的耦合这一关键问题,并比较了几种潜热处理方法的优缺点;讨论了人工神经网络法在模拟食品冻融过程时的优势与不足;对近年来热门的微波解冻与射频解冻的数值模拟做了详细论述。     

微波协同离子液体的合成及在黄酮类化合物提取中的研究进展

阐述了离子液体的合成方法,并进行了系统的比较,微波协同合成离子液体具有耗时短、产率高及环境友好等优点;同时总结了微波协同合成离子液体的国内研究进展,并综述了离子液体在黄酮类化合物提取中的应用.     

微波法和水蒸气蒸馏法提取丁香精油的研究

以丁香为原料,分别采用微波法和水蒸气蒸馏法提取精油,探讨微波萃取对丁香精油提取率和精油品质的影响。以丁香精油提取率为指标,通过正交试验优化微波提取条件,采用气相色谱-质谱(GC-MS)法鉴定其化学成分,并与水蒸气蒸馏法提取的精油进行比较。结果表明,微波萃取丁香精油的最佳工艺参数为微波功率300 W、料液比1∶4(m∶V)、微波时间25s、提取次数4,该条件下精油的提取率可达到20.65%,远远高于水蒸气蒸馏法的11.33%;从该精油中鉴定出19种成分,其中3种丁香精油有效成分的得率分别为丁香酚13.2%、石竹烯4.4%、乙酰基丁香酚2.2%,石竹烯和乙酰基丁香酚得率分别是水蒸气蒸馏精油的2.8倍和2倍。微波萃取是丁香精油较有效的提取方式。