Attempts are made in this paper to study the effects of CMC and processing techniques of acidified milk drinks on its stability and particle size distribution, to detect the stability of acidified milk drinks by the centrifugal sedimentation method, and to test the main processing techniques affecting stabilizing effects. Meanwhile the effects of these processing techniques on the particle size distribution of product are determined, and the relationship between the particle size distribution of system and the stability of product is analyzed. The results show that such factors as the addition amount of CMC, pH value, homogenization pressure, acid adjustment temperature will all affect the stability and particle size distribution of acidified milk drinks, of which the addition amount of CMC and homogenization pressure have significant effects on the results, followed by the acid adjustment temperature, and the pH value has the minimum effect on the results.
Acidified milk drinks are made from milk or reconstituted milk as the raw material, with lactic acid fermentation for dilution and acid adjustment, or without fermentation by direct use of organic acids to adjust the pH value to 3.8-4.0. For its rich nutrition, pleasant color and aromatic flavor, it is favored by the vast number of consumers and develops fast in our country in recent years. Since the pH value of acidified milk drink is below the isoelectric point of casein in milk, resulting in weakening of electrostatic repulsion between casein micelles, thus there is a tendency for casein to form larger particles and then precipitate. In production, the product quality is difficult to control, and it is easy to appear flocculent, stratification, precipitation and other phenomena, as well as short shelf life, seriously affecting the development of acidified milk drinks. Therefore, the key to production of acidified milk drink lies in maintaining the stability of dispersion state of casein micelles in milk, and this is often achieved by adding a stabilizer.
CMC is an anionic linear polymer, and at the pH value of acidified milk drinks can produce electrostatic interactions with the positive charges of casein to form a hydrophilic compound. The polymerization between the particles can be avoided so that the particles of casein micelles can be stably dispersed. And it has rich source and cheap price, so in China CMC is mostly used as the stabilizer in acidified milk drinks.
The roles of CMC in acidified milk drinks are as follows.
- . Adding CMC in the acidified milk drinks can make the system form the compound of CMC-casein particles and avoid the polymerization between the particles so that casein micelle particles can be stably dispersed and the stability of product can be improved.
(2). The stability and particle size distribution of acidified milk drinks are affected by such factors as the addition amount of CMC, pH value, homogenization pressure, acid adjustment temperature, of which the addition amount of CMC and homogenization pressure have significant effects on the results, followed by the acid adjustment temperature, and the pH value has the minimum effect on the results. For the product with high stability, the particle size of system is relatively small.