制冷与制热空调服的研究进展

针对人体在高温或高寒环境中长时间工作可能导致中暑、热痉挛、低体温症等疾病的问题,在介绍人体体温调节基本原理和换热机制的基础上,着重介绍了利用制冷或制热空调服对人体体温进行主动调节的基本原理,同时归纳和总结了现阶段各类制冷制热空调服的工作原理,并比较了其优缺点。在制冷空调服领域,着重介绍了空气冷却、相变冷却、冰袋冷却、液体冷却等主被动降温方法;在制热空调服领域,着重介绍了电热、相变制热、化学制热等方法。在空调服未来的发展方向上,伴随可穿戴技术的发展,提出了可穿戴技术与空调服结合应用的新构想,对同时具有生命体征监测和体温调节功能的新型空调服进行了展望。     

Modelling the cooling phase of heat sterilization processes, using heat transfer coefficients

A mathematical model based on finite differences was presented, which improved the accuracy of current modelling techniques during the cooling period for conduction heating foods undergoing thermal processing. The surface heat transfer coefficient between can and cooling fluid was incorporated into the finite difference equations, with a value of 600 W m⁻² K⁻¹ chosen from literature and confirmed by calculations from surface temperature measurements and a correlation of the form Nu = f(GrxPr)ⁿ.
Experimental results were obtained for a cylinder of Sylgard 184 elastomer (length 62mm, diameter 57mm) and a polypropylene block (26x91x141 mm). At the end of cooling the heat transfer coefficient model predicted a centre temperature just 2.5°C above the measured value for polypropylene, and for Sylgard 184 this difference was 2.7°C.
This model will improve both real-time process control via the 'derived-value' technique, and the use of controlled pressure cooling with less damage to containers. Optimization of quality factors will also be improved with increased knowledge of in-container temperatures.     

加热和冷却速率对大豆蛋白凝胶特性的影响

凝胶性是植物蛋白最重要的性质。采用小变形振荡(动态)流变测试研究大豆分离蛋白凝胶网络结构形成。结果表明:在加热阶段,储能模量(G')和耗能模量(G″)都低于1 Pa,G'G″且基本保持恒定直到达到凝胶点。Tanδ值随着加热的进行逐渐降低,然后急剧下降,冷却阶段时降至最低且保持恒定,说明形成强而稳定的凝胶网络结构。当加热和冷却速率增大时(从0.5~4℃/min)G'值逐渐下降,表明最终形成凝胶强度下降;慢的加热(冷却)速率时(0.5、1、2℃/min)tanδ较小,说明相对于快的加热速率(4℃/min)形成了更好三维网络结构的凝胶;凝胶点和加热速率有关而不受冷却速率的影响。随着蛋白质浓度的增大,其凝胶G'值增大、tanδ值减少、凝胶点下降。因此,控制加热和冷却速率可以最大限度的提高热诱导大豆蛋白的凝胶强度,而不用改变蛋白质的浓度。     

Simulation model for moving food packages in microwave heating processes using conformal FDTD method

A numeric model was developed to couple electromagnetic (EM) and thermal field calculations in packaged foods moving in pressurized 915 MHz microwave (MW) cavities with circulating water at above 120 °C. This model employed a commercial EM package with a customized heat transfer sub-model to solve EM field and thermal field equations. Both methods applied finite-difference time-domain (FDTD) method. An interface was built to facilitate the communication between electromagnetic and thermal models to incorporate the coupling feature which is unique to microwave heating process. Special numerical strategies were implemented to simulate the movement of food packages. The simulation model was validated with a pilot-scale microwave system using direct temperature measurement data and indirect color patterns in whey protein gels via formation of the thermally induced chemical marker M-2. Good agreements were observed. Four cases were studied to investigate the influence of power input and package gaps on heating uniformity. These applications demonstrated the flexibility of the model to allow its usage for system and process optimization.     

A critical analysis of mathematical procedures for the evaluation and design of in‐container thermal processes for foods

Kinetic data on thermal destruction of spoilage and quality factors coupled with the temperature history of a product during a heat sterilization cycle are the basic information needed for the evaluation and the design of thermal processes through a physical‐mathematical approach. A critical review on the available physical‐mathematical procedures used for thermal process calculations of in‐container processed foods is presented. The origin and the limitations of each method are discussed. The equations associated with each method, for internal product temperature predictions, are explicitly given. The relative performance of selected methods under identical processing conditions is illustrated. Several problems associated with thermal process calculations are discussed.     

蒸汽加热系统节能及余热利用

节能降耗是造纸企业相当重要的一项工作。沈阳飞鸿达节能技术中心发明了能有效回收提高蒸汽和水利用率的一系列新型节能设备。文章简要介绍蒸汽喷射式设备在造纸行业和其它行业节能工程中的应用。     

Microwave heating of different vegetable oils: Relation between chemical and thermal parameters

Changes of DSC profiles and thermal properties (upon cooling and heating) were evaluated at different times of microwave heating on refined peanut (Pto), high oleic sunflower (HOSo) and canola (Co) oils and compared to the results obtained for standard chemical indices (free fatty acids, peroxide, p-anisidine, OSI time) and antioxidant capacity (Trolox equivalent antioxidant capacity). Co was more extensively oxidised by microwave heating than the other two oils probably as a consequence of the higher degree of unsaturation, even though it showed a higher antioxidant capacity. Microwave heating also induced alterations in both cooling and heating profiles of the oils, mainly in Pto and Co, shifting phase transitions towards lower temperature and enlarging temperature range. High statistical correlation coefficients were obtained among thermal properties both upon cooling and heating and chemical indices (i.e. free fatty acids and p-anisidine values). The analysis of both cooling and heating profiles and related thermal properties appears to be a valuable tool to assess different degrees of lipid thermoxidation induced by microwave in vegetable oils being also very useful for the ready-to-eat food sector and the vegetable oil industry.     

Evaluation of innovative immersion vacuum cooling with different pressure reduction rates and agitation for cooked sausages stuffed in natural or artificial casing

Effects of different pressure reduction rates and liquid agitation (523 rpm) on sausage successful rate, cooling time, cooling loss, texture properties, chemical and physical parameters were analysed by ANCOVA. Tested linear pressure drop rate from 320 mbar to 50 mbar was 20 (L 20), 30 (L 30), or 40 (L 40) mbar/min for artificial casing sausages (ACS) and 60 (L 60), 80 (L 80), or 100 (L 100) mbar/min for natural casing sausages (NCS). From 50 mbar until 6.4 mbar, 5 mbar/min was used for both casings. NCS were more suitable than ACS for IVC. The recommended pressure reduction rate was 30 mbar/min for ACS and 60 mbar/min for NCS. ACS under 30 mbar/min with agitation (LA 30) presented significantly higher texture property values than that without agitation (L 30) (P < 0.05). Cooling time (to 4 °C) of NCS under 60 mbar/min and agitation (LA 60) was significantly shorter than that without agitation (L 60) (P < 0.05). This study could assist meat processors or manufactures when choosing a suitable pressure drop rate for different types of sausages.     

Application of PLSR in correlating physical and chemical properties of pork ham with different cooling methods

Partial least squares regression (PLSR) was applied to understand the relationship between physical and chemical properties of pork leg ham with different cooling treatments, i.e., cold room, air blast and vacuum cooling. The results indicated that overall 69.8% variation of physical matrix was explained by chemical matrix. For the univariate analysis of physical attributes, the results showed that gumminess (88.1%) and hardness (86.5%) were best explained by chemical matrix, followed by springiness (78.7%), Warner–Bratzler Shear force (61.3%), and a* (60.0%). Graphical display of the regression coefficients indicated that different cooling treatments had different effects on the physical property of pork ham. Therefore, to predict the physical quality with chemical attributes, separate regression formulations should be adopted for different cooling methods. These findings have practical importance in attempts to predict physical properties from chemical components. In addition, they can also be used to control the physical properties by adjusting the components in the meat system.     

高压脉冲电场与热灭菌技术相结合对大肠杆菌的杀菌效果

高压脉冲电场灭菌技术是近年来发展起来的极有潜力的非热灭菌技术,但由于其参数较多,对于最佳的灭菌参数至今未有定论。所以该论文提出了一种将高压脉冲电场灭菌与传统的热杀菌技术相结合的灭菌技术,旨在发挥两者的优点,实现一种简单、节能、快速、安全、高效的灭菌技术。通过实验,可以发现,将大肠杆菌在45℃条件下进行预热5min后再进行高压脉冲电场灭菌,大肠杆菌的存活率已降至13.69%。这样既节省了能源,又适用于一些不能够加热至45℃以上的食物灭菌,是一种可以广泛应用的灭菌技术。      

Performance of multi-packaging for table grapes based on airflow,cooling rates and fruit quality

The performance of three table grapes multi-scale designs, namely the 4.5 kg box, 5 kg open-top punnet and 5 kg clamshell punnet, was studied. Results showed that vent-hole ratio of empty grape boxes had a significant influence on the resistance to airflow, where the 5 kg punnet box with a vent-hole ratio of 6.13 ± 0.04% had a lower pressure drop than the 4.5 kg boxes with a lower vent-hole ratio of 3.80 ± 1.74%. The addition of liner films and inner packages changed the pressure patterns, indicating that inner packaging had a great influence on airflow resistance and airflow patterns through multi-scale packages of grapes. Cooling rates of grapes in the 4.5 kg multi-packaging was significantly (P < 0.05) slower than that of grapes in 5 kg punnet multi-packaging, where the 4.5 kg box resulted in a seven-eighths cooling time of 30.30–46.14% and 12.69–25.00% more than that of open-top and clamshell punnet multi-packages, respectively. After 35 days in cold storage at −0.5 °C, grape bunches in the 5 kg punnet box combination (open-top and clamshell) had a weight loss of 2.01–3.12%, while the bunches in the 4.5 kg box combination had only 1.08% weight loss. The bunch stem dehydration rates were also higher in the 5 kg punnet multi-package. These results were attributed to differences in vapour pressure deficit (VPD) measured between the three multi-scale packages, where the VPD inside the 4.5 kg multi-packaging was 40.95 Pa, while the VPD inside the 5 kg open-top and clamshell punnet packaging were 92.97 Pa and 100.71 Pa, respectively.     

Disinfection of fishmeal with radiofrequency heating for improved quality and energy efficiency

Radiofrequency (RF) heating was investigated as an alternative to cooking, drying or chemical disinfection for the preservation of fishmeal and shown to be a highly effective process without any detectable effects, particularly on proteins, lipids or in vivo digestibility. The uniform and deep penetration of RF waves resulted in rapid and homogeneous heating allowing ∼4 times lower thermal loads to be used for >5 log₁₀ (>99.999%) reduction in infection levels for Salmonella spp and for Escherichia coli O157:H7. Simultaneously, the natural flora was reduced by >3 log₁₀ (>99.9%). The RF process can be operated in the 70–90 °C range and with high energy‐use efficiency (∼50%), which compares well with the 10–15% efficiency for conventional surface heating methods. Industry and expert laboratories confirmed these results. RF heating is thus a new alternative thermal process that is particularly appropriate for disinfecting fishmeal or for reprocessing it rapidly and efficiently with full retention of its natural attributes. Copyright © 2005 Society of Chemical Industry     

Efficient and robust multi-objective optimization of food processing: A novel approach with application to thermal sterilization

The optimization of thermal processing of foods is a topic which has received great attention during the last decades. The majority of the authors have considered the use of single-objective (criteria) for the optimization. However, the simultaneous optimization of several objectives is much more realistic and desirable, but the associated non-linear programming problems can be very challenging to solve. Here, we describe an efficient and robust multi-criteria optimization method which can be successfully applied to large dynamic systems, like those arising from the modelling of thermal processing of foods. Further, their capabilities for better design and operation of these processes will be highlighted with selected case studies, where the generated Pareto solutions will be analysed. Finally, we will also illustrate their advantages over other recently proposed strategies.     

Recent developments in applications of radio frequency heating for improving safety and quality of food grains and their products: A review

Abstract

Food grains constitute a vital part of the daily diet of the population worldwide, and are generally considered as safe products with high storage stability due to their low moisture contents. However, post-harvest losses (PHL) caused by insects, fungi, food-borne pathogens, and undesirable enzymes remain a major concern for the grain industry. Thermal treatments are commonly used to reduce the PHL of grains and their products without any chemical residues. Among which, radio frequency (RF) technology has been regarded as a promising alternative to traditional heating methods for improving safety and quality of food grains due to its fast, volumetric, and deep penetration heating characteristics. This review provided comprehensive information about principles of RF technology and its main applications including disinfestation, pasteurization, enzyme inactivation, drying, and roasting for processing food grains and their products. The methods to improve the RF heating uniformity and effects of RF heating on product quality were also reviewed. Finally, the current problems and recommendations for future work related to RF processing of grains and their products were discussed. This review would improve the understanding of RF heating for food grains and their products and promote the application of RF technology in the food grain industry.     

Onion cells after high pressure and thermal processing: comparison of membrane integrity changes using different analytical methods and impact on tissue texture

Two different analytical methods were evaluated for their capacity to provide quantitative information on onion cell membrane permeability and integrity after high pressure and thermal processing and to study the impact of these processing treatments on cell compartmentalization and texture quality. To determine changes in cell membrane permeability and/or integrity the methodologies utilized were: (1) measurement of a biochemical product, pyruvate, formed as a result of membrane permeabilization followed by enzymatic activity and (2) leakage of electrolytes into solution. These results were compared to previously determined methods that quantified cell viability and 1H-NMR T(2) of onions. These methods allowed for the monitoring of changes in the plasma and tonoplast membranes after high pressure or thermal processing. High pressure treatments consisted of 5 min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30 min water bath exposure to 40, 50, 60, 70, or 90 °C. There was strong agreement between the methods in the determination of the ranges of high pressure and temperature that induce changes in the integrity of the plasma and tonoplast membranes. Membrane rupture could clearly be identified at 300 MPa and above in high pressure treatments and at 60 °C and above in the thermal treatments. Membrane destabilization effects could already be visualized following the 200 MPa and 50 °C treatments. The texture of onions was influenced by the state of the membranes and was abruptly modified once membrane integrity was lost. PRACTICAL APPLICATION: In this study, we used chemical, biochemical, and histological techniques to obtain information on cell membrane permeability and onion tissue integrity after high pressure and thermal processing. Because there was strong agreement between the various methods used, it is possible to implement something relatively simple, such as ion leakage, into routine quality assurance measurements to determine the severity of preservation methods and the shelf life of processed vegetables.