【作者】 高明才；

【导师】 陈锦权；

【作者基本信息】 福建农林大学 ， 农产品加工及贮藏工程， 2009， 硕士

【摘要】 冷冻浓缩作为非热加工技术,可以最大限度的保留食品原有的生鲜风味和营养,其挥发性芳香成分损失和酶、色素等热敏性成分的变化极小,其独特的优势,将成为食品加工技术研究的热点之一,在理论和实践应用中都有着巨大的潜力。但由于冷冻浓缩产生的冰晶夹带率比较高且难以分离,未有合适的冷冻浓缩设备,从而限制了它的推广与使用。为解决冰晶夹带问题,国内外学者大多把目光停留在单位冰晶体积的层面上,主要凭经验或以实测资料为依据来控制冰晶的生长过程。本文利用相场法从微观上分析冰晶生长的机制,探索冰晶组织的形成规律和控制方法,较为系统地展开对冷冻浓缩技术的研究。具体研究工作和主要结论如下:(1)研制出实验室用冷冻浓缩设备。将结晶罐与生长罐合并,避免冰晶向结晶罐转移的过程中再次污染的危险。利用中心排冰法,有效地实现了大小冰晶的分离,降低了果汁的损失率。(3)西瓜汁为实验材料,经过15个小时,浓度从9(brix)浓缩到46.6(brix),西瓜汁在浓缩过程中,前期果汁的损失率远远大于后期的损失率,其第1～7小时冰晶中的可溶性固形物占总损失率的67.7%,第8～10小时西瓜汁损失率的12%,第11～15小时冰晶中的可溶性固形物占总损失率的20.3%。在浓缩前期由于冷媒和浓缩液温差大,冰晶生成量多,后期温差减小,冰晶生成量少。(4)推导出结晶罐总传热系数K=0.195kJ/(m2·s℃),实验室准备建设一条中等规模的冷冻浓缩设备,K可作为设计结晶罐传热面积的依据。(5)冰晶是典型的凝固组织,因其非平衡组织结构涉及到热量、质量和动量传输以及界面动力学和毛细作用效应相藕合的自由边界问题,故引入相场模型。用于模拟冷冻浓缩过程中冰晶生长的微观组织的演变过程。探讨了相场模型建立的基本原理、其数值求解的离散处理、稳定条件、初始条件和边界条件等问题。(6)利用相场模型对纯水的冰晶生长过程进行数值模拟,模拟四个过冷时间、三个过冷度下的冰晶生长的演化过程。更多还原

【Abstract】 Freezing concentration as a non-thermal processing technologies, it is able to maximize the retention of the original fresh flavor of food and nutrition, the minimal changes in the Loss of volatile aromatic components and heat-sensitive components Of enzymes, color ,its unique advantages, will become the study of food processing technology, one of the hot spots. However, due to freeze concentration of ice crystals have a relatively high rate of entrainment, and it is difficult to be separated from the solution .The frozen concentrate that no appropriate equipment,its promotion and use is limited. Since a long time, in order to address the issue of entrainment of ice crystals, the unit size of ice crystals was concerned by domestic and foreign experts and scholars who con- trolled the growth of ice crystals based on the measured datas or main experience.This paper, the development of an appropriate frozen concentrated equipment used in laboratory . Through domestic and international field of metal micro-structure of the phase-field model, the law of formation of ice crystals and methods of controlling were explored. Specific research work and the main con- clusions were as follows:(1)Design a freeze concentration equipmentused in laboratory,crystallizer can be combined with the growth of pot that reduce the contamination,the remove ice methods can effective implementation of the separation of the size of ice crystals.(2)Design a freeze concentration equipmentused in laboratory,crystallization can be combined with the growth of pot that reduce the contamination,the remove ice methods can effective implementation of the separation of the size of ice crystals.(3)Watermelon juice for the experimental material Changes from 9(brix) to 46.6(brix). Watermelon juice in the enrichment process, Pre-loss rate of fruit juice is much larger than the late loss rate .its first 2 ~ 8 hours ,the loss rate of ice crystals in soluble solids reach to 71.8%,from 9～15h the loss rate of ice crystals in soluble solids reach to 27.1%, As a result, in the pre-freezing concentration , large temperature difference, ice crysta amount is large; in the later period ,small temperature differences ice crysta amount is small. (4) Obtain the heat transfer coefficient K=0.195kJ/(m2·s). Laboratory is going to build a set of medium equipment for freezing concentration, the K Can be used as the basis for the design of the crystallizer.(5)Ice crystal was a typical kind of solidfication structure. The phase-field model was introduced because of its non-equilibrium from its typical structure,involving energy,quality and momentum transfer,as well as the interface kinetics and the problem caused by capillarity effects coupled with the free boundary. Taken advantages of phase-field model which could change the sharp interface from the course of interface evolution into the diffuse interface, it was used to simulate the process of evolution of microstructure in the process of ice crystal growing of freeze concentration. The basic principles of phase-field,the discrete numerical solution, stability conditions, initial conditions and boundary conditions were discussed.(6)The growth process of ice crystals of supercooling water was numerically simulated by phase-field model, which including the course of evolution of ice crystal morphology at different cooling time, different degrees of supercooling.更多还原