【作者】 邓力；

【导师】 金征宇；

【作者基本信息】 江南大学 ， 粮食、油脂与植物蛋白工程， 2006， 博士

【摘要】 对杀菌技术的领域性分析发现,低酸性、高水分活度、长架寿固体食品的杀菌缺少一种杀菌品质明显优于传统杀菌釜杀菌技术的先进杀菌技术。这种情况造成了固体食品的热敏性成分利用率低和杀菌加工范围限制,还成为中国传统食品工业化的技术瓶颈。流态化固体食品超高温杀菌技术可能解决这一问题,该技术具有全新的技术原理:在无蒸发条件下流态化加热食品颗粒,达到杀菌条件后,再通过减压蒸发冷却或流态化冷却,实现超高温杀菌过程,并通过小量食品的快速杀菌来实现工业生产所需要的效率,是目前唯一一种最终产品是纯粹固体的主食固体食品超高温杀菌技术原理。通过对流态化固体食品超高温杀菌的流体力学、传热学、品质变化动力学、微生物致死动力学和传质学分析,得到相关传递过程和杀菌核心参数基本控制方程,确定和推导出适用的理论基础和计算公式。在完成气固和液固流态化操作条件及表面换热计算后,通过Matlab6.5和ANSYS8.0软件编程以解析或数值方法求得颗粒内部温度分布和可溶性成分浓度分布,在此基础上进行品质变化动力学、微生物致死动力学和传质学分析计算,获得流态化固体食品超高温杀菌的主要技术特征、特性参数和应用范围。发现流态化固体食品超高温杀菌技术具有较宽的流态化操作范围,气固流态化的主要流型为聚式,而液固流态化的流型为散式,同时液固流态化的形成受到两相密度差的限制;流态化对流加热具有流体颗粒表面换热系数高并且所有颗粒换热均匀一致的优势,其内部热传导受表面换热系数和颗粒直径影响很大,直接影响到杀菌品质,直径越大,杀菌品质越差。采用减压蒸发,直径0.25-1.50cm颗粒在7.74-137.6sec/145℃即可达到目标F值;通过不同表面换热系数对杀菌时间影响关系的数值模拟和非线性数据拟合发现,无因次杀菌时间和Bi数存在双曲函数关系,可以用于参数估计,并揭示了颗粒食品对流加热杀菌的内在规律。对液固流态化过程中的传质估算表明,食品中的可溶性成分的传质损失在可接受的范围内。构想并设计制造了流态化固体食品超高温杀菌原理验证设备,该设备具有液固流态化超高温杀菌、常压及真空减压冷却、流态化冷却等功能。通过Visual Basic6.0编程实现核心杀菌操作的自动控制以及压力/温度/F值/C值的采集计算和实时显示。对首次出现的F值/C值的实时采集计算精度问题进行了解析和数值分析,结果表明,温度测量误差对采集精度产生了决定性的影响,并得到保证采集精度的最大步长。在原理验证设备上采用静态热电偶法采集以油脂为流动相的液固流态化超高温杀菌过程中马铃薯试样颗粒中心温度,通过LDSD法计算出表面换热系数hfp值。测算数值与预测值接近,说明本文有关预测计算方法是合理的。通过建立流态化固体食品超高温杀菌的优化数学模型,由Matlab软件编程计算,得到典型条件下最优杀菌技术参数以及相应杀菌效果。与现有固体食品热杀菌技术,重点与连续式液体颗粒无菌工艺进行比较,流态化固体食品超高温杀菌技术具表面换热系数高、杀菌参数推算和热处理效果评价数学模型较简单、工艺灵活等优点,尤其是彻底解决了颗粒停留时间分布(RTD)问题。更多还原

【Abstract】 With investigating on general scope of sterilization technologies, it was found that there was not any sterilization technology that has obvious advantages of products quality over traditional retort sterilization technology being applied to solid food with low acid, high water activity and long shelf life. This situation resulted in both the low utilization ratio of themolabile components of foods and the limit of foods species that can be applied to sterilization, and was a choke point for industrialization of domestic traditional diets. This problem is possible to be dissolved via the fluidization solid foods ultra high temperature (UHT) sterilization, which has a novel technological principle, that is, in non-evaporation condition food particles are heated in fluidization bed to attain commercial aseptic demand, then are cooled by decompressing evaporation cooling or fluidization cooling, so is accomplished the UHT sterilization course. This technology achieves the efficient to meet the demand of industrial scale by rapid sterilization for a small quantity of particulate foods. The fluidization solid foods UHT sterilization is the unique sterilization method in which the final products are pure solid foods with low acid, high water activity and long shelf life.The process of fluidization solid foods UHT sterilization technology were respectively analyzed in hydrodynamics, heat transfer, food quality kinetics, microorganism lethal kinetics, and mass transfer, the basic controlling equations for transfer process and the key parameters of sterilization were established, therefore the appropriate theoretical basis and computational formula were selected or derived. Based on the results of the computation of the operating condition of fluidization and surface heat exchange, the inner distribution of temperature and dissoluble component concentration of particles were acquired via analytical and numerical computation with code programmed by Matlab6.5 and/or ANSYS8.0, then, the analysis of food quality kinetics, microorganism lethal kinetics and mass transfer were done, finally, the primary technology characteristics, key parameters and application field of this technology were obtained. The results revealed that there is wide fluidization operating rate range in fluidization solid foods UHT sterilization, the flow regime of liquid-solid fluidization is particulate fluidization and the flow regime of gas-solid fluidization is mostly aggregative fluidization, and liquid-solid fluidization are limited by density different between two phases; Fluidization convectional heat has the advantages of high surface heat exchange coefficient and uniform surface heat transfer to all particles, the heat conduction inside particle is obviously affected by hfp and diameter of particle, hence so is the quality retention of foods sterilized, the more the diameter and the lower the quality retention. The dimensionless correlation between dimensionless sterilization time and Bi number was expressed as hyperbolic function via numeric simulation and nonlinear data fitting for the effect of hfp on the sterilization time, the correlation displayed radical principle of convectional heat sterilization for particulate foods and could be used to estimate processing parameter. The approximate computation for mass transfer showed that loss of soluble component was acceptable in the fluidization solid foods UHT sterilization.The fluidization solid foods UHT sterilization pilot equipment for the principle validation was conceived, designed and finally manufactured, which have the function of liquid-solid fluidization UHT sterilization, atmospheric pressure/vacuum decompressed evaporation cooling, fluidization更多还原