含颗粒液态食品通电加热加工特性及影响因子

通电加热技术不同于传统杀菌加工技术 ,它在加工连续流体食品特别是含颗粒食品方面 ,显示出了巨大的优越性及发展潜力。文中介绍了含颗粒液态食品通电加热加工特性及影响通电加热食品品质的若干因素。     

美拉德产物-果胶负载CoQ10纳米颗粒的制备及研究

采用大豆分离蛋白-燕麦β-葡聚糖美拉德产物(SPI-OG)和果胶(PEC)通过复凝聚反应制备出三元复合物作为壁材,以CoQ₁₀为芯材利用超声-乙醇注入法制备CoQ₁₀纳米颗粒。探究制备壁材及CoQ₁₀纳米颗粒的工艺条件,并对样品进行结构表征及稳定性和功能性质研究。结果表明,pH 3.8、总质量浓度5 mg/mL、SPI-OG与PEC的质量比1∶1时制备的壁材是最为稳定的;芯壁质量比1∶7.5是制备纳米颗粒的最佳比例,包埋率和负载量分别为70.58%和8.61%。结构表征方面,红外光谱、X-射线衍射、差示扫描量热的结果均可证实CoQ₁₀被包埋在壁材中。储存稳定性研究表明低温以及避光可以很好地储存CoQ₁₀纳米颗粒。功能性质方面,CoQ₁₀包埋后其DPPH清除自由基的能力没有太大变化,胃肠道模拟发现CoQ₁₀纳米颗粒的溶出度明显高于CoQ₁₀的溶出度,说明CoQ₁₀纳米颗粒的制备基本上没有破坏C...     

二氧化氯气体处理对果蔬采后生理代谢及质量安全的影响

二氧化氯（ClO₂）气体是国际上公认的安全、无毒绿色消毒剂,其具有杀菌性强、扩散性和穿透性好、不发生氯的替代反应、无毒副作用等优点,已在农业、食品、医药等领域应用广泛。近年来,ClO₂在果蔬保鲜领域得到很好的应用,成为研究热点。本文论述了ClO₂气体对采后果蔬中乙烯和呼吸、膜脂、苯丙烷类、能量等生理代谢及果蔬失水软化、外观和营养等贮藏品质方面的影响,并讨论了ClO₂气体对果蔬致病、致腐微生物的杀菌机理及其杀菌效果,同时分析了ClO₂气体在果蔬保鲜中的应用限制,最后,根据目前的应用研究现状对存在的问题进行总结,并对其未来的应用前景进行了展望,旨在为拓宽ClO₂气体在果蔬保鲜领域的广泛应用提供参考。     

臭氧微纳米气泡在食品杀菌中的应用

阐述微纳米气泡的理化特性和臭氧的强氧化性,研究臭氧微纳米气泡应用于食品杀菌的可行性,主要从微纳米气泡的理化特性、制备方法、表征方法,以及臭氧微纳米气泡在水处理、果蔬清洗和水产品杀菌中的应用进行阐述,并对臭氧微纳米气泡在食品杀菌中的应用进行展望,以期促进臭氧微纳米气泡在食品领域的研究和应用。     

叶绿素镁钠盐对液态食品中Staphylococcus aureus的光动力杀菌研究

以叶绿素镁钠盐为光敏剂,研究了其对几种液体食品中金黄色葡萄球菌的光动力杀菌效果。结果表明,叶绿素镁钠盐对几种液态食品中的金黄色葡萄球菌具有很强的杀菌效果,其中以10-5mol/L的叶绿素镁钠盐杀菌效果最佳,10 min金黄色葡萄球菌减少了4.5个对数;随着光照时间的延长,液态食品中的金黄色葡萄球菌的致死率明显增加,特别是在起始10 min内;一般透光性好的食品包装材料对液态食品中金黄色葡萄球菌光动力杀菌效率没有影响,但液态食品的pH对其杀菌效率有一定的影响。对于不同的液态食品,在澄清或酸性的食品中叶绿色镁钠盐的光动力杀菌效果较好,但当食品中含固体颗粒或较浑浊时,其杀菌效率显著降低。     

二氧化硅包覆银铜纳米颗粒的结构及其抗菌性能

为研究双金属纳米颗粒间协同抗菌作用及防止金属纳米颗粒团聚,利用气溶胶一步法制备了“火龙果”型高负载量(50%)二氧化硅包覆银铜双金属纳米颗粒抗菌剂Ag-Cu/SiO₂。借助X射线衍射仪、透射电子显微镜、电子能谱仪对Ag-Cu/SiO₂的结构进行研究,并测试该材料对金黄色葡萄球菌和大肠杆菌的最低抑菌浓度(MIC)及细菌的时间与杀菌曲线,研究了2种细菌胞内活性氧的生成情况。结果表明:银铜双金属纳米颗粒均匀分散在球型二氧化硅内部,呈现“火龙果”型结构;与Cu/SiO₂和Ag/SiO₂相比,相同负载量(50%)的Ag-Cu/SiO₂有更好的抗菌效果,对2种细菌的MIC值均为2 μg/mL,在24 h内可以充分抑制细菌生长;Ag-Cu/SiO₂生成活性氧的水平明显高于单金属纳米颗粒,致使细菌死亡,从而说明双金属纳米颗粒具有协同抗菌作用。     

柔性ZrO2纳米纤维膜的制备及其应用研究现状

针对现有制备方法获得二氧化锆(ZrO₂)纳米纤维膜柔性不足的问题,综述了近年来利用静电纺丝技术在制备柔性ZrO₂纳米纤维膜方面的研究进展。基于现有研究成果,从前驱体溶液、静电纺丝工艺和煅烧温度3方面系统阐述了静电纺制备柔性ZrO₂纳米纤维膜的工艺流程,并概述了纤维形貌、孔隙结构和晶体结构对柔性ZrO₂纳米纤维膜的影响,介绍了柔性ZrO₂纳米纤维膜在能源、生物等领域的应用。最后指出:采用静电纺丝技术制备的柔性ZrO₂纳米纤维膜具有比表面积大、耐热性高等一系列优异特性,但仍存在纤维膜韧性相对较差的缺陷,尚无法满足实际工况要求;提高柔性ZrO₂纳米纤维膜的整体力学性能,并进行批量化制造,以满足实际应用是未来研究的重点。     

酿造酱油热力杀菌规程研究

目的 研究酿造酱油杀菌条件并对其进行验证，最终得出酿造酱油的杀菌规程。方法 测定金黄色葡萄球菌增菌稀释后，在80℃、85℃、90℃加热条件下，对残留活菌进行计数，计算出D值、Z值和F值，再通过直接对酿造酱油产品进行热穿透实验，最终得出合理的杀菌规程。结果 杀菌规程为：D_80℃=6.13 min,r²=0.909 4;D_85℃=4.78 min,r²=0.901 0;D_90℃=1.53 min,r²=0.680 2;Z值为16.6℃；F_80℃=36.78 min;F_85℃=28.68 min;F_90℃=9.18 min。通过理论计算得出最佳杀菌温度和时间为90℃，9.18 min；经过实际加工过程验证，确定出最终的杀菌规程为：36min-4 min/90℃。结论 细菌致死是一个累积的过程，是产生理论与实际差异的最主要因素，因此在实际应用过程中，除了理论计算，验证工作更为重要。     

基于液态光子晶体固定化的柔性结构生色膜制备及其性能

针对光子晶体材料结构稳定性较差的问题,以光固化型单体取代常规组装介质水制备液态光子晶体,通过紫外光聚合固化构建纳米微球嵌入弹性体式的非密堆积阵列光子晶体,制备结构稳定的柔性光子晶体结构生色膜,并对其结构和性能进行分析。结果表明:液态光子晶体的光学性质可通过胶体体系中SiO₂纳米微球的体积分数及其粒径进行调控,随SiO₂体积分数由22%增大至40%,其微球间的平均间距逐渐减小,液态光子晶体结构色蓝移;固定SiO₂微球体积分数,当其粒径由123 nm增加至178 nm时,液态光子晶体结构色红移;液态光子晶体色彩鲜艳、饱和度高,经紫外光辐照后,所构建的固态光子晶体膜具有明显的虹彩效应和优异的柔韧性,并表现出显著的力致变色性能,展示了其在智能可穿戴纺织材料领域良好的应用潜能。     

杀灭芽孢杆菌的方法及机理的研究综述

芽孢杆菌在不利条件下产生内生芽孢,芽孢壁厚且对外界环境有较强抵抗力,常规杀菌方法不易将其杀灭。芽孢在食品中萌发形成营养细胞,严重降低食品安全性,威胁消费者健康。文章从芽孢杆菌在食品中产生的危害出发,对热杀菌、高压杀菌、气体杀菌、化学杀菌以及促萌发杀菌等方法进行分析,比较其杀灭芽孢杆菌的效果以及优缺点。并对其杀菌机理进行探讨,指出膜受体、离子通道、核蛋白以及酶类对芽孢杆菌的影响。以期为芽孢杆菌的研究和控制提供理论参考和技术支撑。     

Heat Transfer Enhancement in Thermal Processing of Tomato Juice by Application of Nanofluids

In this research, our chief aim was to survey possible improvements in thermophysical properties of nanofluids when they are used as heating mediums for time reduction and energy saving in food industries for the first time. Accordingly, three different variables of temperature (70, 80, and 90 °C), alumina nanoparticle concentration (0, 2, and 4 %), and time (30, 60, and 90 s) were selected for thermal processing of tomato juice by a shell and tube heat exchanger. Our results revealed that incorporation of nanoparticles could raise density, viscosity, and thermal conductivity and decrease heat capacity, but this increasing/decreasing trend was linear or non-linear depending on the diameter of the nanoparticles. Four percent Al₂O₃–water, compared with 2 % nanofluid and pure water (0 % nanofluid), had the highest overall heat transfer coefficients for all Re numbers. Incorporating nanoparticles into the base heating fluid of water could augment the effectiveness of the heat exchanger by 49 %. Thermal processing time of tomato juice was shorter for 2 and 4 % nanofluids, compared with water, by 22.23 and 46.29 %, respectively; this time reduction caused energy saving rates for 2 and 4 % nanofluids to be improved by 22.3 and 48.76 %, respectively.     

Fluid to Particle Heat Transfer Coefficients in Holding Tube Having Noncircular Cross Section

ABSTRACT: Convective heat transfer coefficient (h_p) between fluid and particle in continuous tube flow were compared for 2 configurations of holding tubes: one conventional having a circular cross section (CHT) and the other having noncircular cross section (NCHT). A stream of plastic spheres was fed into the holding tube to simulate a food system with particulates. Live vegetative cells of Bacillus stearothermophilus were immobilized in aqueous gellan cubes and injected into the holding tubes with water as a carrier medium. The observed inactivation levels were compared with predicted values calculated from transient heat transfer equations solved by an explicit finite difference technique. Mean effective h_p values ranged from 400 to 2500 W/m².K for the NCHT and 350 to 1700 W/m².K for the CHT at a Reynolds numberrpanging from 6000 to 13000. The difference in h_p levels between the 2 configurations increased with the flow rate and temperature. Although no relation was observed between h_p values and liquid to particle relative velocity, a trend between pipe Reynolds number and h_p values was observed. The presence of a large number of particles in the holding tube significantly influenced h_p values. Keywords: heat transfer coefficients, holding tube, Reynolds number, particle     

A model for heat transfer in cryogenic food freezing

An experimental study of the heat transfer between liquid nitrogen sprays and a model food (a gelatine slab) was carried out under conditions similar to those in a cryogenic freezer. Measurements of heat flux and local mass flow rates of the spray were made at various liquid N₂ pressures and various temperature differences between the spray and the food surface.
At higher spray pressures, the heat transfer coefficient increases with the mass flux density of the liquid available at the food surface. The quantity of liquid nitrogen sprayed onto the solid surface, the mean droplet size, spray velocity, surface coverage and the mean temperature difference between the boiling nitrogen and the food surface are major factors influencing the rate of heat transfer during the freezing process. Although the heat transfer coefficients at the food surface are much less than those obtained for individual droplets, the model provides useful data.
The results are critically discussed in relation to cryogenic freezing of foods.     

Nano-fluid thermal processing of watermelon juice in a shell and tube heat exchanger and evaluating its qualitative properties

Due to specific thermophysical properties of nanofluids, compared with conventional thermal fluids (steam and hot water), their application in diverse industries, to improve heat transfer and to save energy, has increased. One important aspect of applying nanofluid thermal processing is shortening the process time which could have high potentials in the food industry since nutritional and bioactive components would be maintained much higher than common thermal processes. In this project, possibility of replacing water with alumina-water nanofluids (2 and 4% concentrations) during high temperature short time processing (75, 80 and 85 °C for 15, 30 and 45 s) of watermelon juice in a shell and tube exchanger regarding its qualitative properties (lycopene, vitamin C, color, pH and TSS) was investigated. Reduction in process time when applying 2 and 4% nanofluids, up to 24.88 and 51.63%, had considerable effects on maintaining qualitative properties for watermelon juices. For instance, thermal processing by 0, 2 and 4% nanofluids at 75 °C for 15 s could keep 81.15, 84.81 and 91.28% of lycopene and 61.11, 63.70 and 67.04% of vitamin C, respectively. pH and TSS indices of processed watermelon juices were in the range of 5.58–5.82 and 9.0–9.4, respectively, showing no considerable correlation with the heating media used in thermal processing. Our results revealed that nutritional and physicochemical properties of watermelon juice processed with alumina nanofluids were better than common thermal processing by water with 9.89, 6.18 and 50.38% higher lycopene, vitamin C and color retention in the final product, respectively.Industrial RelevanceEven so thermal processes are effective in preventing microbial spoilage of fruit juices, high volume of energy transfer in long durations into food products with heat sensible ingredients or properties results in biochemical and nutritional losses, development of unpleasant reactions, changes in overall quality of food products, and high energy consumption. Nowadays, consumers demand for food products with long shelf lives, high quality and proper prices are increasing. So, to meet these demands, food industries are looking for alternative thermal technologies to reduce losses in food characteristics and process costs, and introduce a fresh, nutritious, healthy and affordable food produce.Thermal conductivity of conventional fluids is much lower than metals and oxidized metals. For example, thermal conductivities of copper and alumina are 700 and 60 times higher than the thermal conductivity of water, respectively. Accordingly, fluids with suspended particles of metals or oxidized metals benefit from better heat transfer properties. The term of Nanofluid refers to each stable two-phase compound that includes both base fluids and nanoparticles (lower than 100 nm, at least in one dimension).There is no research dealing with effects of adding nanoparticles to conventional thermal fluids for fruit juices processing. So, the goal of this research was to introduce nanofluid technology for thermal processing of food products for the first time, increasing heat transfer efficiency in shell and tube exchangers by nanofluids and frugality in energy consumption for pasteurization, reducing thermal processing duration and better quality retention of food products.     

Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work’s objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for “quick estimation” purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process.     

Temperature Mapping of Particles During Aseptic Processing with Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) was used to obtain 2-dimensional temperature maps in potatoes undergoing aseptic processing. The change in precession frequency of protons served as the temperature indicator. The larger particles (6.9 and 3.84 cm3) showed a δT (T_surface - T_center) of up to 22±0.4°C 45s after exiting the heat exchanger with the δ (T_outlet - T_inlet) of the carrier fluid in the heat exchanger at 30 to 45°C. No AT was measured between the center and the surface of particles <2.05 cm³ pumped at <22.7 L/min. The average fluid to particle convective heat transfer coefficient (h_fp) for the heat exchanger and holding tube was calculated using a finite element method. The hfp was from 600 to 2500 and >3000 W/m²°C for the large (6.9 cm³ cubes) and smaller particles respectively.     

Sorbic acid diffusivity in relation to the composition of high and intermediate moisture model gels and foods

The diffusivity at infinite diffusant dilution ( D ₀) of sorbic acid in high and intermediate moisture gels (with various substrates and water contents) and in three foods was evaluated. The determination of D ₀(25°C) was achieved by tridimensional diffusion in gels cubes or by monodimensional diffusion in infinite food columns. For the same substrate concentration by weight, D₀ values of sorbic acid in concentrated sugar solutions decreased slightly when the molecular weight of the sugar was increased. When a liquid substrate such as glycerol was used, D ₀ values referred to equal concentrations by weight, were higher than in sugar solutions. The diffusion of sorbic acid is related, as a first approximation, to the water content rather than to the water activity of the diffusion medium.     

FLUID-TO-PARTICLE CONVECTIVE HEAT TRANSFER COEFFICIENT AS EVALUATED IN an ASEPTIC PROCESSING HOLDING TUBE SIMULATOR

A pilot scale aseptic processing holding tube simulator was fabricated for evaluating fluid-to-particle convective heat transfer coefficients at temperatures up to 110C. the simulator was calibrated to give carrier fluid flow rate as a function of CMC concentration, temperature, pump rpm and pipe diameter. Fluid-to-particle heat transfer coefficients (h_fp) were estimated with model and real food particles held stationary in a moving liquid. Data were gathered under various conditions: CMC concentration (0- 1.0% w/w), flow rate (1.0 - 1.9 × 10⁻⁴m³/s) and particle size (diameter: 21 and 25.4 mm; length: 24 and 25.4 mm). Depending on operating conditions, average heat transfer coefficients (h_fp) ranged from 100 to 700 W/m²C with corresponding Biot numbers (Bi) ranging from 10 to 50. CMC concentration, fluid temperature and flow rate, as well as their interactions, had significant effect (p < 0.05) on h_fp for both Teflon and potato particles. Some differences were observed with respect to the associated h_fp for Teflon and potatoes due probably to differences in their structural/textural characteristics. Heat transfer coefficient associated with cooling were significant ly lower (p < 0.05) than those associated with heating.     

Use of Artificial Neural Network to Predict Temperature, Moisture, and Fat in Slab-Shaped Foods with Edible Coatings During Deep-Fat Frying

ABSTRACT: An artificial neural network (ANN) was developed to predict heat and mass transfer during deep-fat frying of infinite slab-shaped foods coated with edible films. Frying time, slab half-thickness, film thickness, food initial temperature, oil temperature, moisture diffusivity of food and film, fat diffusivity through food and film, thermal diffusivity of food, heat transfer coefficient, initial moisture content of food, and initial fat content of food (mf_o) were inputs. Temperature at the center (T₁), average temperature (T_ave), fat content (mf_ave), and moisture content (m_ave) of food were outputs. Four ANNs with 50 nodes each in 2 hidden layers with learning rate = 0.7 and momentum = 0.7 provided most accurate outputs, that is maximum absolute errors for T₁ and T_ave were < 1.2 °C, < 0.004 db for m_ave, and < 0.003 db for mf_ave. The predictions of mf varied linearly with mf.     

Modeling inactivation of Clostridium botulinum and vitamin destruction of non-Newtonian liquid-solid food mixtures by convective sterilization in cans

Unsteady fluid mechanics and convective heat transfer in the sterilization of canned tuna chunks immersed in a non-Newtonian fluid by a Darcy-Brinkmann-Forchheimer porous model has been studied numerically by a conjugate mathematical model. The coupled equations were solved by the Finite Volume method with the SIMPLE algorithm. The model developed related the sterilization time and temperature distribution with the kinetics of C. botulinum inactivation and the degradation of two relevant vitamins in canned tuna, riboflavin, and thiamin. Additionally, the effect of the covering liquid in the sterilization process and nutrients loss from canned tuna was investigated. The results showed that the sterilization time decreases in fluids with low viscosity, as water and brine, compared to CMC. The cases investigated had a different response to achieve complete sterility, considering the preservation of nutrients. Obtaining a balance between operating time and energy cost allows improving the process to make it more efficient.Industrial relevanceModeling of bacteria inactivation and vitamin degradation in liquid-solid food mixtures is of great interest because the extended number of relevant food processes involve heat transfer in these matrices, where is mandatory an accurate estimation of time and conditions essential for a complete sterilization process.