冷杀菌技术在食品中的应用

<正> 食品中的细菌、酵母、霉菌等微生物的存在会导致食品在贮藏过程中腐败变质,因此在食品贮藏加工工艺中,如何有效地杀菌或抑菌,是食品加工过程中的重要技术。 自从罐藏技术和巴氏杀菌技术发明以来,热力杀菌已成为食品工业中极为重要的杀菌技术。近几十年米,先后开发了高温短时(HTST)、超高温(UHT)、欧姆加热等新式热力杀菌技术,广泛地应用于流体食品如果汁、奶制品的杀菌,明显提高了产品的质量。但是热力杀菌技术也存在着一些难以克     

板式热交换器与管式热交换器的比较分析

在乳制品生产过程中,对物料的杀菌是不可缺少的工序,常用的杀菌设备是板式热交换器和管式热交换器.为此本文对两种典型的杀菌设备进行比较分析,并从设备的结构、应用的场合等几方面阐述了二者的特点.     

超临界CO2在肉及肉制品杀菌中的应用研究进展

超临界CO2是一种绿色、环保和实用的超临界流体,目前已广泛用于提取各种生物活性物质.近年来,随着非热杀菌技术的兴起,超临界CO2在杀菌方面的研究也显著增加.与冷等离子体、高压脉冲电场和高压CO2等非热杀菌技术相比,超临界CO2的操作温度和压力相对较低,能最大限度保留食品中的营养成分和提高食品的微生物安全性.本文综述超临...     

高新技术在食品加工中的应用

为了进一步提高食品资源利用率和增值加工程度,实现食品工业的可持续发展.介绍超临界流体萃取、膜分离技术等高新技术的原理、特点及其在食品加工、杀菌、检测、保鲜领域的应用.     

食品超高压杀菌研究进展

超高压杀菌作为一种新兴的食品非热处理技术,因具有保持食品固有营养品质、质构、风味、色泽、新鲜程度等优势而成为研究热点.本文系统介绍了超高压食品处理技术的发展概况、特点、杀菌机理、技术优势及其本身存在的问题,并针对杀菌因素如超高压容器、压力大小、加压时间、施压方式、温度、食品添加物、水分活度等方面的研究进展进行了对比分析,提出了食品超高压杀菌的研究方向和研究内容.     

食品加工新型杀菌技术研究进展

食品杀菌是食品加工过程不可或缺的环节之一。本文介绍了食品工业中新型杀菌技术和设备的研究进展,重点阐述了超高压杀菌、微波杀菌、高压脉冲电场杀菌、辐照杀菌、脉冲强光杀菌等新型杀菌技术与装备的研究发展进程,并扼要地介绍了相关技术特点。新型杀菌技术特别是冷杀菌技术可以更好地保持食品品质和风味,保证食品质量安全。     

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。     

现代物理杀菌技术

杀菌是食品生产加工中一个非常重要的环节。通过杀菌,可以有效地防止食品不受病虫害及各种菌类的危害。杀菌根据温度不同可分为热杀菌和冷杀菌,其中冷杀菌又可分为物理杀菌和化学杀菌。传统食品加工主要采用热杀菌,因而食品中热敏成分和营养物质易被破坏,褐变反应加剧,挥发性成分损失等。对于热杀菌不足之处,近年来,随着科技进步,国内外研制开发了一系列冷杀菌技术。据报道,目前先进杀菌技术包括超高压杀菌、静电杀菌、电子射线杀菌、磁场杀菌、强光脉冲杀菌、生物杀菌、容器杀菌等。由此可见,冷杀菌中物理杀菌是目前杀菌技术发展…     

冷杀菌技术及其在食品中应用

冷杀菌技术是一种新技术,既能杀灭食品中微生物、又能最大限度保持食品色泽、香味及营养成分。该文着重介绍超高压杀菌、高压脉冲电场杀菌、脉冲强光杀菌、臭氧杀菌、膜分离杀菌、紫外线杀菌等冷杀菌技术杀菌原理及其在食品中应用。     

食品物理冷杀菌技术研究进展

物理冷杀菌技术是一种新技术,既能杀灭食品中微生物、又能最大限度保持食品色泽、香味及营养成分。该文着重介绍超高压杀菌、高压脉冲电场杀菌、脉冲非热等离子体杀菌、脉冲强光杀菌、磁力杀菌、膜分离除菌、紫外线杀菌、辐照杀菌、微波杀菌、超声波杀菌、电阻杀菌、半导体光催化杀菌等技术的杀菌原理及其在食品中应用。     

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.     

脉冲电场在固体食品加工中的应用

脉冲电场(pulsed electric field, PEF)技术被视为21世纪食品非热加工技术发展史上的里程碑之一。迄今为止, PEF已广泛应用于果汁、牛奶和液态蛋等液体食品的杀菌和钝酶,并朝着商业化道路前进。然而,与PEF在液体食品中的应用相比,其在固体食品中的应用还处于起步阶段。固体食品的表面虽然也富含微生物,但PEF处理这类食品对微生物的影响较小,因此不能将其应用于固体食品的杀菌保鲜。仅管如此, PEF诱导的细胞电穿孔使其可作为一种预处理方法 ,通过增加质量和能量传递效率的方式来进行辅助固体食品的干燥、冻融、烹饪等。因此,本文重点介绍基于PEF细胞响应的高品质食品加工应用,总结PEF处理室的特点及PEF预处理固体食品的相关机制。最后,本文探讨了PEF在固体食品加工中的主要障碍和前景,为PEF未来在食品行业的发展拓宽研究方向。