上海交通大学

硕士学位论文

羧甲基纤维素钠溶液的流变性质及其对酸性乳体系的稳定作用

姓名：李静

申请学位级别：硕士

专业：材料学

指导教师：张洪斌

20070101

羧甲基纤维素钠溶液的流变性质及其对酸性乳体系的稳定作用

摘 要

羧甲基纤维素钠（CMC）溶液的流变性质使其在许多领域中得到应用，研究CMC溶液的流变性质将有利于开发新的应用以及对已有的应用进行改进。CMC可用于酸性乳体系中作为稳定剂，对其在酸性条件下与酪蛋白胶粒的作用进行研究，将对实际应用具有一定的指导意义。

CMC水溶液一般呈假塑性，其零剪切粘度随CMC分子量、取代度（DS）的升高而增加，但取代度对溶液流变性质的影响较小。溶液的粘度亦随浓度增加而上升，当CMC浓度足够高时体系形成凝胶。随pH值降低，溶液的粘度下降，但低于CMC的pKa值时，粘度又略有升高。CMC溶液具有典型的聚电解质效应。当CMC溶液中加入一价阳离子Na+、K+后，粘度随加入的盐离子浓度的升高而降低。而二价阳离子Ca2+的加入，使溶液的粘度先下降后升高，溶液中有CMC超结构存在。当DS增加时，Ca2+的加入会导致CMC发生沉淀。Mg2+与Ca2+有相似作用，使溶液的粘度先下降后略有升高，但影响较小。加入蔗糖则使溶液粘度升高。

CMC可用于酸性乳体系中起稳定作用。在酪蛋白等电点（pI=4.6）

以下，CMC通过静电作用吸附于酪蛋白表面，由于静电排斥和空间位阻作用使体系稳定，同时CMC对体系还具有增稠作用。分子量大、取代度高的CMC稳定效果好，其中分子量对稳定性的影响较大。当CMC浓度低时（c < 0.3%），CMC与酪蛋白胶粒发生架桥絮凝而加速体系的失稳，随CMC浓度升高，体系趋于稳定。pH值对体系的稳定性也有影响。加入蔗糖可以提高体系的粘度，使稳定性增加。酸性乳制备的工艺参数亦对稳定性产生影响。均质可使体系稳定，但是过高的均质压力会使CMC发生降解。混合温度对稳定性影响不大。在低温下调酸可提高体系的稳定性。调酸时增加搅拌速率使CMC与酪蛋白充分接触可使体系更为稳定。

关键词：羧甲基纤维素钠（CMC），流变学，酸性乳体系，酪蛋白，稳定性

RHEOLOGICAL PROPER4TIES OF CMC AQUEOUS

SOLUTIONS AND ITS APPLICATION IN THE

STABILIZATION ON ACIDIFIED MILK DRINKS

ABSTRACT

Carboxymethylcellulose, CMC, in aqueous solutions are used in manyapplications that exploit its rheological properties. If new applications are tobe found and existing ones improved, it is necessary to determine theviscoelastic and rheological material functions of the solution system so thatthey can be employed during processing and in the subsequent use of aproduct. CMC can be used in acidified milk drinks as stabilizer. It will beuseful for this application to study the interaction between CMC and caseinmicelles at low pH.

CMC aqueous solution exhibits pseudoplastic behaviour. Zero-shearviscosity increases with the molar mass and degree of substitution (DS).While increasing the concentration of CMC, the viscosity increases, and it

can form gel when the concentration is high enough. The viscosity of CMCsolution decreases with the pH. When lower than pKa, the viscosity risesagain. The CMC solutions have polyelectrolyte effect. By adding monovalent(Na+, K+), this polyelectrolyte effect can be increasingly compensated for.Bivalent low-molar-mass electrolytes (Mg2+, Ca2+) also hinder the volumeexpension of a polyelectrolyte coil. An increase in the salt concentration firstcauses a fall in the viscosity. If the salt concentration is further increased, theviscosity rises again. A explanation offered for the viscosity increase is theformation of superstructures via bridging bivalent ions. In highconcentrations, large bivalent cation (Ca2+) leads to flocculation for CMCwith higher DS. By adding sucrose, the viscosity of CMC solution increases.

CMC can be used in acidified milk drinks as stabilizer. The adsorptionof CMC onto casein micelles is driven by electrostatic force and takes placeat and below pI. The casein micelles can be stabilized by electrostaticrepulsion and steric repulsion provided by CMC layer. CMC also works as athickener. CMC with higher molar mass, DS or concentration is of muchmore benefit to the stabilization on AMD while the addition of extreme lowconcentration of CMC make the AMD unstable due to the aggregation ofcaseins through bridging. pH also has effect on the stabilization. The additionof sucrose can increase the viscosity of the system, which is useful.

Homogenization is needed to improve the stability, but CMC degrades athigh pressure. The mixing temperature has no significant effect on thestability. Acidifying at lower temperature and higher stir rates are beneficial.KEY WORDS：carboxymetylcellulose (CMC), rheology, acidified milkdrinks (AMD), casein micelle, stability

符号说明

CMC 羧甲基纤维素钠

η 粘度

η0 零剪切粘度

M

DS

c

η*

G'

G''

ω

AMD

V0

D

ρS

ρ 分子量 取代度 浓度 复粘度 储能模量 损耗模量 角频率 酸性乳饮料沉降速率颗粒粒径 流体密度颗粒密度

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