西红柿汁的多级冷冻浓缩研究

在果汁的悬浮式冷冻浓缩过程中,对于低浓度的果汁为避免冰晶夹带过多,减少能耗和原材料的损失,通常采用多级浓缩的方式得到高浓度果汁。本文以西红柿汁为原料,先后进行了四级的冷冻浓缩,将西红柿原汁从4.2°Bx浓缩5.8倍到24.4°Bx,对试验数据回归模型参数,采用龙格一库塔法进行数值积分求得模型解,建立了西红柿汁的四级冰晶生长动力学模型。模型建立后再对四级浓缩的生长曲线进行综合比较。试验结果表明:在每级的浓缩过程中都经历了缓慢浓缩,加速浓缩,缓慢浓缩三个阶段,同时随着冷冻浓缩的级数增加,浓缩速度逐级放缓,浓缩时间逐级延长,特别是在较高级别的浓缩的中后期,出现了试验数据部分低于拟合数据的现象,该阶段可以认为是冷冻浓缩过程中的一个"关键控制点",这点为指导工业生产中的冷冻浓缩提供一定的理论依据和实践参考。

Multi-level Freeze Concentration of Tomato Juice

In the freeze concentration progress of juice,multi-level concentration was used in the low concentration juices to decrease the ice crystals,the juice loss and the energy consumption.In the experiment,the tomato juice was concentrated from original 4.2° Bx to 24.4° Bx by the four-stage freeze concentration.To establish the dynamic model for the four-stage ice crystal growth,Powell method was adopted and its solution was obtained with numerical integration by using Runge-Kutta method.After that,the concentration curves of the four stages were compared comprehensively.The results showed that every stages of the freeze concentration go through three processes of slow concentration,accelerating concentration and slow concentration.The concentration time becomes longer when the concentration speed slows down stage by stage.Especially,in the middle and late stages of the concentration,the experiment data are lower than the fitting data.This stage is the critical control point of the freeze concentration.This result provides a theoretica1 basis and a practical reference for the industrial production.