Quality of shell eggs pasteurized with heat or heat-ozone combination during extended storage

The physical quality and functionality of shell eggs, pasteurized with heat or a combination of heat and ozone, were assessed during eight weeks of storage at 4 or 25 °C. Shell eggs were treated as follows: (1) immersion heating that mimics commercial pasteurization processes (egg internal temperature of 56 ± 0.1 °C for 32 min), or (2) a newly developed combination process comprised of heating (56 ± 0.1 °C, internal, for 10 min) followed by gaseous ozone treatment. Eggs were tested for yolk index, Haugh units, albumen pH, albumen turbidity, and percent overrun. Additionally, albumen samples were assayed for lysozyme activity and free sulfhydryl group content, and were analyzed using differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. Both processed and unprocessed eggs maintained superior quality when stored at 4 °C, as opposed to 25 °C. Pasteurization, regardless of method, led to superior maintenance of Haugh units during storage but also increased albumen opacity and decreased albumen overrun. Detrimental effects on quality markers were more severe in heat-pasteurized eggs than those treated with the ozone-based process. Pasteurization of shell eggs by either process did not affect lysozyme activity or sulfhydryl group content. Changes in protein secondary structure, as indicated by FTIR analysis, suggest that the ozone-based process is less damaging to albumen proteins than is the heat-alone process. In conclusion, heat-ozone pasteurization, by virtue of its less severe heat treatment, yields a safe final product that more closely resembles untreated shell eggs.     

Growth of Salmonella serovars in hens’ egg albumen as affected by storage prior to inoculation

Different Salmonella enterica serovars, including Enteritidis, were tested for growth at 20°C in separated albumen upon inoculation with 39 cfu ml⁻¹. The albumen was fresh or stored for up to 3 weeks prior to inoculation (p.i.) either in the shell egg or separated from the yolk. The serovar Enteritidis did not behave differently than the other serovars indicating that the association between human S. Enteritidis infections and eggs is not due to its growth behaviour in albumen. A pronounced growth occurred more frequently and up to a one-log unit higher level in fresh albumen than in albumen stored p.i. This was at least partly explained by a pH effect. Since growth in the separated albumen was similar when the albumen had been stored p.i. in the absence or presence of yolk, we have no indication that nutrients or factors negating the inhibitory properties of the albumen leak out from the yolk during storage. Growth of Salmonella inoculated at a level of 8 cfu in the albumen of fresh and stored whole shell eggs was studied to simulate a more natural situation. In this case, growth also occurred more frequently when inoculated in the albumen of fresh eggs compared to eggs stored p.i. It can be concluded from our study that cooling practices are recommended shortly after lay to prevent Salmonella from growing in eggs.     

An inverse lumped capacitance method for determination of heat transfer coefficients for industrial air blast chillers

An inverse model using lump body was developed to calculate heat transfer coefficients as a dynamic function of time. The model used sequential function specification algorithm to calculate surface heat flux from transient temperature measurements inside a lump body system. Transient temperature measurements were collected during cooling inside an industrial chiller at two different positions with different air velocities using four replicates for each position. The calculated surface heat flux was found to be very accurate as the maximum value of the root mean squares error (RMSE) for temperature is 0.045 °C, lower than the expected error form thermocouple measurements. The calculated heat flux was then used to calculate heat transfer coefficients as a dynamic function of cooling time followed by calculation of time average heat transfer coefficient using numerical integration. The approach developed here could be a pragmatic powerful dynamic method to model spatial variation of heat transfer coefficients for industrial chillers and freezers.     

Modelling crystal polymorphisms in chocolate processing

Efforts have been devoted over the last decades towards modelling phase change kinetics of fats in chocolate. The fats in chocolate have a number of polymorphic forms and manufacturers must deliver a product with the right polymorph to the consumer. In this work a model was developed that contains only two polymorphs rather than the six polymorphs that can be identified using Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD). This simplification allowed the phase change kinetics to be estimated from a set of DSC experiments. The phase change reactions were coupled with heat transfer and used to successfully predict the temperature profiles and the concentration of polymorphs (within 10%). These quantities determine among others contraction and cohesion, which are essential to demoulding and cleaning processes. Indeed, deposits left on the mould surface leads to undesirable product surface and an increase of cleaning costs. During the rapid cooling step (similar to the FrozenCone process), only a thin layer (to maintain the prescribed shape) of the shell is partially crystallised (typically 20% of the thickness) with unstable crystals (typically 10%) due to the high cooling rates. The model was then used to develop of a rapid cooling process allowing the estimation of the processing time required for the rapid cooling step depending on the thickness of the shell and the temperature of the plunger.     

Laying season and egg shell cracks on the growth of Salmonella enteritidis in the egg albumen during storage

We studied the effects of laying seasons and egg shell cracks on the ability of egg albumen to support the growth of Salmonella Enteritidis (SE) in eggs. Hens eggs used were those laid in February, June, and October in a farm in Japan and stored at 10, 20, and 30 degrees C, and at 30 degrees C after storage at 10 degrees C, immediately after receipt or after cracking the shell. At several-day intervals during storage, the egg contents were poured into a dish, SE was inoculated into albumen, and then the growth of SE during 3 days incubation at 18 degrees C was measured. The results demonstrated that storage temperature and laying season affected the growth of SE in the egg albumen. The proportion of eggs upon which albumen allowed the growth of SE was higher in the eggs stored at 30 degrees C than those stored at 10 degrees C. The growth of SE in eggs was lowest in the following order of laying: February, October, and June. SE grew preferably in albumen of cracked eggs than intact eggs.     

基于COMSOL的平房仓冷却通风过程中粮堆热湿耦合传递研究

粮仓冷却干燥通风是确保储粮安全的重要技术措施,在此过程中粮堆内部的热湿耦合迁移过程非常复杂。在COMSOL软件中,建立了冷却干燥通风过程中高大平房仓的三维物理模型,通过修改COMSOL内置材料方程、耦合渗流、能量守恒、动量守恒和水分迁移控制方程,以实测的送风空气温度和湿度为入口边界条件,数值模拟了湍流、湿空气传热、湿空气传质、多孔介质传热、多孔介质传质等多个物理场,并考虑了热湿耦合、温度耦合和流动耦合,对高大平房仓粮堆内冷却干燥通风过程中的热湿迁移规律进行了研究。基于实际高大平房仓的验证结果表明,通过修改COMSOL内置方程可以准确模拟预测冷却干燥通风过程中粮堆内热湿耦合传递过程,数值模拟结果可用于指导粮仓冷却干燥通风过程和粮仓通风系统优化。     

The effect of short term storage on the albumen quality of shell eggs

Certain physical changes occur naturally in the albumen of shell eggs when stored under cool conditions which cause the thick white to become thin. The whipping characteristics of the albumen are changed during this process but the functional performance of the albumen as measured by the angel food cake method is not affected to any marked degree. Three 10-day storage trials were undertaken using day-old shell eggs which demonstrated that a significant loss of albumen performance did not occur until the storage temperature reached 18 ºC. This conclusion clearly indicates the importance of maintaining shell eggs under cool conditions between collection at the farm and commercial distribution by the egg floors, particularly during the summer season.     

Effect of infectious bronchitis on the structure and composition of egg albumen

In an experimental flock of fowls infectious bronchitis produced reductions in the weights of the whole egg, albumen and shell and a decrease in the ratio of thick + inner thin albumen to outer thin albumen giving the whole albumen a watery appearance. In the thick fraction there was an increase in the water content and a decrease in the concentration of proteins including ovomucin and lysozyme which are believed to combine by electrostatic attraction to form the structural matrix. A reduction in ovomucin concentration was also detected in the outer thin fraction. The deficiency of this protein in the whole albumen was particularly marked and was probably mainly responsible for its abnormal appearance. A reduction in the percentage of ovalbumin I in the albumen proteins occurred in both the thick and the outer thin fractions and in the latter was accompanied by an increase in ovalbumin II. The only other significant changes found in this fraction were increases in the concentrations of sodium and potassium. The estimation of diffusible hexoses and hexosamines provided no evidence that hydrolysis of glycoproteins had occurred. From these and histological findings it was concluded that infectious bronchitis impairs the synthesis of albumen proteins by the magnum.     

鲜鸡蛋中溶菌酶的活性分布

为了研究鸡蛋不同部位溶菌酶的活性,在不破坏蛋体内部结构的情况下,利用注射器和照蛋器抽取蛋内样品(系带与蛋黄膜除外),对鲜鸡蛋各个部分的溶菌酶活性进行分析研究。结果表明：壳外膜及蛋黄中不含溶菌酶,蛋黄膜所含溶菌酶活力最高为9764.290U/mL,其次系带为4172.86U/mL,系带中溶菌酶活力约为其他部位溶菌酶活力的11倍以上;蛋膜黏附蛋白、外稀蛋白、中浓蛋白和内稀蛋白这4个部位所含溶菌酶活力分别为378.714、 330.238、354.929、245.381U/mL,壳外膜和蛋黄不含有溶菌酶。蛋清在蛋内的位置不同,其中溶菌酶活力也存在差异,尖中部及钝端的溶菌酶活性高,而尖端及蛋的中部溶菌酶活性低。     

Thermal death time measurement using thin flexible sleeves: a new experimental approach for determining microbial destruction kinetics in fluids of arbitrary viscosity

The thermal death time kinetics of Salmonella Enteritidis (SE) was measured in buffer, egg yolk, and albumen using thin layer plastic sleeves. The sleeves allowed for the loading and sampling of liquids of high or unusual viscosity, as in the case of yolk and albumen, and accepted relatively large volumes (2 to 3 ml) of fluid. The sleeves maintained the volume of the fluid in a thin layer and could be easily handled for heat exposure. The thin layer maintained one-dimensional heat transfer and minimized temperature gradients, thus preventing parts of the fluid from experiencing different heating rates. A representative strain of SE associated with an egg-based salmonellosis outbreak was used in this study. The D- and z-values of the chosen strain, H7037, were measured in buffer, yolk, and albumen. In buffer, SE had the following mean (±standard deviation) D-values: D(55°C) = 3.51 ± 0.30 min, D(57°C) = 1.75 ± 0.13 min, and D(60°C) = 0.25 ± 0.06 min. In yolk, D(58°C) = 0.90 ± 0.05, D(60°C) = 0.26 ± 0.03, and D(62°C) = 0.20 ± 0.02. In albumen, D(55°C) = 1.26 ± 0.31, D(56°C) = 0.68 ± 0.10, and D(57°C) = 0.44 ± 0.04. The z-values for SE calculated from these D-values were 4.29 ± 0.39°C in buffer, 6.12 ± 0.26°C in yolk, and 4.63 ± 1.14°C in albumen. The sleeves allowed one consistent approach to determining thermal death time kinetics regardless of viscosity.     

贮藏温度-时间变化对壳蛋新鲜度影响研究

该文以新鲜罗曼粉壳蛋为研究对象,研究5个贮藏温度-时间变化组壳蛋新鲜度指标变化,分别于0、10、20、30 d检测所有实验组壳蛋失重率、气室高度、哈夫单位、蛋黄指数、浓稀蛋白比、蛋清pH。结果表明,贮藏期间壳蛋失重率、气室高度和蛋清pH显著升高（P<0.05）,哈夫单位、蛋黄指数和浓稀蛋白比显著下降（P<0.05）。贮藏20 d时,处理组5壳蛋哈夫单位和蛋黄指数显著高于（P<0.05）对照组1、处理组1、处理组2和处理组3,而失重率、气室高度、蛋清pH较低（P<0.05）。贮藏30 d时,处理组5壳蛋失重率和气室高度显著低于对照组1、处理组1和处理组3（P<0.05）,蛋黄指数显著高于对照组1、处理组2、处理组3、处理组4（P<0.05）。除失重率、哈夫单位外,对照组2与处理组5壳蛋新鲜度指标整体差别不大。因此,除了壳蛋自身品质外,需要尽可能延长低温（4 ℃）贮藏时间,延缓壳蛋新鲜度指标劣变。     

鸡蛋蛋黄的功能及其制品

鸡蛋富含营养价值高的蛋白质，脂质，也是维生素和矿物质的良好来源，特别是其中的蛋白质人体吸收率达99．7％，且必需氨基酸十分丰富。鸡蛋不仅是个营养宝库，而且作为快餐食品，糕点和面包的食品原料，蛋白与蛋黄的热凝笥，蛋白的起泡性，蛋黄的乳化性等特性在食品工业上也得到普遍的应用。     

矩形肋槽烘缸内壁面的传热系数

将传热学的理论和实验成果应用于矩形肋槽烘缸内壁面的传热工作中,分析了饱和水蒸气在烘缸内壁的肋顶面及肋侧面的冷凝传热和冷凝水在肋槽底部的对流传热并推导出这3种情况下传热系数的具体计算公式,以期为烘缸向纸张的传热计算提供依据。初步研究表明,宽和短的肋有利于增强肋槽烘缸的传热,内壁面的热阻最小、壁壳的热阻次之、外壁面的热阻最大。     

贮藏温度变化对壳蛋新鲜度的影响

该文以新鲜罗曼粉壳蛋为研究对象,研究4个贮藏温度变化处理组壳蛋新鲜度指标的变化,分别于0、10、20、30 d检测所有实验组壳蛋失重率、气室高度、哈夫单位、蛋黄指数、浓稀蛋白比和蛋清pH。结果表明,贮藏10～30 d,处理组2、处理组3、处理组4的失重率显著升高(P<0.05),而气室高度和浓稀蛋白比显著降低(P<0.05),除对照组外,所有处理组壳蛋pH呈现先升高后下降的趋势,处理组3和处理组4的蛋黄指数下降趋势更为明显。对照组和处理组1壳蛋的哈夫单位、蛋黄指数和浓稀蛋白比显著高于(P<0.05)处理组3和处理组4。在贮藏10～20 d时,处理组2的壳蛋pH显著高于(P<0.05)对照组和处理组1。因此,如果前10 d常温贮藏温度≥20℃时,引起壳蛋失重率的增加和哈夫单位的下降,与低温(4℃)贮藏相比,采用贮藏温度变化(常温-低温)贮藏壳蛋更容易引起壳蛋新鲜度指标的下降。     

Rheological,surface and colorbvietric properties of egg albumen gel affected by pH

Abstract

Studies were conducted to evaluate the effects of albumen at naturally existing pH ranges on the functional and gel characteristics. Albumen was obtained from freshly laid shell eggs. The pH of albumen was altered using either IN NaOH or IN HC1 to obtain a pH of 7.5, 8.0, 8.5, 9.0, 9.5 and 10.0. The altered albumen was tested for its foaming capacity (FC), foam stability (FS), and bake volume (BV). Albumen gels were prepared and tested for firmness (FM), strain at failure (NF), and stress at failure (SF) as well as their color attributes (Hunter L, a, and b). In general, FC and BV of the albumen decreased (P<0.05) as the pH increased. The BV of the albumen was affected by FS than FC for all the adjusted pH ranges. A denser structure was observed for albumen gels as the pH increased. The FM, NF and SF of albumen gels increased, and Hunter L and a values decreased with the increasing adjusted pH. The FM, NF, SF and Hunter L value of albumen gel could be used as quality indicators in evaluating the changes of texture and color with pH.     

OVERALL HEAT TRANSFER COEFFICIENTS AND AXIAL TEMPERATURE DISTRIBUTION IN A TRIPLE TUBE HEAT EXCHANGER

Computation of overall heat transfer coefficients in a triple tube heat exchanger (TTHE) is more complicated than in the case of a double tube heat exchanger (DTHE) as the two overall heat transfer coefficients are not independent of one other. A new procedure was developed to calculate these overall heat transfer coefficients and an effective overall heat transfer coefficient value for known inlet and outlet temperatures, and heat capacities of the fluids (product and heating/cooling medium). In this study, this newly developed procedure was utilized and the overall heat transfer coefficients and axial temperature distribution of fluids were computed for a cooling process for different flow rates and inlet temperatures of the fluid streams. The effectiveness of the TTHE was compared to that of a DTHE of identical length. It was observed that when the fluids were flowing in a cocurrent manner, the temperature of the cooling medium with lower heat capacity exceeded the temperature of the product before the fluids exit the TTHE, which caused a decrease in the effectiveness of the TTHE.     

Chitosan coating minimises eggshell breakage and improves egg quality

The interior quality of eggs, shell impact strength, and consumer perception of eggs coated with chitosan containing an organic acid (acetic, lactic and propionic) were evaluated. Uncoated eggs had the highest albumen pH and lowest albumen viscosity. The viscosity of eggs coated with chitosan and lactic or propionic acids were the highest. Chitosan coating also improved shell strength with chitosan + lactic acid being the best coating in this regard. The colour of shell and yolk as measured by lightness (L*), a*, b*, chroma and hue of coated and uncoated eggs were not significantly different but the difference was detected in the colour of albumen, which is an effective indication of freshness and egg quality. Based on sensory evaluation, consumers could not differentiate coated eggs from uncoated eggs; thus the general acceptability of the coated eggs was the same as uncoated eggs. This study shows a great potential of using chitosan and lactic acid mixture as a coating material for egg coating to extend the shelf life. It has no effect on consumer acceptability of the product. Copyright © 2007 Society of Chemical Industry     

基于微型风扇阵列系统的人体降温空调服

论证基于微型风扇阵列的人体降温空调服的概念,并从理论和实验方面对其可行性进行评估。通过数值求解各类典型热环境条件下的三维Pennes生物传热方程,揭示出在皮肤表面引入微型风扇阵列时,其强化散热作用可显著降低体表的温度水平。同时,还采用红外成像技术及热电偶测温方式,对模拟人体的发热块经受风扇阵列强化散热作用前后的降温情况进行实验测定,进一步证实微型风扇阵列的高效降温特性,期望引申出新一代可灵活调节的空调服。     

基于CFD技术的折流杆换热器的性能分析

折流杆换热器是为了避免管束振动而开发的一种新型管束支撑换热器,近年来在国内外得到了广泛应用。但限于换热器结构的复杂性,其壳程流体的流动和换热细节信息还不甚清楚。为了进一步掌握折流杆对壳程流体的强化传热机理,基于CFD技术研究了折流杆换热器壳程流体流动和传热性能,为折流杆换热器的结构优化提供了理论依据。     

Physicochemical and functional properties of shell eggs following electron beam irradiation

Low dosages of electron beam irradiation (EBI) were applied to shell eggs to examine potential effects on physicochemical and functional properties. Prior to the assessment of physicochemical and functional properties, the antimicrobial efficacy of 2, 3 and 4 kGy dosages of EBI in shell eggs was established by the reduction of inoculated Listeria monocytogenes, Escherichia coli and Salmonella typhimurium to an undetectable level. Physicochemical changes to shell eggs receiving the same dosages of EBI were quantified by Haugh unit, free sulphhydryl groups, yolk index and lipid oxidation. Functional properties were assessed by foaming capacity, emulsifying capacity and gelling properties. A loss of thick albumen and a corresponding increase in free sulphhydryl groups in the albumen were observed after EBI, resulting in a loss of foam volume and gel hardness. Negligible changes in yolk index and lipid oxidation paralleled a retention of emulsifying capacity and gelling properties. EBI proved to be an effective method for controlling microbial growth in shell eggs without adversely affecting physicochemical and functional properties. © 2002 Society of Chemical Industry